Glossary

# - A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z

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  • 0.2% (500-year) Floodplain

    The area of land that has a 0.2% chance of being inundated by flood waters from a bayou, stream or creek in a given year. It is commonly referred to as the 500-year floodplain. This is a regulatory standard used to administer floodplain management programs and the National Flood Insurance Program (NFIP). Statistically, the 0.2% (500-year) flood has a 6% chance of occurring during a 30-year period of time – the length of many mortgages.

    The 0.2% (500-year) floodplain is referred to as Zone X for insurance purposes on Flood Insurance Rate Maps (FIRMs).

  • 0.2% (500-year) Rainfall

    An amount of rain having a 0.2% chance of being equaled or exceeded in any given year. For Harris County, this amount of rainfall is just less than 19 inches in 24 hours.

  • 1% (100-year) Floodplain

    The area of land that has a 1% chance of being inundated by flood waters from a bayou, stream or creek in a given year. It is commonly referred to as the 100-year floodplain. This is a regulatory standard used to administer floodplain management programs, the National Flood Insurance Program (NFIP) and to set building requirements for new construction. Statistically, the 1% (100-year) flood has a 26% chance of occurring during a 30-year period of time – the length of many mortgages.

    The 1% (100-year) floodplain is the Base Flood or Special Flood Hazard Area. It is referred to as Zones AE, AO, A, or VE for insurance purposes on Flood Insurance Rate Maps (FIRMs). Properties located in these mapped zones are required to have flood insurance if the owner has a federally backed mortgage on the property.

  • 1% (100-year) Rainfall

    An amount of rain having a 1% chance of being equaled or exceeded in any given year. For Harris County this amount of rainfall is just over 13 inches in 24 hours or just under 11 inches in 12 hours.

  • 10-Foot Contour

    A contour line is a line on a map that joins points of equal elevation. Each 10-foot contour line will increase or decrease in increments of 10 feet to illustrate the identified land elevation.

  • 2-Foot Contour

    A contour line is a line on a map that joins points of equal elevation. Each 2-foot contour line will increase or decrease in increments of 2 feet to illustrate the identified land elevation.

A

  • Acre-Feet

    Used to express volume of storage usually in a detention basin. One Acre-Foot is equal to one acre times a one-foot depth or 43,560 cubic feet (325,850 gallons).

  • Alternatives

    Combinations of one or more components that provide a complete plan to reduce flood damages. A number of alternatives may be formulated, and the preferred one is deemed the "recommended alternative."

  • Appraisal

    A written estimate of the value of an asset or property prepared by a qualified, independent party.

B

  • Base Flood

    A flood having a 1 % chance of being equaled or exceeded in any given year. This flood is sometimes called the 1% or 100-year flood.

  • Base Flood Elevation

    This is the elevation above the average sea level that waters from a 1% (100-year) flood will reach at a given point along a creek or bayou. These elevations are determined using hydrology and hydraulic computer models. The elevations are then mapped on the topographic data for the county to produce the 1% (100-year) floodplain.

  • Benefit-to-Cost Ratio

    Represents the overall efficiency of a plan. Determined by dividing the value of the annual benefit by the annual cost.

  • BMP

    Best Management Practices

  • Bridge Modification

    The replacement, extension or reinforcement of a bridge in order to remove an impediment to flow or accommodate a channel enlargement.

  • Buyout

    The elimination of potential flood damages to houses or other types of structures by acquiring them and removing them.

  • Bypass Channel

    The construction of a new channel in order to convey stormwater runoff around an area. Usually required due to right-of-way considerations or to avoid environmentally sensitive areas.

C

  • Capacity

    The measure of water capable of flowing through a channel, measured in cubic feet per second (CFS). Also the measure of how much water a stormwater detention facility holds, usually measured in acre-feet (AC-FT).

  • Capital Improvement Program

    The District's CIP shows the schedule and projected funding for flood damage reduction projects for current and future years. The Harris County Flood Control District's CIP is presented for a five-year time frame and adjusted annually.

  • Cellular Concrete Mats

    A mat consisting of interlocking concrete "jigsaw puzzle-looking" blocks that is sometimes placed as a lining on the sides and bottom of a channel. These mats increase the efficiency of the flow of stormwater in the channel. Because the blocks have openings through them, grass and other vegetation can grow through them minimizing the occurrence of erosion in an aesthetically pleasing manner.

  • Channel

    A course or passage through which stormwater may move or be directed. It is a generic term used by the Harris County Flood Control District in reference to ditches, bayous, creeks or other smaller tributaries. A channel can vary in shape and size, and can be either natural or man-made.

  • Channel Flow

    The amount of stormwater flowing through a channel, often measured in cubic feet (of stormwater) per second (or CFS).

  • Channel Modification

    A man-made change to a channel's characteristics, typically for the purposes of reducing flood damages by increasing its overall conveyance. This can be accomplished by widening and/or deepening the channel, reducing the friction by removing woody vegetation or by lining the channel with various materials.

  • Citizens Advisory Committee

    A group of stakeholders that meet regularly to discuss ideas and gain consensus on items of importance relative to Harris County Flood Control District activities, such as a study, design, construction project or maintenance practice.

  • CLOMR

    A Conditional Letter of Map Revision (CLOMR) is FEMA's comment on a proposed project that would affect the hydrologic and/or hydraulic characteristics of a flooding source and thus result in the modification of the existing regulatory floodway or effective Base Flood Elevations. There is no appeal period. The letter becomes effective on the date sent. This letter does not revise an effective National Flood Insurance Program map, it indicates whether a proposed project would produce a change in a Special Flood Hazard Area by FEMA if later submitted as a request for a Letter of Map Revision.

  • Closing

    The final phase of a transaction, especially the meeting at which procedures are carried out in the execution of a contract for the sale of real estate.

  • Closing Costs

    Fees a home buyer or seller pays at closing, such as property insurance, taxes, attorneys’ fees, an origination fee, an amount placed in escrow, title insurance, mortgage insurance premium, points and filing fees associated with the sale of property.

  • Compartment

    A section of a detention basin designed so that the excavation can be constructed separately, and potentially operated separately, from other sections of the same detention basin.

  • Components

    Specific applications of flood damage reduction "tools," such as a detention basin or channel enlargement, at a particular location.

  • Condemnation

    The legal process for the taking of private property.

  • Confluence

    The intersection of two or more streams, or where one flows into another.

  • Conveyance

    The ability of a channel or other drainage element to move stormwater.

  • Corps

    U.S. Army Corps of Engineers, also USACE. The federal agency authorized to partner with local governments (such as the District) to conduct major water resources projects. The Corps operates nationally and evaluates funding requirement for all projects. The Corps also supports U.S. military operations. The Corps office for this region is located in Galveston, Texas. For more info on this region's Corps, go to the U.S. Army Corps of Engineers, Galveston District's website at www.swg.usace.army.mil. For more general info on the Corps, go to www.usace.army.mil/.

D

  • D/S

    Downstream

  • Data Collection Form

    This is the form used by the Harris County Flood Control District to compile information from a homeowner who wishes to participate in the home buyout program. It is sometimes called a "Voluntary Acquisition Form."

  • Deed

    A legal document that evidences a person’s ownership of and right to possess a property.

  • Desired Capacity

    A measure of what area communities, in conjunction with the Harris County Flood Control District, determine is needed for a project to provide an acceptable level of flood damage reduction. This desired capacity is based on factors such as the extent of flooding, available land and available funding, sometimes through partnerships. See Capacity.

  • Detention Basin

    An area of land, usually adjacent to a channel, that is designed to receive and hold above-normal stormwater volumes. Most stormwater detention basins in Harris County are excavated. The detained stormwater then slowly drains over time out of the detention basin as the flow in the channel and associated water surface elevations recede. (also Stormwater Detention)

  • Disaster Area

    When a disaster is beyond the capabilities of state and local government to respond, the Governor must make a formal request to the President to declare the affected region a "disaster area." When the presidential declaration is enacted, federal assistance is made available to public and certain non-profit entities, as well as to individuals who were adversely affected by the disaster. The assistance is available in many forms, including monetary, temporary housing, crisis counseling and even legal assistance. For more on the Disaster Declaration process, go to: www.fema.gov/rebuild/recover/dec_guide.shtm.

  • Discrete Segment

    Unique term developed to describe the logical pieces of large, long range projects for determining Federal reimbursement to the local sponsor. Once a discrete segment of a project (e.g. defined element of channel or stormwater detention construction) is complete and functional, it qualifies for reimbursement.

  • Duplication of Benefits

    A situation in which benefits are derived from two federal government-sponsored programs for the same item. An example would be a homeowner collecting flood insurance to cover damage to the home, and then being paid full pre-flood value for the home without deducting the insurance proceeds. Harris County Flood Control District policy and FEMA regulations prohibit duplication of benefits in a home buyout.

E

  • Easement

    A limited interest in real property for a specific purpose, usually designated in the granting instrument or plat. Another entity or individual has fee title to the property.

  • Element

    A major subdivision of an overall flood damage reduction plan, divided based on scheduling, financial or geographic criteria.

  • Elevation

    The vertical distance measured from a datum to a specific point of interest. Ground elevations in Harris County range from sea level in the southeast (by Galveston Bay) to over 300 feet above sea level in the Northwest corner of the county. Base Flood Elevations are an example of elevations above a certain datum, and when combined with ground elevations, produce the mapping of a floodplain.

  • Elevation Certificate

    An Elevation Certificate is a detailed survey of a structure's elevation to see if it is above or below the base flood elevation. An Elevation Certificate can be used to reduce the cost of flood insurance or even remove a particular structure from the 1% (100-year) floodplain.

  • Encroachment

    Construction, such as a wall, fence, building, etc., on the property of another.

  • EPA

    Environmental Protection Agency

  • Escrow

    An account established by a lender in which a homebuyer’s funds are deposited for the payment of items such as property taxes and homeowner’s insurance.

  • Existing Capacity

    The measure of how much water a channel can currently carry, measured in cubic feet (of storm water) per second (CFS). Also the measure of how much water a stormwater detention facility can currently hold, usually measured in acre-feet (AC-FT) of volume.

F

  • Fair Market Value

    "The most probable price which a property should bring in a competitive and open market under all conditions requisite to a fair sale, the buyer and seller each acting prudently and knowledgeably, and assuming the price is not affected by undue stimulus..." The value for District transactions is determined by an appraiser, licensed or certified by the State of Texas.

  • Fee Simple

    Full ownership of real property by an individual or entity.

  • FEMA

    (Federal Emergency Management Agency) - The federal agency responsible for providing leadership and support to reduce loss of life and property and to protect our institutions from all types of hazards. This is accomplished through a comprehensive, risk based, all hazards emergency management program consisting of mitigation, preparedness, response, and recovery. In relation to flooding hazards, FEMA is the federal agency responsible for administering the National Flood Insurance Program (NFIP).

  • FIRM Panel

    FIRM stands for Flood Insurance Rate Map. In order to print the FEMA Flood Insurance Rate Maps at a scale of 1-inch = 1,000-feet, the maps are broken out into over 150 FIRM panels that cover the entire Harris County area.

  • Flap Gate

    A flap gate is a simple mechanical device used to control the direction of flow of stormwater and is typically used at the end of a pipe draining into a channel. The flap gate allows water to drain from the pipe into the channel but closes when stormwater in the channel begins to rise higher than the water being delivered by the pipe.

  • Flood Bench

    Typically, a design feature obtained by enlarging a channel's cross-sectional geometry so that it varies in width and steepness, creating flatter slopes and even plateaus, giving completed segments more of a natural appearance.

  • Flood Control District

    Harris County Flood Control District

  • Flood Insurance Rate Maps

    Prepared by FEMA, Flood Insurance Rate Maps, or FIRMs, show areas that have the highest probability of flooding and illustrate the extent of flood hazards in a flood-prone community. These maps are used to determine flood insurance rates for communities participating in the National Flood Insurance Program (NFIP).

    Properties located in mapped zones AE, AO, A, or VE are required to have flood insurance if the owner has a federally backed mortgage on the property.

  • Flood Insurance Study

    A study FEMA initiates to undertake a new hydraulic and/or hydrologic analysis for streams within a community. Often, these studies incorporate the new information into the FEMA Flood Insurance Rate Maps (FIRMs).

  • Floodplain

    From time to time, bayous and creeks naturally come out of their banks due to heavy rainfall and inundate the adjacent land. This area that is inundated is referred to as a floodplain. Residences and businesses within the floodplain are considered to be at risk of being damaged by flooding. The floodplain is typically expressed by stating its frequency of occurrence. For example, the 1% (100-year) floodplain represents an area of inundation having a 1% chance of being equaled or exceeded in any given year, whereas the 2% (50-year) flood plain has a 2% chance of being equaled or exceeded in any given year. FEMA Flood Insurance Rate Maps (FIRMs) show the 1% (100-year) and 0.2% (500-year) floodplains.

  • Floodplain Administrator

    Sometimes called a local floodplain manager, the Floodplain Administrator is the person identified within a local governmental jurisdiction to administer their community’s floodplain management and development regulations in accordance with the National Flood Insurance Program (NFIP). The Floodplain Administrator keeps the official FEMA Flood Insurance Rate Maps (FIRMs) that document flood hazard zones in their community. The Harris County Flood Control District is not a floodplain administrator.

  • Floodplain Management

    In order for a community to participate in the National Flood Insurance Program (NFIP), the community is required to enforce regulations on land development projects to avoid increasing flood levels or flood hazards and to avoid creating new flood hazards. This work is performed by the local Administrator. Most of the 35 communities in Harris County, including the City of Houston and Unincorporated Harris County, have regulations or ordinances that exceed the NFIP minimum standards.

  • Floodway

    For most waterways, the floodway is where the water is likely to be deepest and fastest. It is the area of the floodplain that should be reserved (kept free of obstructions) to allow floodwaters to move downstream. Technically,the floodway is typically calculated by finding the area that must be reserved to carry and discharge the 1% (100-year) flood without increasing the base flood by more than 1-foot.

  • Flowline

    A line formed representing the lowest point in the bottom of and along a specified length of a channel.

  • Fluvial Geomorphology

    The study of river behavior and river-related landforms, such as riverbeds, floodplains and stream forms.

  • FY

    Fiscal year

G

  • Gabion

    Rock-filled wire baskets either laid as mattresses or stacked in a manner that forms a retaining wall. Gabions are sometimes used to support the banks and sides of channels for structural reasons, as well as minimize the occurrence of erosion.

  • GIS

    (Geographic Information System) - A computer program or programs used to store a wide variety of types of information and link that information to a specific geographic location. Some examples of this information the District utilizes would be streets, bayous and channels, HCAD parcel data, contours, floodplains and all the data that supports this information such as names, location and much more.

  • GPS

    (Global Positioning System) - GPS is a system that uses satellites to accurately determine the location of any point on earth, and it helps to create the most accurate floodplain maps possible

  • Greens Bayou Wetlands Mitigation Bank

    A 1,800-acre area of thriving man-made wetlands being created by the Harris County Flood Control District and located at the confluence of Greens Bayou and Garners Bayou in Northeast Harris County. Mitigation banking provides developers, utility providers and government entities with the opportunity to pay a one-time fee to purchase "credits" (or already-established areas) within the wetlands bank to satisfy statutory wetland mitigation requirements, thus offering a more comprehensive, effective and long-lasting solution.

  • GRR

    General Re-evaluation Report. Submitted to USACE for approval of a revised plan for all or part of a project.

H

  • Harris County Flood Control District

    HCFCD, (the District)
    A special purpose district created by the State Legislature in 1937 in response to devastating floods which struck the region in 1929 and 1935. The District's boundaries are coincident with Harris County, and the Harris County Commissioners Court serves as the District's "board of directors" to provide elected representation. The District is responsible for devising flood damage reduction plans, implementing the plans, and maintaining the primary drainage infrastructure.

  • Hydraulics

    The study of moving fluid. In the case of the District's work, hydraulics refers to analyzing the movement of stormwater flows in channels, pipes and detention basins to determine certain properties like stormwater depths and stormwater velocities.

  • Hydrology

    The study of the rainfall-stormwater runoff process. Hydrological procedures are used to estimate the expected amount of stormwater entering a drainage system from a certain amount of rain falling over a certain watershed area.

I

  • Impacts

    The expected change in stormwater characteristics (i.e. stormwater flow), velocities and depths caused by proposed changes in the watershed.

  • Infrastructure

    The land, buildings and other assorted structures that serve public use. For the Harris County Flood Control District, infrastructure typically refers to the primary drainage system, including channels and detention basins (not streets, storm sewers, and roadside ditches).

  • Insufficient Capacity

    Exists when the desired capacity of a channel or stormwater detention facility exceeds the existing capacity; that is, when a channel or a detention facility cannot carry or hold all of the stormwater that could flow to it.

J

  • JTF

    Joint Task Force - Cooperative partnership between the Harris County Flood Control District, the City of Houston, Harris County, and the Texas Department of Transportation to address Phase I stormwater permit requirements.

K

L

  • Levee

    A physical barrier constructed to protect areas from rising floodwaters.

  • LiDAR

    (Light Detection and Ranging) - LiDAR is a commercial technology that uses a laser mounted in an airplane to measure the elevation of the ground.

  • Lien

    A legal claim allowed to a creditor against a debtor’s property that must be paid when the property is sold. A legal claim allowed to a creditor against a debtor's property that must be paid when the property is sold in order to transfer.

  • LOMR

    (Letter of Map Revision) - FEMA's modification to an effective Flood Insurance Rate Map (FIRM), or Flood Boundary and Floodway Map (FBFM), or both. LOMRs are generally based on the implementation of physical measures that affect the hydrologic or hydraulic characteristics of a flooding source and thus result in the modification of the existing regulatory floodway, the effectiveBase Flood Elevations (BFEs), or the Special Flood Hazard Area (SFHA). The LOMR officially revises the Flood Insurance Rate Map (FIRM) or Flood Boundary and Floodway Map (FBFM), and sometimes the Flood Insurance Study (FIS) report, and when appropriate, includes a description of the modifications. The LOMR is generally accompanied by an annotated copy of the affected portions of the FIRM, FBFM, or FIS report. An Appeal/Protest period exists only when there is a change in the BFE.

M

  • Mitigation

    To offset the impact of one action by implementing another. Examples of various forms of mitigation, as used by the Harris County Flood Control District, include:

    1. Offsetting the impacts from land development projects. This is usually in the form of a stormwater detention basin. The development area will drain into the stormwater detention basin, and ultimately, into a channel.
    2. Offsetting the impacts of wetlands/habitat losses. State and Federal laws protect certain wetlands and habitat. Through a permit process, agencies require projects to "avoid, minimize and mitigate" any unavoidable losses. Mitigation is typically done through recreation of the affected wetlands or habitat areas. Certain wetlands losses can be mitigated with the District's wetlands mitigation banking.
    3. Offsetting dollar losses from previous or expected flood damages. This can come in the form of buyout or even elevating a structure or dwelling. The Harris County Flood Control District may partner with FEMA or the U.S. Army Corps of Engineers in various buyout endeavors to eliminate the possibility of a structure flooding by purchasing it and demolishing it, thus removing it forever from a flood-prone area. A structure that no longer exists can no longer incur flood damages.

    An individual homeowner can also mitigate financial losses caused by flood damage by purchasing a flood insurance policy.

  • Mortgage

    A legal document that pledges a property to a lender as security for the payment of a loan or debt.

  • Moving Costs

    Expenditures associated with moving, including packing and unpacking, temporary storage of personal property, transportation, moving insurance, disconnecting and reconnecting household appliances and other related items.

  • Moving Expenses

    The direct costs associated with moving the personal property of qualified homeowners from a flooded home that was purchased by the District. (Note that this does not apply for the voluntary buyout program.)

  • MS4

    Municipal Separate Storm Sewer Permit

  • Multi-use

    The ability to provide more than one use. This usually is in reference to drainage facilities or detention basins that not only provide for flood damage reduction, but can also accommodate other uses, such as hike-and-bike trails, sports fields, wildlife habitat, etc.

N

  • NFIP

    (National Flood Insurance Program) - Created by Congress in 1968 to provide low cost flood insurance for property owners in flood-prone communities. In exchange for flood insurance eligibility, communities agree to implement and enforce floodplain management measures to reduce the possibilities of future damage. FEMA arranges for periodic community assistance visits with local officials to provide technical assistance regarding complying with NFIP floodplain management requirements. FEMA works with local officials to evaluate the FIRMs and associated Flood Insurance Study and conducts updates as needs and priorities dictate. Harris County and the incorporated cities within the county are participants in the NFIP, so flood insurance is available to all residents.

  • NOAA

    National Oceanic and Atmospheric Administration

  • Non-Point Sources

    Indirect sources of stormwater runoff - such as roadways, yards or agricultural areas - that can be the origins of stormwater pollution in the overall drainage infrastructure.

  • NPDES

    (National Pollutant Discharge Elimination System) - As authorized in 1990 by the Clean Water Act, NPDES is a federally mandated permit program intended to control water pollution by regulating point sources that discharge pollutants into waters of the United States. Under the storm water component of the permit program, the federal government requires municipal separate storm sewer systems (MS4s) serving a population of 100,000 or more to have a stormwater NPDES permit.

O

  • O&M

    Operation and Maintenance

  • Other Frequency Floods

    There are an infinite number of frequency floods that can occur. The 1% (100-year) flood is used by many as a standard for regulations, designs and National Flood Insurance Program purposes. Other floods often used consist of the 0.2% (500-year) flood, the 2% (50-year) flood, the 10% (10- year) flood and the 50% (2-year) flood.

  • Outfall

    An outfall is simply the pipe, channel, or opening where water "falls out" and then into another body of water, typically a drainage channel. In a typical stormwater detention basin, the outfall is at or connected to the lowest point of the basin so that detained water drains completely.

  • Out-of-Bank

    The condition in which the water level of a channel rises above the top of its banks and spills into the surrounding land area.

  • Oxbow

    Generally, a U-shaped bend or meander in a channel. Oxbows are sometimes "cut off" and abandoned when a channel is straightened. This can occur both naturally or by man-made means.

P

  • Pay-As-You-Go

    Pay-As-You-Go refers to using current income (cash) instead of relying on debt (e.g. bonds) as a way to fund projects. Cash funding avoids long-term debt and its associated interest payments.

  • Peak Flow

    (or Channel Peak Flow) - The maximum flow of stormwater flowing through a channel at a given location, based on a certain amount of rainfall falling in that area.

  • Physical Condition

    A detailed listing of all of the physical aspects of a channel that can influence its effectiveness. Physical condition includes the bottom and sides of a channel, as well as the condition of structures, such as bridges.

  • Point Sources

    Specific conveyances, such as pipes or man-made ditches that flow into, or are part of the overall drainage infrastructure.

  • Ponding

    The process, occurring after a rainfall, when water gathers in low lying areas throughout a watershed. Frequently referring to water standing in the streets when the capacity of the storm sewer is exceeded.

  • Pre-Flood Fair Market Value

    "The most probable price which a property should bring in a competitive and open market under all conditions requisite to a fair sale, the buyer and seller each acting prudently and knowledgeably, and assuming the price is not affected by undue stimulus." The value for District transactions is determined by an appraiser, licensed or certified by the State of Texas. "Pre-flood" is a term relating to the buyout program which establishes the value prior to recent flood damages.

  • Project Process

    Project Process includes the Feasibility Stage, Development Stage, Property Acquisition and Utility Relocation Stage, Design Stage and Construction Stage. A funding allotment must be secured for each stage of the project process.

Q

R

  • Relocation Assistance

    Financial assistance and real estate guidance provided to the qualified owner of a primary residence to relocate and purchase a comparable, safe, and sanitary home.

  • Repetitive Loss Property

    Homes that have received more than $1,000 of flood insured damage two or more times in the last ten years will appear on the National Flood Insurance Program (NFIP) repetitive loss database and receive higher priority for certain types of buyout.

  • Residences

    Any dwellings in which people live, including single-family houses, apartment units, mobile homes and travel trailers

  • Right of Way

    (also right-of-way, ROW)
    An interest in real property, either in fee or easement.

  • Right-of-Way

    Land used by a public agency for public purposes, such as building roads or improving channels.

  • Riparian

    (Corridor or Zone) - The area of land along and adjacent to a waterway (river, bayou, creek, stream, etc.). Trees, plants and grasses along these waterways are called riparian vegetation. A riparian zone from an ecological perspective may occur in many forms including grassland, woodland, wetland or even non-vegetative. Riparian zones may be natural or engineered for soil stabilization or restoration. In some regions the terms riparian woodland, riparian forest, riparian buffer, or riparian corridor are used to characterize a riparian zone.

  • Riprap

    Rocks or broken pieces of concrete often placed in areas where the flow of stormwater is expected to cause erosion. The riprap serves as "armor" for areas of channels and detention basins to minimize the occurrence of erosion.

  • Riverine Flooding

    Flooding that is the result of creeks and bayous leaving their banks as a result of a heavy rainfall. This type of flooding is mapped on the Flood Insurance Rate Maps.

  • Runoff

    The stormwater from rainfall not absorbed by the ground that flows in to the local drainage system, and ultimately, streams and bayous.

S

  • Section 211

    [or Section 211 (f)] - A Section 211 project refers to the Water Resources Development Act of 1996 (WRDA 1996). Section 211 gives authority to authorized non-federal agencies, such as the Harris County Flood Control District, to take the lead on planning studies and construction of major flood damage reduction projects. The District will be eligible for the same amount of federal dollars but will manage the projects with a higher degree of local control. The study process, requirements to achieve project approval and funding for construction are the same as those for the U.S. Army Corps of Engineers. Reimbursement for the federal share of cost is possible after approved projects are completed.

  • SFHA

    (Special Flood Hazard Area) - An area defined on a FEMA Flood Insurance Rate Map with an associated risk of flooding.

  • Sheet Flow

    (Overland Flow Flooding) - Flooding that occurs when intense local rainfall flows overland to reach a channel. Frequently, this conditions exists when runoff exceeds storm sewer or roadside ditch capacity, and the water can "pond" in the streets deep enough to flood residences that are not even near a creek of bayou. The water will seek a path to the channel by flowing overland (Sheet Flow). When residences and other structures are in that path, flooding occurs and this type of flooding is not identified on the Flood Insurance Rate Maps. This is also known as the "Fifth Scenario" when discussing Harris County's four types of Floodplains

  • Stormwater Detention Basins

    An area of land, usually adjacent to a channel, that is designed to receive and hold above-normal stormwater volumes. Most stormwater detention basins in Harris County are excavated. The detained stormwater then slowly drains, over time, out of the detention basin as the flow in the channel and associated water surface elevations recede.

  • Subsidence

    In this region, subsidence - or the sinking of the land surface - has been caused primarily by the pumping of ground water. Beneath Harris County are a series of sand and clay beds that provide water (aquifers). As water is withdrawn from the aquifers, pressure decreases and the clay particles begin to compress. The ultimate effect of these layers compacting is subsidence.

  • Substantially Damaged Property

    Flood damage to a structure where the cost to repair equals or exceeds 50% of the value of the structure, excluding the land value.

  • Subwatershed

    (also Tributary watershed) - The land area that drains to one of the smaller streams that flow to the main channel of a watershed (i.e. Halls Bayou subwatershed is within the Greens Bayou watershed).

  • SWMP

    Stormwater Management Program

  • SWPPP

    Storm Water Pollution Prevention Plan

T

  • Topographic Data

    Detailed information about the shape of the earth including ground elevations and ground contours.

  • TPDES

    The state program for issuing, amending, terminating, monitoring, and enforcing permits, and imposing and enforcing pretreatment requirements, under the Clean Water Act §§ 307, 402, 318 and 405, Texas Water Code, and Texas Administrative Code regulations.

  • TPWD

    Texas Parks and Wildlife Department

  • Tributary

    A channel through which water may move or be directed that ultimately flows into a larger channel, usually bayous and creeks in Harris County.

  • Tributary Watershed

    (also Subwatershed) - The land area that drains to one of the smaller streams that flow to the main channel of a watershed (i.e. Halls Bayou is a subwatershed of Greens Bayou watershed).

  • TSARP

    Tropical Storm Allison Recovery Project - The Tropical Storm Allison Recovery Project was a joint-effort project between FEMA and the Harris County Flood Control District to gather information about Tropical Storm Allison and to create new flood hazard information for all of Harris County. It resulted in the citizens of Harris County having more information about flooding and being better prepared for the next flood.

  • TxDOT

    Texas Department of Transportation

U

  • U/S

    Upstream

  • Unincorporated Harris County

    The area in Harris County, Texas, which is not within an incorporated area of a city, town, village, or within the jurisdiction of the Port of Houston Authority.

  • USACE

    (United States Army Corps of Engineers) - The federal agency authorized to partner with local governments (such as the District) to conduct major water resources projects. The Corps operates nationally and evaluates funding requirements for all projects. The Corps also supports U.S. military operations. The Corps office for this region is located in Galveston, Texas.

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  • Wastewater Treatment Facility

    An arrangement of devices and structures, excluding septic tanks, constructed and installed for the purpose of treatment of wastewater from domestic, commercial or industrial sources or combinations thereof, and which discharge its treated effluent into any surface water.

  • Water Surface Elevation

    The distance the water surface in a creek or bayou is above mean sea level, measured at a given location along a creek or bayou.

  • Water Surface Elevation Profile

    Shows the elevation above mean sea level of the 1% (100-year) or 0.2% (500-year) floodplain along all the studied stream miles in a particular watershed.

  • Watershed

    A geographical region of land or "drainage area" that drains to a common channel or outlet, mostly creeks and bayous in Harris County. Drainage of the land can occur directly into a bayou or creek, or through a series of systems that may include storm sewers, roadside ditches, and/or tributary channels.

  • Weir

    A structure typically constructed to control the timing and amount of stormwater flowing into an adjacent detention basin. As the stormwater level in the channel increases, water flows into the basin over the weir. The lower a weir, the sooner the rising stormwater enters the basin. The longer a weir, the greater the flow of stormwater entering the basin.

  • Working Day

    A calendar day, not including Saturdays, Sundays and County holidays, in which weather or other conditions not under the control of the Contractor allow performance of work on a project for a continuous period of not less than 7 hours between 7:00 a.m. and 6:00 p.m. The contractor cannot perform any work on non-work days without the District's approval.

  • WRDA

    Water Resources Development Act of 1996 (WRDA 1996) - A Section 211 project refers to the Water Resources Development Act of 1996 (WRDA 1996). Section 211 gives authority to authorized non-federal agencies, such as the Harris County Flood Control District, to take the lead on planning studies and construction of major flood damage reduction projects. The District will be eligible for the same amount of federal dollars but will manage the projects with a higher degree of local control. The study process, requirements to achieve project approval and funding for construction are the same as those for the U.S. Army Corps of Engineers. Reimbursement for the federal share of cost is possible after approved projects are completed.

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