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Glossary of Terms

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100-Year Event – A flooding event that has a one percent chance of occurring in any given year. The term "100-year" is a measure of the size of the flood, not how often it occurs. Several 100-year floods can occur within the same year or within a few short years. The District uses the 100-year event as the basis for regional facility design. The 100-year event for any given area is based on a statistical frequency analysis of local rainfall data. The analysis determines the amount of rainfall that would only have a one percent chance of occurring in a given year. Hydrologic analysis is then applied to the watershed, based on the 100-year rainfall magnitude. The result provides the expected discharge of the watershed during a 100-year event. The District’s hydrology manual includes isohyetal maps, which indicate the expected magnitude of rainfall within an area based on a specific return frequency.

303(d) Impaired Water Body – is an impaired water body in which water quality does not meet applicable water quality standards and/or is not expected to meet water quality standards, even after the application of technology based pollution controls required by the Clean Water Act. Section 303(d) requires the establishment of TMDL’s for these water bodies. The discharge of urban runoff to these water bodies by the Co-permittees is significant because these discharges can cause or contribute to violations of applicable water quality standards.


Acre-foot – The volume of water needed to cover an acre of land to a depth of one foot; equivalent to 43,560 cubic feet or 325,851 gallons.

Ad Valorem Property Taxation – Any source of revenue derived from applying a property tax rate to the assessed value of property. The District’s enabling act allows it to collect ad valorem taxes for flood control purposes. The funds are collected by District Zone and must be spent in the Zone they were collected.

Assessor’s Maps – Maps produced by the Assessor. These maps, also called Assessor's Plat Maps or AP Maps, depict and identify land units within the Assessor's jurisdiction by Assessor's Parcel Number (APN).

ASTM International – Founded in 1898, ASTM International is a not-for-profit organization that provides for the development and publication of voluntary consensus standards for materials, products, systems, and services. In over 130 varied industry areas, ASTM standards serve as the basis for manufacturing, procurement and regulatory activities. Formerly known as the American Society for Testing and Materials, ASTM International provides standards that are accepted and used in research and development, product testing, quality systems, and commercial transactions around the globe. ASTM standards and testing methods are used by District Engineers to establish quality control for concrete strength, soils compaction and steel strength.

Area Drainage Plan (ADP) – A financing mechanism used to offset taxpayer costs for proposed drainage facilities. The fees are imposed on new development within the plan area. The Subdivision Map Act requires that agencies imposing fees have a general drainage plan for the fee area, a special fund for the fees and an equitable distribution of the fees prior to implementation. Since the District does not have land use authority, it cannot implement drainage fees directly. The District must therefore request that the County and/or local cities adopt drainage fees within their jurisdictions for the District. The District generally agrees to create the special funds for the fees and to prepare an ADP. The ADP is a document specifically prepared for the County and cities to adopt. The Area Drainage Plan is essentially the Master Drainage Plan with additional language supporting the costs and distribution of the fee within the plan area. To ensure the equitable distribution of fees, the ADP/MDP boundaries are generally based on watersheds. The total costs of facilities within the watershed are first calculated. The watershed area is then adjusted to discount publicly owned lands and areas on steep slopes not likely to develop. Finally, the total facility cost is divided by the revised watershed area to determine a per acre fee for the plan area. Due to State Law, the collection of drainage fees varies depending on the type of development. Developments falling under the Subdivision Map Act (those requiring a division of lands) pay fees on a per acre basis. Developments falling outside of the Subdivision Map Act (known as discretionary developments) can only be assessed fees based on their impacts to the watershed. The ADP Rules and Regulations state that these impacts can be related to the amount of impervious surface area that the development creates. Therefore, discretionary developments are charged not on a gross acreage basis, but on the total impervious acreage created by their development.


Acre-foot – The volume of water needed to cover an acre of land to a depth of one foot; equivalent to 43,560 cubic feet or 325,851 gallons.

Ad Valorem Property Taxation – Any source of revenue derived from applying a property tax rate to the assessed value of property. The District’s enabling act allows it to collect ad valorem taxes for flood control purposes. The funds are collected by District Zone and must be spent in the Zone they were collected.

Assessor’s Maps – Maps produced by the Assessor. These maps, also called Assessor's Plat Maps or AP Maps, depict and identify land units within the Assessor's jurisdiction by Assessor's Parcel Number (APN).

ASTM International – Founded in 1898, ASTM International is a not-for-profit organization that provides for the development and publication of voluntary consensus standards for materials, products, systems, and services. In over 130 varied industry areas, ASTM standards serve as the basis for manufacturing, procurement and regulatory activities. Formerly known as the American Society for Testing and Materials, ASTM International provides standards that are accepted and used in research and development, product testing, quality systems, and commercial transactions around the globe. ASTM standards and testing methods are used by District Engineers to establish quality control for concrete strength, soils compaction and steel strength.

Area Drainage Plan (ADP) – A financing mechanism used to offset taxpayer costs for proposed drainage facilities. The fees are imposed on new development within the plan area. The Subdivision Map Act requires that agencies imposing fees have a general drainage plan for the fee area, a special fund for the fees and an equitable distribution of the fees prior to implementation. Since the District does not have land use authority, it cannot implement drainage fees directly. The District must therefore request that the County and/or local cities adopt drainage fees within their jurisdictions for the District. The District generally agrees to create the special funds for the fees and to prepare an ADP. The ADP is a document specifically prepared for the County and cities to adopt. The Area Drainage Plan is essentially the Master Drainage Plan with additional language supporting the costs and distribution of the fee within the plan area. To ensure the equitable distribution of fees, the ADP/MDP boundaries are generally based on watersheds. The total costs of facilities within the watershed are first calculated. The watershed area is then adjusted to discount publicly owned lands and areas on steep slopes not likely to develop. Finally, the total facility cost is divided by the revised watershed area to determine a per acre fee for the plan area. Due to State Law, the collection of drainage fees varies depending on the type of development. Developments falling under the Subdivision Map Act (those requiring a division of lands) pay fees on a per acre basis. Developments falling outside of the Subdivision Map Act (known as discretionary developments) can only be assessed fees based on their impacts to the watershed. The ADP Rules and Regulations state that these impacts can be related to the amount of impervious surface area that the development creates. Therefore, discretionary developments are charged not on a gross acreage basis, but on the total impervious acreage created by their development.


Basin – A basin functions the same way as a dam, but usually does not require an embankment to impound water. Basins are dug into the ground and store water at or below grade. Basins have outlet pipes that release flows at a predefined rate. Any flows that enter the basin at a rate in excess of the outlet pipe’s capacity are temporarily stored in the basin.

Best Available Technology (BAT) – BAT is the acronym for best available technology economically achievable. BAT is the technology-based standard established by congress in the CWA for industrial dischargers of storm water. Technology-based standards establish the level of pollutant reductions that dischargers must achieve, typically by treatment or by a combination of treatment and best management practices, or BMPs. For example, secondary treatment (or the removal of 85% suspended solids and BOD) is the BAT for suspended solid and BOD removal from a sewage treatment plant. BAT generally emphasizes treatment methods first and pollution prevention and source control BMPs secondarily. The best economically achievable technology that will result in reasonable further progress toward the national goal of eliminating the discharge of all pollutants is determined in accordance with regulations issued by the Environmental Protection Agency Administrator. Factors relating to the assessment of best available technology shall take into account the age of equipment and facilities involved, the process employed, the engineering aspects of the application of various types of control techniques, process changes, the cost of achieving such effluent reduction, non-water quality environmental impact (including energy requirements), and such other factors as the permitting authority deems appropriate.

Beneficial Uses – are defined as the uses of water necessary for the survival or well being of man, plants, and wildlife. These uses of water serve to promote the tangible and intangible economic, social, and environmental goals. “Beneficial Uses” of the waters of the State that may be protected against include, but are not limited to, domestic, municipal, agricultural and industrial supply; power generation; recreation; aesthetic enjoyment; navigation; and preservation and enhancement of fish, wildlife, and other aquatic resources or preserves. Existing beneficial uses are uses that were attained in the surface or ground water on or after November 28, 1975; and potential beneficial uses are uses that would probably develop in future years through the implementation of various control measures. “Beneficial Uses” are equivalent to “Designated Uses” under federal law.

Bid Estimate – An estimate of the total cost of the construction project. There are generally two types of bid estimates. The first is the “engineer’s estimate”, which is the estimate prepared by the District Engineer during the design process for budgeting purposes. The other is the “Contractor’s Estimate”, which is received during the bidding process. The contractor’s estimate is the estimate of the contractor’s costs (including profit) to complete the project. Generally, the District will publicly announce the proposed project and a date by which all bidders must return a sealed proposal including the contractor’s bid estimate. On that date, the District will open all the sealed proposals and announce the contractor with the lowest estimate. If that contractor meets all minimum qualifications to perform the work, they will be awarded the contract.

Bid Items – A list of “Items of Work” that have been identified, the complete list of which would define all work necessary to complete the construction contract. These items are usually listed towards the front of the contract document. The list, referred to as a proposal, includes the Bid Item, the unit of measurement (Lump Sum, Cubic Yards, Lineal Feet, Each, etc), and the estimated quantity of material necessary to complete that item of work. This identification of bid items and quantities is usually prepared by the District’s Design Engineer. Detailed descriptions of the bid item requirements are included in the Special Provisions and Detailed Specifications portion of the Specifications and Contract Document.

Blue Line Stream – Any stream shown as a solid or broken blue line on 7.5 Minute Series quadrangle maps prepared by the U.S. Department of the Interior Geological Survey (USGS). A blue line stream may be any creek, stream or other flowing water feature, perennial or ephemeral, indicated on USGS quadrangle maps, with the exception of man-made watercourses. The United States Army Corps of Engineers uses USGS blue line stream markings as a preliminary indicator of “Waters of the United States”. Streams identified on USGS maps in such a manner are therefore generally subject to federal environmental regulations.

BMP – Best Management Practices (BMP) are the practice or combination of practices that are determined to be the most effective, practicable means of preventing or reducing the amount of pollution generated by point and non-point sources to a level compatible with water quality goals (including technological, economic, and institutional considerations). BMPs are defined as schedules of activities, prohibitions of practices, maintenance procedures, and other management practices to prevent or reduce the pollution of waters of the United States. Best Management Practices include practices to control runoff during construction (such as silt fences). Other examples of BMPs may include public education and outreach, proper planning of development projects, proper clean out of catch basin inlets, and proper sludge or waste handling and disposal, among others.

Boundary Survey – A survey for the express purpose of locating the corners and boundary lines of a given parcel of land. This involves record and field research, measurements, and computations to establish boundary lines in conformance with the Professional Land Surveyors Act. Easement lines may also be located and/or established with this type of survey.

Budget Hearing – Each year the District holds public hearings for the specific purpose of receiving flood control project requests. These hearings are held in a centrally located public place in each of the District’s seven taxing zones. Any individual or group from the private or public sector may make a request for a flood control project by appearing at the hearing or by submitting a written request to the District prior to the hearing. Support for existing budgeted projects may also be offered. At the public hearing, all requests will be considered by the District's Zone Commissioners and staff and, where appropriate, an open discussion may occur. After the public hearings the District staff prepares cost estimates of all new project requests and ongoing projects and then prioritizes them on the basis of public need, necessity and funds available. A draft budget is then prepared by the District staff and is presented to the Zone Commissioners at a second set of public meetings (work sessions) which are tentatively scheduled for January.

Budget Workshop – The work session that finalizes the tentative budget proposal for that taxing zone. The District presents the draft budget to the Commissioners, who review it in detail with District staff and make adjustments as they deem appropriate before making a recommendation for approval. The work session is a public meeting however, the Commissioners do not take requests or testimony at this session.


California Endangered Species Act (CESA) – The Act was originally adopted in 1970. It requires the California Department of Fish and Game to inventory all threatened fish and wildlife, develop criteria for rare and endangered species and report to the Governor and Legislature every two years on the status of those species. In 1984 the Act was amended to more closely resemble the federal Endangered Species Act. One of the Acts many requirements include that all government agencies undertaking activity that alters the bed, channel or bank of any stream, creek or river obtain a Section 1601 Streambed Alteration Permit from the California Department of Fish and Game. Species protected under CESA are not necessarily protected under the federal ESA and vice versa.

California Environmental Quality Act (CEQA) – First enacted in 1970 to provide long-term environmental protection, the law is the foundation of environmental law and policy in California. CEQA encourages the protection of all aspects of the environment by requiring state and local agencies to prepare multidisciplinary environmental impact studies. Any project that requires the discretionary approval of a state or local legislative body must comply with CEQA requirements. CEQA has six major objectives: 1) to disclose to decision makers and the public the significant environmental effects of proposed activities, 2) to identify ways to avoid and reduce environmental damage, 3) to prevent environmental damage by requiring implementation of feasible alternatives or mitigation measures, 4) to disclose to the public reasons for agency approval of projects with significant environmental effects, 5) to foster interagency coordination in the review of projects and 6) to enhance public participation in the planning process. The act requires projects subject to the regulations to prepare an Initial Study (IS) to determine whether the project could have significant environmental impacts. If no impacts are found, a Negative Declaration (NEG DEC) can be filed. If potentially significant impacts are discovered, an Environmental Impact Report (EIR) is required to analyze the level of impacts and suggest mitigating measures. These documents must be made available to the public for review and comment. At the end of the comment period, the agency may revise the project and environmental documents per any legitimate comments received and may file a Notice of Determination (NOD) stating that the agency is carrying out the project as proposed.

Cast In Place Pipe (CIPP) – A storm drain construction method where the pipe is formed in the pipe trench. The process is accomplished with a slip form and requires soils that are stable at steep slopes. CIPP construction methods are generally less expensive than RCP construction methods. Unfortunately, the proper soil conditions for CIPP construction are rare.

Catch Basin – Curbside opening that collects rainwater from streets and serves as an entry point to the storm drain system.

Change Order – A negotiated amendment to the Original Construction Contract Document that covers a specific change in the design of and/or payment for the project. Change orders are usually required when an unforeseen problem arises in the field. The problem could be a utility line discovered in the field that conflicts with the projects alignment, a mistake on the plan sheets, an unknown soil condition that prevents the expected progression of the work, or a myriad of other things. Change orders usually require the coordination and cooperation of the contractor, the District’s Design Engineer and the District’s Inspection Staff.

Channel – A flood control conveyance system that is partially exposed to the atmosphere. Water in channels flow due to the forces of gravity. Channels include natural waterways, concrete flumes and other similar conveyances. Channels can be lined with a number of materials or combinations of materials. Selection of material type is usually dependent on environmental constraints and channel velocities. Analysis of channels can be done with a number of software packages including WSPGW for prismatic channels and/or HEC-2/HEC-RAS for more complex non-prismatic channel systems. Channels are usually set in the ground such that the design water surface elevation is at least one foot below adjacent ground.

Clean Water Act (CWA) – The Clean Water Act (CWA) contains a number of provisions to restore and maintain the quality of the nation’s water resources. One of these provisions is Section 303(d), which establishes the TMDL program. It also includes provisions regulating point source and nonpoint source pollution.

Concrete – Concrete is a mixture of two components: aggregate and paste. The paste, comprised of Portland cement and water, binds the aggregates (sand, gravel and crushed stone) into a rocklike mass as the paste hardens due to the chemical reaction between the water and the cement. Concrete is usually made up of 60-75% aggregates and 25-40% paste. The quality and strength of concrete is greatly dependent on the paste, which must completely coat each particle of aggregate and fill all the space between the aggregates. Concrete is excellent at resisting compressive forces. Its ability to resist tensile forces (forces that stretch or pull), however, is generally only about 10% of its ability to resist compressive forces. The District uses concrete to construct channels, storm drains, catch basins and a number of other structures required for flood control. Different structures require different qualities of concrete. The District generally specifies 3 classes of concrete, which are differentiated by the amount of cement required and the minimum required compressive strength. Class “A” Concrete is used for retaining walls and other structural concrete facilities. Class “B” concrete is used for nonstructural flood control features like cutoff walls. Class “C” concrete is often called “slurry” and is used to fill voids that can form behind existing concrete linings or be placed in other areas where erosion resistant fill is required. See the chart below for more detail: Typical District Concrete Class Specification and Uses Concrete Class Minimum Cement Requirement Minimum Compressive Strength Use A 6 sacks/CY 4,000 psi Structural Flood Control Components B 5 sacks/CY 3,000 psi Non Structural Flood Control Components C 2 sacks/CY n/a Fill voids, erosion resistant cover.

Concrete Compressive Strength – A measurement used to analyze the quality and strength of concrete. The measurement usually specifies the minimum compressive strength that must be attained by a concrete sample by the 28th day after its placement. It is defined as the measured maximum resistance of a concrete specimen to axial loading, expressed in pounds per square inch. Strength tests are usually performed on test cylinders at the 7-day and 28-day marks. ASTM C192 specifies the collection procedure for samples used to determine compressive strength. The test requires that a sample of the concrete mix be placed in a cylinder 12 inches by 6 inches in diameter. The wet concrete is placed in the cylinder in 3 approximately equal layers, with each layer being rodded (by a small diameter steel rod) 25 times. After the third layer is rodded, the test cylinder is capped and taken to a lab for safe storage. ASTM C617 specifies the necessary preparations to test the cylinders and ASTM C39 specifies the actual test. The test procedure specifies that the cylinder be placed in a machine that applies a compressive force on the test cylinder. The force is gradually increased until the cylinder fails. Dividing the maximum applied force to the cylinder by the cylinder’s cross sectional area provided the maximum compressive strength of the test specimen. This strength is then compared to the minimum concrete compressive strength required by the District’s design engineers.

Concrete Construction Specifications – That section of the District’s Specification and Contract Documents, within the Detailed Specifications Section, that covers the requirements, materials, methods, testing, measurement and payment for concrete construction. The section also specifies how concrete is to be placed and cured, the location and types of joints and weep holes, and any specific requirements for the various types of concrete structures to be placed in the field (reinforced concrete box, channel wall, channel invert, cutoff walls, catch basins, etc.).

Condemnation – The process by which property is acquired for public purposes under the power of eminent domain. Government agencies pursuing condemnation must prove that a public necessity exists that requires the taking of the property.

Conditional Letter of Map Revision (CLOMR) – This letter from FEMA provides comments on a proposed project and its resulting affect on revising a FIRM if the project is constructed. It indicates whether the project meets NFIP criteria. Documentation justifying the proposed projects impact on the floodplain within the District’s jurisdiction must be reviewed and approved by the District’s Floodplain Management Staff prior to being submitted to FEMA for a CLOMR. The Floodplain Management Staff also prepare CLOMR studies for proposed District Project’s within FEMA jurisdiction. The studies consist of a number of elements including a pre-project hydraulic model that is capable of matching the existing FEMA hydraulic model (Duplicate Effective Model) and a post project hydraulic model representing the changes the project will generate.

Confluence – The joining of two flood control facilities.

Critical Depth – Identified as the depth of flow that requires the least energy to perpetuate for a given flow rate. Critical depth is important to design engineers because its occurrence can be predicted. Knowing where critical depth can occur allows a design engineer to establish or verify control points in their hydraulic model. It is also important because critical depth can be difficult to maintain. Slight perturbations in a channel or storm drain section could cause significant changes in flow depth. For this reason, engineers often design channels so that they will be well into the subcritical or supercritical flow regimes.

Construction Survey – Construction staking of improvements shown on improvement plans for control of construction on developments for storm drains, channels, roads, etc.

Contour – An imaginary line on the ground, all points of which are at the same elevation above a specified datum surface. A contour is illustrated by the shoreline of an imaginary body of water whose surface is at the elevation represented by the contour. A contour forming a closed loop around lower ground is termed a depression contour. The District orthophoto and design maps generally use NGVD29 as the datum surface.

Contour Interval – The vertical difference represented between each contour line. For district orphophoto mapping, the contour interval is 4 feet. This means there is a 4-foot elevation change between each line plotted.

Control Survey – Precise location of horizontal and vertical positions of points for use in boundary determination, mapping from aerial photographs, construction staking, and other related purposes.

Court Exhibit Survey – Analysis of various legal descriptions and survey maps; field locating of record, existing monuments, and physical features; and mapping showing this information for the purpose of presenting a visual exhibit to be used in a courtroom.

County Surveyor – On April 9, 1850, the legislature adopted an Act prescribing the duties, and fixing the compensation of County Surveyors. In general, the county surveyor is authorized to practice land surveying and is subject to all provisions of the Professional Land Surveyors Act. The county surveyor is an ex officio deputy recorder for the purpose of copying each map filed for record and is required to make all county, road, district, and other maps and all assessors block books for the county. The County Surveyors office performs most survey functions for the County of Riverside. The District has its own in house survey staff, but is required to file Records with the County Surveyor’s Office.

County Recorder – The recorder's office is responsible for providing constructive notice of private acts and creating and maintaining custody of permanent records for all documents filed and recorded in Riverside County. The office of recorder provides public access to information regarding land and land ownership. The county recorder files records of survey and maintains indexes by the name of grant, tract, subdivision, or United States Public Lands. Copies of the record of survey are available to the public and the original can be produced upon demand.

Cubic foot per second (ft3/s, or cfs) – Rate of water discharge representing a volume of 1 cubic foot passing a given point during 1 second, equivalent to approximately 7.48 gallons per second or 448.8 gallons per minute. In a stream channel, a discharge of 1 cubic foot per second is equal to the discharge at a rectangular cross section, 1 foot wide and 1 foot deep, flowing at an average velocity of 1 foot per second.


D-Load – A design criterion used by engineers to specify the strength of precast reinforced concrete pipe (RCP) for storm drains. The D-Load represents the maximum force that will bear down on the RCP once it has been put in place and backfilled. The load includes the dead load (weight of the fill over it) and the live loads (weight of the largest vehicle expected to pass over the RCP). The D-Load represents the combination of the dead and live loads, with factors of safety, divided by the diameter of the pipe. The manufacturer produces the pipe to meet the specified loading criteria. District Materials Inspection Staff usually require the pipe manufacturer to supply a few sections of pipe for testing purposes to ensure that they meet the minimum loading requirements.

Dam – Dams are usually constructed by making a large embankment that blocks an existing watercourse. This embankment is used to control the release of flood waters downstream of the Dam. Dams usually contain a small outlet pipe that limits the amount of water that can exit the dam. Any flows in excess of the capacity of the dam outlet are stored behind the dam. Most dams are regulated by the Department of Water Resources, Division of Safety of Dams.

Design Mapping – Mapping requested by Design Engineers specifically for the preparation of plans for a specific District project. Depending on the project, the mapping can be provided at horizontal scales of 1”=50’, 1”=40’ or 1”=20’. The contour interval of the mapping is generally 1 foot. The mapping generally includes a number of additional plan metric features not provided on typical orthophoto mapping.

Detailed Specifications – A detailed, exact statement of particulars, prescribing materials and methods, quality and payment for specific items of work for the project. The detailed specifications cover items such as mobilization, water control, traffic control, clearing work, earthwork, trench safety systems, concrete construction, precast reinforced concrete pipe, cast in-place concrete pipe, fences and gates, miscellaneous construction items, dust abatement and NPDES requirements for District Projects. This is where you would find information on strength, testing and placement of materials. See the “concrete construction specifications” for a more detailed example of the information provided in the Detailed Specifications.

Digital Terrain Map (DTM) – a three-dimensional computer model of the terrain of a given area. These maps are created using digital photogrammetric equipment. The raw maps are then supplemented by any additional survey data that has been collected. The photogrammetrist generates the final contour maps from the DTM. DTMs are also provided to the District’s engineering staff for design and planning purposes. District Engineers can use CAD software to manipulate the DTMs for the purposes of generating cross sections or profiles along a project alignment. The DTMs can also be used to estimate earthwork quantities.

Discharge – Another term for stream flow; it is the measured volume of water that moves past a point in the river in a given amount of time. Discharge is usually expressed in cubic feet per second. The average discharge of the Columbia River in September at The Dalles, Oregon, is about 120,000 cfs, which would fill the Seattle Kingdome in less than 10 minutes.

Dry Density – Soils are made of three components – air, water and solids (soil particles). Dry Density is a ratio of the mass of the solids in a compacted soil sample to the total volume of the sample (including the volume taken by air, water and the solids). The dry density of a soil sample is usually obtained by determining the volume of a given sample of soil, baking it to evaporate all the water, then measuring its mass.


Eminent Domain – The right by which a sovereign government, or a person or agency acting under its authority, may acquire private property for public or semi-public use upon payment of reasonable compensation and without consent of the owner.

Easement – A non-possessing interest held by the District in the land of another whereby the District is accorded partial use of such land for a specific purpose. An easement restricts but does not abridge the rights of the fee owner to the use and enjoyment of the land. Easements may be given for surface rights, subsurface rights or overhead rights. For example, the District may use an easement to obtain rights to construct a storm drain through someone’s property. The easement would give the District the right to perform maintenance of the facility and would restrict the property owner from placing structures over the facility. The easement would allow the owner to continue to plant grass or otherwise use the property, while saving the District the costs of having to outright purchase the property.

Endangered Species Act (ESA)– An act passed by Congress in 1973 intended to protect species and subspecies of plants and animals that are of “aesthetic, ecological, educational, historical, recreational and scientific value.” It also protects the listed species’ “critical habitat”, the geographic area occupied by, or essential to, the protected species. The U.S. Fish and Wildlife Service (USFWS) and the National Marine Fisheries Service (NMFS) share authority to list endangered species, determine critical habitat and develop recovery plans for listed species. Currently, approximately 830 animals and 270 plants are listed as endangered or threatened nationwide at Title 50, Part 17, sections 11 and 12 of the Code of Federal Regulations. Further, under a settlement with environmental groups, USFWS has agreed to propose listing another 400 species over the next few years. A number of endangered or threatened species are found in Riverside County. These include least bell's vireos, southwestern willow flycatchers, California gnatcatchers, Stephen’s' and San Bernardino kangaroo rats, quino checker spot butterflies, arroyo toads and Delhi sands flower-loving flies.

Ephemeral Stream – A stream or part of a stream that flows only in direct response to precipitation; it receives little or no water from springs, melting snow, or other sources; its channel is at all times above the water table.

Evapotranspiration – The process by which water is discharged to the atmosphere as a result of evaporation from the soil and surface-water bodies, and transpiration by plants. Transpiration is the process by which water passes through living organisms, primarily plants, into the atmosphere.


Fast Tract Project – A streamlined land-use approval and permit process, saving qualified businesses precious time and money through expeditious processing of commercial and industrial projects. To qualify the project must create a minimum of 75 permanent full-time jobs, invest a total of at least $10 million in land, buildings and/or equipment or produce $25 million in taxable annual sales. The process allows developers to meet with County and District Subdivisions Staff prior to official submittal of the project to the County. This process allows the developers to identify and correct for potential constraints on their developments prior to their first submittal. Once a project is qualified and is submitted under the Fast Track process, it is guaranteed expedited review from the various County Agencies.

Fee – Real property owned outright by title, generally without any limitations or restrictions (also known as Fee Simple), but subject to the limitations of eminent domain, police power and taxation.

Federal Emergency Management Agency (FEMA) – administers the NFIP and disaster planning and recovery programs. FEMA works closely with states and communities and provides financial and technical assistance and flood hazards maps and data to better manage floodplains.

Field Density Test – Determines the density of a compacted fill to see if it meets predefined specifications. The District performs Field Density Tests using a nuclear gauge. The device has a probe containing a radioactive material that is inserted into a hole punched into the compacted soil. The rate of radiation penetration through the soil is detected and used to determine both the wet density and water content of the soil. The dry density can then be calculated and compared to the maximum dry density obtained by previous soils testing (most likely from the modified proctor test).

Flight Height – is defined as the height of the camera above the mean ground elevation. Photogrammetric mapping requires that a certain ratio of flight height to contour interval be maintained in order to assure minimum accuracy of the mapping. Flight Line – A line drawn on a map or chart to represent the track of the aircraft during the period taking aerial photographs.

Flood Insurance Rate Map (FIRM) – A FIRM is the official map of a community on which FEMA, the Federal Emergency Management Agency, has delineated both the special flood hazard areas and the flood risk premium zones applicable to the community. The base maps are usually USGS 7.5- Minute Quadrangles and can be found in the floodplain management section. Flood risk information presented on FIRMs is based on historic, meteorologic, hydrologic, and hydraulic data, as well as open-space conditions, flood control works, and development. To prepare FIRMs that illustrate the extent of flood hazard in a flood prone community, FEMA conducts engineering studies referred to as Flood Insurance Studies (FISs). Using information gathered in these studies, FEMA engineers and cartographers delineate Special Flood Hazard Areas (SFHAs) on FIRMs. SFHAs are those areas subject to inundation by a flood that has a 1-percent or greater chance of being equaled or exceeded during any given year. This type of flood is referred to as a base flood. A base flood has a 26-percent chance of occurring during a 30-year period ... the length of many mortgages. The base flood is a regulatory standard used by Federal agencies, and most states, to administer floodplain management programs, and is also used by the National Flood Insurance Program as the basis for insurance requirements nationwide.

Flood Insurance Studies (FIS) – Flood hazard areas are determined using statistical analyses of records of river-flow, storm tides, and rainfall; information obtained through consultation with the community; floodplain topographic surveys; and hydrologic and hydraulic analyses. The FIS covers those areas subject to flooding from rivers and streams, along coastal areas and lake shores, or shallow flooding areas. Actual copies of FISs can be ordered from FEMA’s Map Services Center. The results of the Flood Insurance Study that define flood risk areas for each community are available in a technical document that provides information used for floodplain management. This is known as the Flood Insurance Study Report. Regulatory floodways and other floodplain management information may be shown on a separate flood map known as a Flood Boundary and Floodway Map (FBFM). If the FBFM for the FIS is available, it is distributed with the Flood Insurance Study report. Floodplain: The relatively flat area of low lands adjoining, and including, the channel of a river, stream, watercourse, bay, or other body of water which is subject to inundation by the flood waters of the 100-year frequency floods. Floodway - The channel of a river or other watercourse and the adjacent land areas that must be reserved in order to pass the 100-year flood without cumulatively increasing the water surface elevation more than one foot. The floodway also includes all land necessary to convey a ten-year flood without structural improvements. Private development may not encroach into floodway limits without construction of a FEMA approved flood control facility that is to be maintained by a public agency and without first obtaining a CLOMR.

Freeboard – Generally defined as the difference in elevation from the top edge of a flood control facility (channel, dam, basin) to the design WSE. Freeboard provides a factor of safety and protects against unknown factors such as wave action. Freeboard varies based on the type of project and velocities of flows, but is generally between 1-3 feet.

Frequency Analysis – a statistical technique used by hydrologists for estimating the average rate at which floods, droughts, storms, stores, rainfall events, etc., of a specified magnitude recur. The District generally performs frequency analysis on rainfall data.


General Plan – The general plan is the master document for planning for growth in the city or region. In California, state law requires all cities and counties to adopt "a comprehensive, long-term general plan for [its] physical development." This general plan is the official city or county policy regarding the location of housing, business, industry, roads, parks, and other land uses, protection of the public from noise and other environmental hazards, and for the conservation of natural resources. The legislative body of each city (the city council) and each county (the board of supervisors) adopts zoning, subdivision and other ordinances to regulate land uses and to carry out the policies of its general plan. The local general plan can be described as the city's or county's "blueprint" for future development. It represents the community's view of its future; a constitution made up of goals and policies upon which the city council, board of supervisors, and planning commission will base their land use decisions. The general plan is not the same as zoning. Although both designate how land may be developed, they do so in different ways. The general plan and its diagrams have a long-term outlook, identifying the types of development that will be allowed, the spatial relationships among land uses, and the general pattern for future development and infrastructure. Zoning regulates present development through specific standards such as lot size, building setback, parking and landscaping requirements and a list of allowable uses. Development must not only meet the specific requirements of the zoning ordinance but also the broader policies set forth in the local general plan.

General Provisions – The portion of the Specification and Contract Document that defines the relationship between the District and the Contractor. It defines those items that tend to be common to all construction project contracts. These items include the scope of work, the authority and responsibilities of the parties, the responsibility for supplying materials, legal relations, expected progress, insurance requirements and guidelines for payment for work.

GPS Surveys – Global Positioning System (GPS) Surveys are based on a one-way (Satellite to receiver) ranging system. GPS surveys are fast and accurate. They also require expensive equipment and are dependent on satellite availability/visibility. There are two types of GPS surveys – Standalone navigational mode surveys – which provide an accuracy of +/-2 to 10 meters (similar to retail hand held units); and differential or relative positioning surveys which yields centimeter accuracies. In differential surveys, two GPS units are required. One unit is placed on a known control point, or benchmark, the other is placed on points where coordinating information is required. The District uses various types of differential units, including RTK, data logging and kinematic GPS units, to determine the coordinates of unknown points quickly and accurately. Points can often be located with differential units in a matter of seconds.


Hydraulic Analysis – The analysis undertaken to determine the capacity of a particular drainage work. This analysis is used to determine the attributes of the flowing water such as, water level or surface profile, velocity, total energy and erosive force (tractive force).

Hydraulic Grade Line – The hydraulic grade line is defined as the static head of water. For storm drains under pressure flow, it can be represented by the height relative to the invert of the storm drain to which water would rise if a tube were inserted in the storm drain soffit. Hydrograph - A hydrograph is a graph that shows changes in discharge of a river or stream at a given point over time. The time scale may be in minutes, hours, days, months, years or decades.

Hydrologic soil group – A classification of a soil type on the basis of its permeability after prior wetting and swelling of the soil, and without the protective effect of vegetation.

Hydrology – Science dealing with the occurrence, distribution and circulation of water on the earth, including precipitation, storm water runoff and groundwater.

Hyetograph – A graph of precipitation over time. The District has three standard hyetographs that are used for hydrologic analysis. The hyetographs represent precipitation patterns for 3-hour, 6-hour and 24-hour duration rainfall events.


Illicit Discharge – is any discharge to a municipal separate storm sewer that is not composed entirely of storm water except discharges pursuant to a NPDES permit (other than the NPDES permit for discharges from the municipal separate storm sewer) and discharges resulting from fire fighting activities.

Impervious Surface – Surface that prevents or significantly reduces the entry of water into the underlying soil, resulting in runoff from the surface in greater quantities and/or at an increased rate when compared to natural conditions prior to development. Examples of places that commonly exhibit impervious surfaces include parking lots, driveways, roadways, storage areas, and rooftops. The imperviousness of these areas commonly results from paving, compacted gravel, compacted earth, and oiled earth.

Invert – Generally considered to be the lowest point on a channel or storm drain.

Isohyetal Maps – A map describing the expected precipitation over an area based on a given return frequency. Each isohyet, or line, represents a line of equal precipitation. By identifying your location on a map and determining the magnitude of the adjacent isohyets, you can determine the magnitude of rainfall expected to occur during a specific return frequency. The District hydrology manual provides isohyetal maps for 2 year and 100 year return frequencies.


Jetting – In jetting, water is pumped under pressure through a steel tube into a soil. The force of the jetted water moves and compacts the bedding or backfill material below it. A sand material with few fines can be jetted to produce good compaction, especially under pipe haunches or other areas that are difficult to mechanically compact. The sand material must be clean and free draining and the surrounding soil must be well drained, or other means of draining the backfill must be provided. As with any type of backfilling, material should be placed slowly and in lifts. Jetted lifts can be places as thick as 4 feet. It should only be practiced when the proper soils are available and mechanical compaction is not feasible. Jetting is controversial. It is often difficult to guarantee consistent compaction with the jetting process.



Lateral Pipe – A small, usually reinforced concrete pipe, which conveys water from catch basins or other inlets, to the mainline storm drain or channel.

Land Use Permits – These are permits obtained for particular development proposals on already subdivided land. The zoning of the site determines the types of uses allowed and the appropriate type of application for that use to be filed with the Planning Department. Common use cases are: Conditional Use Permits, Second Unit Permits, Public Use Permits, Plot Plans subject to the California Environmental Quality Act (CEQA), and Plot Plans that aren’t subject to CEQA. Each type of permit has different requirements for its public hearing process, the use of the permit and the revocation of the permit.

Legal Description – The description portion of the limit of real property in any deed, trust deed, or other title document. It must be approved by an individual authorized to practice land surveying. The creation and recording of legal descriptions are regulated by the Professional Land Surveyor’s Act.

Letter of Map Revision (LOMR) – Issued by FEMA with an accompanying copy of an annotated FIRM, this acknowledges changes in the base flood elevation, floodplain boundary, or floodway based on post-construction or revised conditions. LOMRs are issued upon completion of a project. Most projects obtain a CLOMR prior to construction to ensure that the proposed facility will meet FEMA criteria. Obtaining a CLOMR is a way to guarantee that unforeseen issues do not prevent the issuance of a LOMR.

Levee – An elevated berm that is used to protect adjacent low lying ground from floodwaters. The levee is usually lined with a structural material such as concrete or rip-rap to ensure that it does not fail from erosion. This lining usually extends many feet below ground to ensure that scour caused by high water velocities cannot undermine the levee.


Manhole – An opening in the top of a storm drain that allows access to the storm drain from the manhole inlet (usually located in the street). Manholes are significant because they introduce hydraulic inefficiencies into the storm drain system.

Manning's Equation – A formula for calculating the velocity of flow in a channel as a function of relative roughness, cross-sectional configuration, and gradient.

Master Drainage Plan (MDP) – A master drainage plan addresses the current and future drainage needs of a given community. The boundary of the plan usually follows regional watershed limits. The proposed facilities may include channels, storm drains, levees, basins, dams, wetlands or any other conveyance capable of economically relieving flooding problems within the plan area. The plan includes an estimate of facility capacity, sizes and costs. Preparation of an MDP requires not only an understanding of the existing flood hazards, but also an understanding of the future development trends within a community. Planning engineers must obtain the latest County and/or city General Plans to establish the ultimate development pattern for the plan area. Once this is known, the Planning engineer can estimate future runoff patterns and prepare a plan that economically addresses both existing and future problems. MDP’s are prepared for a variety of purposes. First, the plans provide a guide for the orderly development of the County. Second, they provide an estimate of costs to resolve flooding issues within a community. These plans are used by the District’s Management, Zone Commissioners and Board of Supervisors to determine Capital Project expenditures for each budget year. Finally, the plans can be used to establish Area Drainage Plan fees for a given community, which prevent existing taxpayers from having to shoulder the burden of land development costs.

Maximum Extent Practicable (MEP) – Maximum Extent Practicable (MEP) is the technology-based standard established by Congress in the CWA that municipal dischargers of storm water (MS4s) must meet. Technology-based standards establish the level of pollutant reductions that dischargers must achieve, typically by treatment or by a combination of treatment and best management practices (BMPs). MEP generally emphasizes pollution prevention and source control BMPs primarily (as the first line of defense) in combination with treatment methods serving as a backup (additional line of defense). MEP considers economics and is generally, but not necessarily, less stringent than BAT. A definition for MEP is not provided either in the statute or in the regulations. Instead the definition of MEP is dynamic and will be defined by the following process over time: municipalities propose their definition of MEP by way of their Urban Runoff Management Plan. Their total collective and individual activities conducted pursuant to the Urban Runoff Management Plan becomes their proposal for MEP as it applies both to their overall effort, as well as to specific activities (e.g., MEP for street sweeping, or MEP for municipal separate storm sewer system maintenance). In the absence of a proposal acceptable to the RWQCB, the RWQCB defines MEP.

Migratory Bird Rule – The Army Corps of Engineers has broadened the commerce definition of Waters of the United States to include ephemeral streams and wetlands by incorporating the “Migratory Bird Rule”. This rule states that any water or wetland that may support migratory birds by default supports interstate commerce due to hunting, bird watching and camping activities that occur along migratory bird routes. This interpretation provides the nexus that allows the USACE to regulate these water bodies.

Mitigation Fee – A fee, also called a development fee, levied on the developer of a project by a city, county or other public agency as compensation for otherwise-unmitigated impacts the project will produce. California Government Code Section 66000, et. seq., specifies that development fees shall not exceed the estimated reasonable costs of providing the service for which the fee is charges. To lawfully impose a mitigation fee, the public agency must verify its method of calculation and document proper restrictions on use of the fund.

Modified Proctor Test – A compaction test that attempts to determine the maximum possible density of a soil by performing a series of test on a compacted sample of the soil. For each test, the amount of water present in the sample at the time of compaction is varied. A plot of the results, comparing water content (horizontal axis) to relative dry density (vertical axis) is then made. The plot usually resembles a bell curve. The plot provides the maximum possible dry density achievable by the soil and the optimum water content necessary to achieve that density. Results of the Modified Proctor test are used by contractors to determine the proper range of water content of the fill necessary to meet the District’s specified compaction requirements. Modified Proctor Tests are usually performed by a soils engineer many months before construction begins. Field Density tests are used to compare Densities achieved in the field to the theoretically maximum density determined by the Modified Proctor Test.

Municipal Separate Storm Sewer System (MS4) – A MS4 is a conveyance or system of conveyances (including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, natural drainage features or channels, modified natural channels, man-made channels, or storm drains): (i) Owned or operated by a State, city town, borough, county, parish, district, association, or other public body (created by or pursuant to State law) having jurisdiction over disposal of sewage, industrial wastes, storm water, or other wastes, including special districts under State law such as a sewer district, flood control district or drainage district, or similar entity, or an Indian tribe or an authorized Indian tribal organization, or designated and approved management agency under section 208 of the CWA that discharges to waters of the United States; (ii) Designated or used for collecting of conveying storm water; (iii) Which is not a combined sewer; (iv) Which is not part of the Publicly Owned Treatment Works (POTW). Historic and current development makes use of natural drainage patterns and features as conveyances for urban runoff. Urban streams used in this manner are part of the municipalities MS4 regardless of whether they are natural, man-made, or partially modified features. In these cases, the urban stream is both an MS4 and a receiving water.


National Flood Insurance Program (NFIP) – In 1968, Congress created the NFIP in response to the rising cost of taxpayer funded disaster relief for flood victims and the increasing amount of damage due to floods. The program is designed to reduce the loss of life, damage to property and rising disaster relief costs in these high-risk areas. The NFIP makes federally backed flood insurance available to communities that agree to adopt and enforce floodplain management ordinances intended to reduce future flood damage. This voluntary program is administered by FEMA and aims to end the expensive cycle of flooding and rebuilding. National Flood Insurance is available in more than 19,000 communities across the United States and its territories. The program required that new or replacement buildings in the flood hazard areas are constructed to mitigate future flood damages. FEMA insists on assurances that local upstream flood repair measures and development within floodplains will not exacerbate flooding in adjacent areas. It guides future development away from flood prone areas and transfers the costs of flood losses from American taxpayers to floodplain property owners. The NFIP, through partnerships with communities, the insurance agencies and the lending industry, helps to reduce flooding damages by nearly $800 million a year. Further, buildings constructed in compliance with NFIP standards suffer approximately 80% less damage annual than those not built in compliance. Every $3 paid in flood insurance claims saves $1 in disaster assistance payments. THE NFIP program is made of three components: Flood Insurance, Mapping and Floodplain Management. The NFIP is managed by FEMA’s Federal Insurance and Mitigation Administration and the Mitigation Directorate. The Federal Insurance and Mitigation Administration manages the insurance component of the NFIP. The Mitigation Directorate overseas the floodplain management and mapping components of the program.

National Geodetic Vertical Datum of 1929 (NGVD29) and North American Vertical Datum of 1988 (NAVD88) – Two vertical control datums for the North American Continent. The Datums are referenced to mean sea level. NGVD29 was based on sea level measurements and leveling networks along the coast, NAVD88 was based on gravity measurements and uses the Great Lakes to determine sea level. They are completely different datums, based on slightly different ellipsoid models of the earth. The difference between models produces slightly different elevations at any given point on the surface of the earth. It is very important to understand which vertical datum your survey information is based on. The elevation difference between the datums is generally less than 2.5 feet in Riverside County. Many engineers have had to make costly changes to their design during construction because they hadn’t noticed that a plan set they had based a design on was on a different vertical datum than the rest of the project.

National Environmental Policy Act (NEPA) – The federal law, adopted in 1969, that provided the model for CEQA. The law requires that agencies make a diligent effort to involve the public in the project planning process. The law requires the preparation of an Environmental Assessment (EA) to determine if the proposed project will have any adverse environmental impacts. Upon completion of the EA, a Finding of No Significant Impacts (FONSI) may be filed if no impacts are found. An Environmental Impact Statement (EIS), which analyzes the project’s impacts and potential mitigation measures, must be prepared if significant impacts to the environment are found. Both documents must be made available for public review. Upon completion of the noticing/review period, any necessary changes to the project and/or documents are made by the lead agency and a Record of Decision (ROD) can be filed authorizing the project as described in the revised documents. NEPA regulations must be followed when a project is constructed on federal lands, is constructed with federal funds, or is found to be regulated by other federal environmental regulatory laws. The federal agencies undertaking or funding the project are responsible for ensuring that the project complies with NEPA.

National Pollution Discharge Elimination System (NPDES) – The national program for issuing, modifying, revoking and reissuing, terminating, monitoring, and enforcing permits, and imposing and enforcing pretreatment requirements, under sections 307, 402, 318, and 405 of the Clean Water Act. NPDES permits pertain to the discharge of waste to surface waters. All State and Federal NPDES permits are also Waste Discharge Requirements (WDRs).

Non Point Source (NPS) – refers to diffuse, widespread sources of pollution. These sources may be large or small, but are generally numerous throughout a watershed. Non Point Sources include but are not limited to urban, agricultural, or industrial areas, roads, highways, construction sites, communities served by septic systems, recreational boating activities, timber harvesting, mining, livestock grazing, as well as physical changes to stream channels, and habitat degradation. NPS pollution can occur year round any time rainfall, snowmelt, irrigation, or any other source of water runs over land or through the ground, picks up pollutants from these numerous, diffuse sources and deposits them into rivers, lakes, and coastal waters or introduces them into ground water. Non-Structural Floodplain Management Controls – Management controls that prevent structures from impacting floodplains. Zoning ordinances that limit developments within mapped floodplains are the most common non-structural control. Other controls include designating low-lying areas and wetlands as overflow areas that for storing excessive floodwaters and/or relocating residents located within mapped floodplains. These techniques are often viable in developing areas or rural areas, but can be very controversial in highly urbanized areas.

North American Datum (NAD) – The horizontal control datum for the North American Continent. It was first established in 1927 (NAD27) by geodetic surveying methods, using Meades Ranch in Kansas as its base position. A new datum was established in 1983, based on a more accurate geodetic model of the earth’s surface (NAD83). NAD83 coordinate points cannot be directly interchanged with NAD27 coordinate points. Both datums refer to the x coordinate as an “Easting” and the y coordinate as a “Northing”. Coordinates increase as you head east and north.


Ordinance 458 – The purpose of the ordinance is to protect public health and safety, public welfare and minimize public and private costs caused by flooding by regulating development within flood hazard areas. This ordinance was adopted to meet the criteria of the National Flood Insurance Program and proposes regulations that meet the requirements of the program. The ordinance regulates FEMA mapped floodplains as well as specified non-FEMA mapped floodplains (Ordinance 458 Floodplains).

Orthophoto Mapping – The District’s general purpose mapping. Usually plotted at a scale of 1”=200’ or 1”=400’. The maps have a contour interval of 4 feet. The maps cover a one square mile area and are indexed to the U.S. Rectangular Survey System (Township/Range/Section system). The maps generally identify contours, stream courses and known survey control points.

Orthophotograph – A photographic copy, prepared from a perspective photograph, in which the displacements of images due to tilt and relief have been removed.


Perennial stream – A stream that normally has water in its channel at all times.

Photogrammetry –The science of obtaining reliable measurements by photography. The District uses stereoscopic photographic methods to generate maps. The stereoscopic method uses binocular vision to form a single three-dimensional image from two photographic images of the same terrain taken from slightly different vantage points. With proper optical or digital equipment, all measurements needed in map construction can be made from this visual model. The digital stereoscopic technology is similar to the 3d technology that IMAX theatres use to make and present 3D movies.

Photogrammetric Surveys – Photogrammetric surveys are conducted using aerial photography and ground survey control. Surveyors establish initial ground control that can be identified from the aerial photographs taken at high altitude by specialized aircraft. The control is used to correct for edge distortions in the photographs. Photogrammetric surveys are used to accurately and quickly map large tracts of land. Photogrammetric methods allow for faster compilation of data, but can provide inaccurate results in areas with dense cover and extremely flat terrain. These areas may need to be supplemented with additional total station or GPS survey data.

Planimetrics – mapping features for which only horizontal data is presented. These features generally include property lines, street centerlines, structure footprints, utility lines, location of vegetation and other natural or cultural features that may be pertinent to the purpose of the map.

Point Source – is any discernible, confined, and discrete conveyance, including, but not limited to, any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated animal feeding operations, landfill leachate collection systems, vessel, or other floating craft from which pollutants are or may be discharged.

Pollutant – is broadly defined as any agent that may cause or contribute to the degradation of water quality such that a condition of pollution or contamination is created or aggravated. Under Clean Water Act (CWA) Section 502(6) a pollutant is defined as dredged spoil, solid waste, incinerator residue, sewage, garbage, sewage sludge, munitions, chemical wastes, biological materials, radioactive materials, heat, wrecked or discarded equipment, rock, sand, cellar dirt, and industrial, municipal, and agricultural waste discharged into water.

Pollution – as defined in the Porter-Cologne Water Quality Control Act, pollution is “the alteration of the quality of the waters of the State by waste, to a degree that unreasonably affects the either of the following: (1) The waters for beneficial uses; or (2) Facilities that serve these beneficial uses.” Pollution may include contamination.

Porter-Cologne Water Quality Control Act – also referred to as the ‘Porter-Cologne Act’. It is the principle law governing water quality regulation in California. It is the policy of the state, as set forth in Porter-Cologne, that the quality of all the waters of the state shall be protected, that all activities and factors affecting the quality of water shall be regulated to attain the highest water quality within reason, and that the state must be prepared to exercise its full power and jurisdiction to protect the quality of water in the state from degradation. Porter-Cologne directs the State Water Resources Control Board to formulate and adopt state policies for controlling water quality and designates the State Board as the state water pollution control agency for all purposes stated in the Clean Water Act. Porter-Cologne establishes the policies that are to be implemented and authorities that are to be used in achieving the goals of the Clean Water Act.

Post-Construction BMPs – are a subset of BMPs including structural and non-structural controls which detain, retain, filter, or educate to prevent the release of pollutants to surface waters during the final functional life of development.

Professional Land Surveyor’s Act – In 1891, the State of California became the first state to license Professional Land Surveyors. The Board for Professional Engineers and Land Surveyors administers the current version of the Professional Land Surveyors Act (PLSA) defining the scope of practice and license requirements for professional land surveyors. The PLSA is revised periodically by the legislature to ensure the protection of the public health, safety and welfare and to reflect changes in technological advancements and licensure requirements based on economic, social, and political conditions. The Act regulates the profession of surveying and defines how various types of surveys are to be undertaken and recorded.



Rational Method – A means of computing flow rates (Q) by use of the formula Q = CIA, where C is a coefficient describing the physical drainage area, I is the rainfall intensity and A is the area. The method is easy to apply and works well on small watersheds. It is generally not suited for the analysis of watersheds over 300 acres in size.

Record of Survey – A legal record of a survey undertaken to establish or reestablish land boundaries or property boundaries. Every survey relating to land boundaries or property lines by a professional land surveyor using existing township plats or notes, subdivision maps, official maps, or records of survey that discloses a discrepancy with an existing record of survey or establishes a new point or line for a parcel in a property description that is not shown on another record of survey, must file a record of survey with the County Surveyor within 90 days after completion of the survey.

Reinforced Concrete – A composite material made of concrete and steel. Steel is placed inside the concrete structure in areas where the structure will be exposed to tensile forces. It is generally more economical to use reinforced concrete to offset the tensile forces than it is to design an entirely concrete or steel section capable of resisting the compressive/tensile forces. The reinforced concrete structure must be carefully designed to ensure that the materials act as a single composite material.

Reinforced Concrete Pipe (RCP) – A storm drain construction method using pre-cast sections of pipe that are delivered to a site. The sections, usually 8 feet long, are linked together in the pipe trench to form a continuous storm drain system.

Relative Compaction – This is the ratio of field dry density test results to the theoretical maximum dry density test results obtained by a Modified Proctor Test. District design engineers specify a minimum relative compaction to be achieved by a contractor during placement of the fill. The specified Relative Compaction can vary based on the type of fill being placed. Relative compaction specification can vary with the type of fill. Examples include sub grade (90%), over excavation fill (90%), or dam embankment (95%).

Return Frequency – A measure of how often (on average) an event (precipitation, flood, etc.) will occur that is greater than some chosen value (100 year, 10 year, 5 year, etc); the inverse of the exceedance probability.

Right of Way – Any strip or area of land, including surface, overhead, or underground, granted by deed or easement, for construction or maintenance according to designated use, such as for drainage channels, storm drains, flowage easements or impoundment of surface water.

Routing – A type of hydrologic analysis used to determine the reduction in the peak flow caused by friction losses and storage in a stream channel or reservoir. It is determined by mathematically modeling the passage of the hydrograph through the stream channel or reservoir over time.

Runoff – Surface water flow that is generated from a rainfall event. The amount of runoff generated is generally a function of the amount of rainfall, the permeability of the soils, ground cover and the amount of land development. Many other factors can also influence the amount of runoff including the size of the watershed, the sequence of storms within the watershed (are soils already saturated from previous rainfall?), evapotranspiration, and terrain type.


Section 7 Consultation – Section 7 of the federal Endangered Species Act requires federal agencies to insure that actions they authorize, fund, or carry out are not likely to jeopardize the continued existence of threatened or endangered species or result in the destruction or adverse modification of critical habitat for these species. The U. S. Fish and Wildlife Service (FWS) and National Marine Fisheries Service (NMFS) share responsibilities for administering the Act and performing the Section 7 Consultation. The opinion issued at the conclusion of consultation with FWS/NMFS will include a statement either authorizing the take of any habitat or species that may occur incidental to an otherwise legal activity or denying the activity because, as proposed, it would put the continued existence of the species in jeopardy (known as a jeopardy finding). The District usually enters Section 7 Consultations as part of the CWA Section 404 permitting process with the United States Army Corps of Engineers.

Section 18 – That portion of the District’s enabling act (passed in 1945) requiring a public hearing before any project or plan may be undertaken by the District. The Act requires that the Board of Supervisors authorize a Notice of Intention for the District project or plan, which must to be publicly advertised. After 30 days, the Board of Supervisors can hold a public hearing on the project. If the Board receives a written protest from the majority of registered voters within the District’s Zone containing the project, the Board may not proceed with the project.

Section 401 Permit – Section 401 of the Clean Water Act requires that a state (California) must certify that federal licenses or permits which may result in a pollutant discharge into navigable waters (i.e. a Section 404 Permit) meet state water quality standards (including NPDES standards). The state may certify, condition or deny the proposed activity. If the state conditions the activity, those conditions must be incorporated into the Section 404 permit. In California, the Regional Water Quality Control Boards are responsible for issuing the Section 401 Water Quality Certifications.

Section 404 Permit – Under Section 404 of the Clean Water Act, a permit is required from the United States Army Corps of Engineers (USACE) for the discharge of dredged or fill material into Waters of the United States (including wetlands). Guidelines for implementation of the permit are referred to as the Section 404 (b)(1) Guidelines and were developed by the Environmental Protection Agency (EPA) in conjunction with USACE. Under the USACE guidelines, any activity that disturbs wetlands areas, including flood control maintenance activities and construction of flood control facilities in Waters of the United States, can be construed as requiring a Section 404 permit. The Guidelines allow the discharge of dredged or fill material into the aquatic system only if there is no practicable alternative that would have less adverse impacts. Adverse impacts can be offset through mitigation. Mitigation commonly takes the form of the purchase of nearby lands that can be made to function as wetlands, thereby offsetting the areas disturbed by the discharge of dredged or fill materials. Section 404 also requires that federal guidelines for water quality (Section 401 Water Quality Certificate) and Endangered Species Act requirements (Section 7 Consultation) be met prior to the issuance of the permit.

Section 1601 Streambed Alteration Permit – Under this section of the Fish and Game Code, public agencies are required to notify the California Department of Fish and Game (CDFG) prior to any project that would divert, obstruct or change the natural flow, bed, channel, or bank of any river, stream, or lake. Preliminary notification and project review generally occurs during the environmental process. When an existing fish or wildlife resource may be substantially adversely affected, CDFG is required to propose reasonable project changes to protect the resource. These modifications are formalized in a Streambed Alteration Agreement that becomes part of the plans, specifications and bid documents for the project.

Separate Application – An application for development within a FEMA mapped floodplain or an Ordinance 458 floodplain. This application is required for developments that are not otherwise conditioned to meet floodplain ordinances through the usual land division process or that are not covered by other ordinances. Special Applications are generally required for projects that can be approved through grading or building permit only. These projects include things like construction or remodeling of a single custom home on an existing lot.

Soffit – The highest point of the interior of the storm drain pipe.

Soils Compaction – The densification of soils by the application of energy, usually mechanical energy (mechanical compaction). Soils are compacted to increase stability, enhance resistance to erosion, decrease permeability and decrease compressibility. This is usually accomplished by placing the soil in shallow lifts (layers) up to eight inches thick, then using heavy mechanical equipment to compress the lifts. The equipment usually applies energy to the soil by static loading, impact, vibration or kneading action. The type of compaction depends on the type of soil and the purpose of the soil compaction.

Soils Investigation – An investigation of the geotechnical characteristics of the project site. The District usually enters contracts for geotechnical work with private geotechnical firms. Geotechnical studies vary with the objective of the project, but are generally accomplished by taking samples from soils borings or trenches. Soils investigations usually provide guidelines for temporary excavations, for suitability of soils for pipe bedding and trench backfill and for various soils design parameters such as allowable bearing pressure and lateral earth pressure. Soils investigations are also used to assess the suitability of soils for special construction techniques such as Cast-In-Place-Pipe (CIPP) placement.

Special Provisions – This portion of the Specification and Contract Document covers those items of the contract between the District and the Contractor that are unique to this project. They include items such as the expected time of completion, site maintenance, work hours, any encroachment permits or interagency agreements that the contractor must abide by and any special state or federal requirements that the contractor must abide by. Other items could include minimum notification times required to obtain the services of a District Surveying team, required disposal sites for excess materials or contaminated materials and location of project signs. It could also specify the authority of the District to select from multiple construction options for a particular portion of the project by some predefined point in time during the construction process.

Special Flood Hazard Areas (SFHA) – A darkly shaded area on a FIRM or Flood Hazard Boundary Map, FHBM, identifying an area with a one percent chance of being flooded in any given year; hence the property is in the 100- year floodplain.

Specifications and Contract Document – This document is prepared by the Project Engineer in the Design Engineering Section. The Document is a complete description of the project to be constructed, including contractual obligations of the District and Contractor as well as the estimated time, costs, and methods and materials of construction to be used. It contains the general provisions, the special provisions, the detailed specifications and the drawings (plans) that detail the project to be constructed. This document is used by contractors interested in bidding on the project to determine their probable cost of construction, it is used by the inspectors to police and control the project construction and it is used by the surveyors to place the survey control necessary to align and construct the project.

Stage – The river stage is the height of the water in the river, measured relative to an arbitrary fixed point.

Standard Plans – Details of standard structures, devices or instructions referred to on the Plans or in the Specifications, usually by title or number. Standard Plans are plans for structures that are commonly constructed in a way that can be described generically. Examples of structures that have “standard plans” are catch basins, channel sections and street sections. There are many different sources of standard plans. The District has a set of Standard Plans for Drainage Structures. CalTrans has a set of Standard Plans for Freeway Construction (which also includes some standards for drainage structures), the Public Works Standards Association also produces a set of Standard Plans for general construction project items. Depending on the structure and location, the District can and does reference several of these Standard Plans in the Specification and Contract Documents. It is not uncommon, though, that District projects will require modifications or abandonment of a standard plan due to site constraints. In these cases, the District’s Design Engineers will create and specify a specific design for that particular structure.

Standard Specifications for Public Works Construction – Commonly referred to as the “Greenbook”, or “Standard Specifications” this document was originally published in 1967. The last 10 editions were produced by a joint committee of the Southern California Chapter of the American Public Works Association and the Southern California Districts of the Associated General Contractors of California. Since 1996, the manual has been produced by the Public Works Standards, Inc., a corporation headed by members of a number of public works associations. The book provides standard language for the general provisions of contract documents; standard criteria and testing methods for construction materials and standards for construction methods. The District generally references these standards in our Specifications and Contract Documents.

Standard Specifications of the State of California, Department of Transportation – Commonly referred to as “State Standard Specifications”, this manual is prepared by Caltrans. It provides alternative, but similar, standards for construction methods and materials. The District usually references the State Standard Specifications when we are constructing projects that are within Caltrans Rights of Way or when we use Caltrans Standard Plans for the design of specific facilities (i.e. reinforced concrete box). State Plane Coordinate Systems – A plane-rectangular coordinate system established by the United States Coast and Geodetic Survey, one established for each state, used for converting position on the earth’s curved surface to planar x and y coordinates. The system allows surveyors to use plane surveying methods over great distances. The system in each state is divided into zones. Riverside County is in Zone VI of the California Coordinate System. The x and y coordinate points are generally referenced to a geodetic horizontal datum known as the North American Datum (NAD).

Storm Drain – An underground pipe used to convey runoff from urban areas to an adequate outlet. An adequate outlet can be a connection to a larger flood control facility or an outlet into an existing watercourse, such as the Santa Ana River, that has adequate conveyance capacity for the flow tributary to it. Storm drains are usually designed using specialized hydraulic software such as WSPGW. Analysis of storm drain capacity requires knowledge or estimation of downstream and/or upstream water surface elevations, material type, pipe slopes and diameter, inlet locations and flow rates.

Storm Water – is as defined urban runoff and snowmelt runoff consisting only of those discharges which originate from precipitation events. Storm water is that portion of precipitation that flows across a surface to the storm drain system or receiving waters. Examples of this phenomenon include: the water that flows off a building’s roof when it rains (runoff from an impervious surface); the water that flows into streams when snow on the ground begins to melt (runoff from a semi-pervious surface); and the water that flows from a vegetated surface when rainfall is in excess of the rate at which it can infiltrate into the underlying soil (runoff from a pervious surface). When all factors are equal, runoff increases as the perviousness of a surface decreases. During precipitation events in urban areas, rain water picks up and transports pollutants through storm water conveyance systems, and ultimately to waters of the United States.

Storm Water Pollution Prevention Plan (SWPPP) – A plan required by and for which contents are specified in the State of California General Permit for Storm Water Discharges Associated with Industrial Activities, and the General Permit for Storm Water Discharges Associated with Construction Activities. The purpose of the plan is to help identify the sources of pollution that affect the quality of storm water discharges from a site and to describe and ensure the implementation of practices to reduce pollutants in storm water discharges.

Structural Floodplain Management Controls – The use of dams, levees, channels, storm drains or other flood control devices to confine and direct flows away from people and property. This has been the historically preferred method of protecting residents in urbanized floodplains.

Subcritical Flow – A flow condition where the velocity is less than the critical velocity and the depth is greater than the critical depth.

Supercritical Flow – A flow condition where the velocity is greater than the critical velocity and the depth is less than the critical depth.

Synthetic Unit Hydrograph Method – A method that estimates the amount and pattern of runoff due to a "unit" of rainfall flowing into the watershed over a certain period of time. The pattern is than factored according to the amount of rainfall that actually fell for the time period. These individual patterns are then added for each time step to get the cumulative hydrograph from each basin.

Specific Plan – A tool authorized by Government Code §65450 et seq. for the systematic implementation of the general plan for a defined smaller portion of a community's planning area. A specific plan must specify in detail the development standards and requirements relating to density, lot size and shape, sitting of buildings, setbacks, circulation, drainage, landscaping, architecture, water, sewer, public facilities, grading, open space, financing and any other element needed for proper development of the property.

Subdivision Map Act – gives the local agency the authority to regulate and control the design and improvement of the subdivisions within its jurisdiction. Each city/county must adopt an ordinance regulating and controlling subdivisions, in Riverside County it’s Ordinance 460. The Map Act sets forth certain mandates that must be followed for subdivision processing. It defines what tentative maps, final maps and parcel maps are. It establishes development rights. It establishes procedures for the filing of maps, review of maps, exaction of dedications, imposition of fees, posting of improvement securities, and monuments. A local agency may impose conditions on the subdivision process when the map act is silent.


Temporary Construction Easement – A temporary easement giving the District rights to use others property for a specified period of time. These easements are usually obtained to allow a District contractor to gain access to a work site, to provide additional work room during the construction process or to do minor grading on lands adjacent to District properties during construction.

Tentative Maps, Parcel Maps and Final Maps – Land is divided into any number of units of improved or unimproved land or any portion thereof, for the purpose of sale, lease, or financing, whether immediate or future. When under review subdivisions of land into five or more parcels (lots) are usually referred to as tentative tract maps and subdivisions into four or less lots are usually referred to as parcel maps. In Riverside County, these maps are approved, conditionally approved or disapproved by the either the Planning Commission or the Planning Director and that action is reported directly to the Board of Supervisors. The conditioned approvals detailed the developer's entitlements to develop and the requirements that the developer must meet to receive those entitlements. Recorded tentative tract maps are referred to as Final Maps and recorded parcel maps are referred to as Final Parcel Maps.

Time of Concentration — The time period necessary for surface runoff to reach the outlet of a watershed from the most hydraulically remote point in the tributary drainage area.

Total Maximum Daily Load (TMDL) – is the maximum amount of a pollutant that can be discharged into a water body from all sources (point and non-point) and still maintain water quality standards. Under Clean Water Act section 303(d), TMDLs must be developed for all water bodies that do not meet water quality standards after application of technology-based controls.

Total Station Surveys – Total Station surveys integrate theodolites, electronic distance measurement (EDM) and data recorders. They collect vertical and horizontal data in a single operation. Data recorders can record information in the field to take back to the office for processing. Data recorders can also be used to download previously determined data at the office for use in the field to stake out or field locate construction control points and boundaries.

Tulloch Rule – An interpretation of Section 404 of the Clean Water Act by the Army Corps of Engineers. The rule states that any activity in Waters of the United States that could produce “incidental fallback” can be construed as placing fill in Waters of the United States, an activity that is regulated under the Section 404 permitting process. The incidental fallback concept has been extended to dirt that may temporarily cling to the tracks of heavy equipment then “fall back” into the watercourse. This controversial interpretation has been used by the USACE to regulate maintenance activities and other actions that would not otherwise be regulated under the Section 404 process. The rule is currently being reviewed by the courts.


Urban Runoff – is defined as all flows in a storm water conveyance system and consists of the following components: (1) storm water (wet weather flows) and (2) non-storm water illicit discharges (dry weather flows).

U.S. Rectangular Survey System – This system was devised with the objective of locating, marking and fixing subdivisions “for all time”. The system divides land into tracts approximately 24 miles on a side based on meridians and parallels of latitude. The tracts are further subdivided into 16 townships, which are 6 miles on a side. The townships are then subdivided into 36 sections, approximately 1-mile square. Townships are labeled using a range and township number. The township number is related to its position north or south of the base parallel of latitude. The range number is relative to the base meridian. The Sections of each township and range are numbered beginning northeastern most corner and ending in the southeastern most section. For example, a property located in T4S R3W S36 of the San Bernardino Base Meridian could be located in the Township 4 rows South of the standard parallel, the Range 3 columns West of the base meridian (San Bernardino) in Section 36 (lower southeastern most section of township). The District’s orthophoto maps are referenced to the U.S. Rectangular Survey System. Property Descriptions also reference this system. Thomas Brother Guides often include U.S. Rectangular Survey System coordinates information on their map pages. This is a quick way to reference properties of interest to available District mapping.



Water Quality Objectives – are the numerical or narrative limits on constituents or characteristics of water designated to protect designated beneficial uses of the water. [California Water Code Section 13050 (h)]. California’s water quality objectives are established by the State and Regional Water Boards in the Water Quality Control Plans.

Water Surface Elevation (WSE) – The depth of flowing water, measured to a common datum (e.g. stream channel invert, sea level, etc.), at a prescribed location. Water Surface Elevation is also defined as the height of a channel (or storm drain) above mean sea level (or other datum) plus the height of the hydraulic grade line above the channel.

Waters of the United States – Waters of the United States can be broadly defined as navigable surface waters and all tributary surface waters to navigable surface waters. Waters of the United States are also considered to be all waters, which are currently used, were used in the past, or may be susceptible to use in interstate or foreign commerce, including all waters which are subject to the ebb and flow of the tide, including wetlands. Groundwater is not considered a Waters of the United States.

Watershed – (1) An area that, because of topographic slope, contributes water to a specified surface water drainage system, such as a stream or river. (2) All lands enclosed by a continuous hydrologic drainage divide and lying upslope from a specified point on a stream; a region or area bounded peripherally by a water parting and draining ultimately to a particular water course or body of water.

Wetlands – Wetlands are those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions (U.S. ACE 1987). Wetlands generally include (1) swamps, marshes, bogs, and similar areas; (2) lands that are transitional between terrestrial and aquatic systems where the water table is usually at or near the surface of the land and is covered by shallow water. For purposes of this classification, wetlands must have one or more of the following attributes: (1) at least periodically, the land predominantly supports hydrophytes (plants dependent on saturated soils or a water medium); (2) the substrate is predominantly undrained hydric soil; and (3) the substrate is nonsoil and is saturated with water or covered by shallow water at some time during the growing season of each year.




Z-Points – An identification system for survey monuments established by the District’s Surveyors. When a control point is established in the field, the District Surveyor’s place a survey monument and assign the monument a “Z” number, usually in the form of “Z-4532”. This number is logged in a database maintained by the District so that the surveyors can quickly retrieve information about the location and coordinates of the monument at a future date. District orthophoto and design maps generally show locations and coordinate data for survey monuments established by the District.

Zone – The District is divided into seven geographical zones with each zone being taxed separately. Monies raised in one zone must be spent in only that zone. Each zone is represented by three Zone Commissioners appointed by the District's Board to advise the Supervisors and District staff.

Zone Commissioners – Each zone is represented by three zone commissioners appointed by the District's Board to advise them and District staff. Commissioners represent their respective areas within the Zone. The Commissioners preside over their Zone’s Budget Hearings and Workshops, where they receive input from the public and discuss construction project priorities.