SEU Glossary

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Stormwater Assessment Glossary of Terms

Ad Valorem
A tax which is based on the value of the property.

A hydrologic unit consisting of a drainage system consisting of a stream or body of impounded surface water plus all tributaries.

Basin Master Plan
A comprehensive study of the physical characteristics of a drainage basin. A master plan identifies flooding and water quality problems (or level of service deficiencies) and recommends solutions through a stormwater improvement program.

Best Management Practices (BMPs)
Activities or structural improvements that help reduce the volume of stormwater and improve the quality of stormwater runoff. BMPs include treatment requirements, operating procedures, and practices to control site runoff, spillage or leaks, sludge or waste disposal or drainage from raw material storage.

A water quality practice that utilizes landscaping and soils to treat urban stormwater runoff by collecting it in shallow depressions. It then filters the runoff through a fabricated planting soil media. 

A schedule of large-scale projects to improve stormwater level of service deficiencies identified in the Basin Master Plan.

Capital Improvement Assessment
In order to fund capital improvement projects, as identified in the Basin Master Plans, an assessment is levied on parcels in basins where capital projects are to be constructed. This Capital Improvement assessment is in addition to the Service Assessment described above. Capital improvement assessments collected in a particular basin are used exclusively to fund capital projects within that basin. Basin Master Plans analyze the need for capital improvements in relation to established levels of service – structure flooding, street flooding, and water quality. Capital improvement assessments are calculated based on the project cost associated with a specified level of service and any related debt or financing cost and the total ESUs of the parcels within the improvement area. The capital assessment is levied according to the ESU count of a given parcel. Because the number and cost of projects varies in each basin, capital assessments vary between the basins.

Customer Services (stormwater customer services)
Responsible for parcel identification and review, billing and collection of stormwater assessments and related customer information services. The stormwater utility continues to maintain a database that includes all parcels within the stormwater utility area. This information is built upon information purchased from the Sarasota County Property Appraiser’s Office and additional data collected and maintained by the county utility staff. The database contains the necessary information to assure accurate application of the service and capital assessments. Constant monitoring and maintenance of the database is needed to keep pace with development, land use changes, assessment credits and other aspects over time. In order to achieve the monitoring and maintenance needs of the database, a physical inspection is required by ordinance on a large number of parcels.

A short, closed (covered) conduit or pipe that passes stormwater runoff under an embankment, usually a roadway.

The Clean Water Act.

Detention facility or pond
A facility that collects water from developed areas and releases it at a slower rate than it enters the collection system. The excess of inflow over outflow is temporarily stored in a pond or a vault and is typically released over a few hours or a few days.

Direct Discharge
Undetained discharge from a proposed project to major receiving waters.

Drainage Basin (or watershed)
A geographic area, which drains into a major body of water (for example a creek or bayou). The size and shape of a drainage basin is determined by the elevation of the land (topography). There are 27 drainage basins in Sarasota County.

Environmental Protection Agency.

Equivalent Stormwater Unit (ESU)
The Sarasota County Stormwater Environmental Utility currently assesses its customers based on Equivalent Stormwater Units (ESU’s) that are based on the effective impervious area of the average single-family parcel. Based on statistically valid sampling of single family developed parcels, an “ESU Value” of 3,153 square feet was derived from a medium Net Impervious Area (NIA) and NIA of the sampled parcels. The ESU Value is used to establish a basis for comparison of the relative runoff from the base ESU Value and from all parcels within the Stormwater Utility Area, including residential parcels, industrial/commercial parcels and condominiums.

Fiscal Year
The stormwater fiscal year is a period commencing on Oct. 1 of each year and continuing through the next succeeding Sept. 30. (example: Nov. 2013 tax bills are for FY2014, Oct. 1, 2013 to Sept. 30, 2014.)

A temporary rise in flow or stage of any watercourse or stormwater conveyance system that results in stormwater runoff exceeding its normal flow boundaries and inundating adjacent, normally dry areas.

Flood Control
The specific regulations and practices that reduce or prevent the damage caused by stormwater runoff.

Any land area susceptible to inundation by stormwater from any source.

Hydrologic Cycle
The circuit of water movement from the atmosphere to the earth and return to the atmosphere through various stages or processes such as precipitation, interception, runoff, infiltration, percolation, storage, evaporation, and transpiration.

Impervious Surface
A hard surface area which either prevents or retards the entry of water into the soil mantle as under natural conditions prior to development; and/or a hard surface area which causes water to run off the surface in greater quantities or at an increased rate of flow from the flow present under natural conditions prior to development. Common impervious surfaces include roof tops, walkways, patios, driveways, parking lots or storage areas, concrete or asphalt paving, gravel roads, packed earthen materials, and oiled, macadam, or other surfaces which similarly impede the natural infiltration of surface and stormwater runoff. Open, uncovered flow control or water quality treatment facilities are not considered impervious surfaces for determinations of thresholds.

Elevation to the inside bottom of the pipe.

Non-Ad Valorem
An assessment that is not based on the value of the property. Factors such as contribution to the drainage system are used to determine stormwater non-ad valorem assessments; sometimes called a “user-fee”. 

Nonpoint Source (NPS) Pollution
Pollution that, unlike pollution from industrial and sewage treatment plants, comes from many diffuse sources. NPS pollution is caused by rainfall or snowmelt moving over and through the ground. As the runoff moves, it picks up and carries away natural and manmade pollutants, finally depositing them into lakes, rivers, wetlands, coastal waters, and even our underground sources of drinking water. Loadings of pollutants from NPS enter water bodies via sheet flow, rather than through a pipe, ditch or other conveyance.

National Pollutant Discharge Elimination System. The part of the Clean Water Act which requires point source discharges to obtain permits. These permits, referred to as NPDES permits, are administered by the Florida Department of Environmental Protection.

The point where runoff discharges from a sewer pipe, ditch, or other conveyance to a receiving body of water.

Pervious Area
Pervious area is the surface area, which, under standard conditions, is permeable to stormwater runoff and other surface water.

Pervious Area Category
The pervious area category is one or more of the following categories of pervious area: natural state, pasture/meadow, groves and orchards, tilled agriculture, open space and urban pervious.

Pervious Area Factor
The pervious area factor means, for each pervious area category, a number between 0.00 and 1.0 that relates the stormwater burden expected to be generated by such pervious area category to the stormwater burden expected to be generated by an impervious surface. The following pervious area factors have been computed by the county’s consulting engineers and are used to compute the stormwater service assessments:

 Pervious Area Category             Pervious Area Factor
 Natural State  0.000
 Pasture/Meadow  0.002
 Groves and Orchards  0.017
 Tilled Agriculture  0.030
 Open Space  0.037
 Urban Pervious  0.148

Point Source of Pollution

Discrete conveyances, such as pipes or man made ditches that discharge pollutants into waters of the United States. This includes not only discharges from municipal sewage plants and industrial facilities, but also collected storm drainage from larger urban areas, certain animal feedlots and fish farms, some types of ships, tank trucks, offshore oil platforms, and collected runoff from many construction sites.

Retention Ponds
Commonly used facilities that both remove pollutants from stormwater runoff and store floodwaters. A process that halts the downstream progress of stormwater runoff. This is typically accomplished using total containment involving the creation of storage areas that use infiltration devices, such as dry wells, to dispose of stored stormwater via percolation over a specified period of time. (As opposed to a more common detention pond.)

Water originating from rainfall and other precipitation that ultimately flows into drainage facilities, rivers, streams, springs, seeps, ponds, lakes, and wetlands as well as shallow groundwater.

Service Assessments
An assessment levied to fund the stormwater customer service, planning (utility wide operations) and maintenance activities of the utility. The Board of County Commissioners approves the service assessment rates annually during the budget preparation and adoption process. Public hearings are held to obtain input for residents.

  • Customer service activities include the accounting, assessment, collections and database management functions. This assessment is a uniform amount for all parcels in the stormwater utility area.
  • Planning (utility wide operations) activities include basin master planning, engineering services, inspection programs, development plan review, system design, and general management.
    • This assessment, imposed on all parcels in the stormwater utility area, is based on the ESU’s of each parcel (.5 ESU minimum).
  • Maintenance activities include routine ditch and canal clearing, ditch and canal mowing, removal of vegetation from drainage ways, herbicide application to control vegetation growth, cleaning, repair and replacement of storm sewers, and small-scale construction projects.
    • This assessment is based on the ESU’s of each parcel. 

The maintenance assessment is applied only within the utility maintenance area. The utility maintenance area includes the more urbanized areas within the county and the city of Sarasota. Although it includes some county maintained enclaves, the Myakka River basin is also considered a non-maintained basin.

Ordinance No. 94-066 established the Stormwater Environmental Utility Advisory Committee (SEUAC). Comprised of nine residents of the stormwater utility area, SEUAC members are appointed by the Board of County Commissioners. The primary responsibility of the SEUAC is oversight of the utility’s programs, policies and expenditures. The SEUAC makes recommendations to the BCC, based on material and discussions presented at monthly meetings.

Storm Drain
A slotted opening leading to an underground pipe or an open ditch carrying surface runoff. These lead directly to streams and do not go through a treatment or processing plant.

Precipitation from a storm event that flows quickly into streams or accumulates in natural or constructed storage systems. Stormwater often includes pollutants and sediment from land surfaces.

Stormwater Facilities
Systems such as watercourses, constructed channels, storm drains, culverts, and detention/retention facilities that are used for the conveyance and/or storage of stormwater runoff.

Stormwater Level of Service (LOS)
The level of flooding which is considered acceptable for a given rain event. Sarasota County’s established level of service prohibits structure flooding and flooding of evacuation routes in a 100-year (1 percent chance) storm event. Flooding of neighborhood streets to a depth of 12 inches at the curb is allowed in a 100-year storm event.

Stormwater Management
Functions associated with planning, designing, constructing, maintaining, financing and regulating the facilities (both constructed and natural) that collect, store, control and/or convey stormwater. Stormwater System The entire assemblage of stormwater facilities located within a watershed.

Stormwater Utility Area
The unincorporated area of Sarasota County and the incorporated area in the city of Sarasota.

Surface Water
Water that remains on the surface of the ground, including rivers, lakes, reservoirs, streams, wetlands, impoundments, seas, estuaries, etc.

A shallow drainage conveyance with relatively gentle side slopes, generally with flow depths less than one foot. Often lined with grass and used as a conveyance for stormwater.

Total Maximum Daily Load (TMDL)
The maximum amount of pollutants which can released into a water body without adversely affecting the water quality.

Urban Runoff
Stormwater from urban areas, which tends to contain heavy concentrations of pollutants from urban activities.

A geographic area in which water, sediments, and dissolved materials drain to a common outlet, typically a point on a larger stream, a lake, an underlying aquifer, an estuary, or an ocean. A watershed is also sometimes referred to as the "drainage basin" of the receiving water body.

An area inundated or saturated by ground or surface 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.