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WEB-BASED HANDBOOK (Legacy Edition). CLICK HERE to submit comments.
Because of staff changes and Randolph Langenbach's retirement from FEMA, these handbooks were never published on the FEMA website.  These are the only copies available.


 

APPENDIX B 

 

GLOSSARY

&

INDEX OF FLOOD DAMAGE KEYWORDS

[Keywords are underlined]

Armoring. Placing materials, such as riprap, to protect an embankment or a stream bank.

Backwater. The rise in a stream's water surface elevation caused by an obstruction or constriction to the flow, such as by a dam, bridge, culvert, or a temporary obstruction.

Bank. The lateral boundaries of a stream confining all flow levels that do not rise above them and flow out onto the floodplain. The bank on the left side of a channel looking downstream is the left bank.

Bank protection. Rock, concrete, asphalt, vegetation, or other armor protecting a bank of a stream from erosion. Includes devices used to deflect the forces of erosion away from the bank. See Embankment Slope Protection.

Barbs. See Flow diverters.

Base flood elevation. See Design flood elevation.

Batters. Steel plates attached to the upstream faces of bridge piers to protect them from damage due to the impact of floating debris. pp. 66 and 67.

Berms. Earth-filled structures placed on a floodplain to divert flood flows, most commonly into bridge or culvert openings. The earth fill should be erosion-resistant and the berms should be covered with erosion-resistant vegetation. Berms should be located to ensure no significant increase in water surface elevations. pp. 43 and 75.

Bevel ring, Entrance. A round collar placed on a culvert entrance to divert the flow into the culvert. The collar is beveled from its outer surface inward to the culvert entrance.

Bio-engineering. Use of plant materials to stabilize hill slopes or stream banks. It often involves fascine and bundles in conjunction with other 'hard' structures such as logs, root wads, rock toes, or wooden crib structures.

Bio-filtration. The aerobic and anaerobic processes used to break down wastes, as is typically implemented at a waste water or sewage treatment plant.

Bucket outlet. A concrete or rock structure placed at a culvert outlet to dissipate the energy of the flow as it exits the culvert. The structure is curved upward to throw the water jet downstream.

Capacity. The effective carrying ability of a drainage structure.

Catch basin. A structure that collects water.

Check dams. A small rock or concrete structure generally placed laterally across steep ditches for the purpose of reducing the velocity in the ditch. pp. 4 and 7.

Critical facility. Critical facilities provide essential services to a community, like a fire station, hospital, or nursing home. When relocated or reconstructed, the critical facility must not be located within the 500-year floodplain. The distinction of these facilities is that even a small flood can have life-threatening risks, such as due to access and/or operations issues. See also 44 CFR Chapter 9.4 for a list of critical actions.

Culvert. A closed conduit, other than a bridge, which allows water to pass through a roadway prism.

Culvert, Additional. Intended to mitigate culvert misalignment. Additional culverts are designed to stand alone. Individual design capacities are determined based on the amount of anticipated flow through separate stream channels that have migrated (or are expected to migrate) away from the main stream. pp. 6 and 41.

Culvert entrance bottoms, Paving. pp. 22, 25, and 35-36.

Culvert entrance, Rounding. pp. 22, 25, and 37.

Culvert entrance, Shape. pp. 35 and 36.

Culverts, Multiple. Intended to mitigate insufficient capacity. Multiple culverts are designed as part of the main stream culvert system. They are located at the main stream culvert site and should be at different elevations in the embankment. (i.e., Separated by 0.1 times the diameter of the culvert.)

Cutoff wall. A wall at the end of a drainage structure, the top of which is an integral part of the drainage structure. This wall is usually buried and its function is to prevent undermining of the drainage structure if the natural material at the outlet of the structure is eroded by the water discharging from the end of the structure. Cutoff walls are sometimes used at the upstream end of a structure when there is a possibility of erosion. pp. 35 and 36

Debris barrier (trash rack). A deflector placed at the entrance of a culvert upstream, which tends to deflect heavy floating debris or boulders away from the culvert entrance during high velocity flow. pp. 21-23, 30, 35-37, 39, 41-45, and 68.

Debris basin. Any area upstream from a drainage structure utilized for the purpose of retaining debris in order to prevent clogging of drainage structures downstream.

Debris crib. Open crib-type structure placed vertically over the culvert inlet in log-cabin fashion to prevent inflow of coarse bedload and light floating debris.

Debris deflector. Structure placed at the culvert inlet to deflect the major portion of the debris away from the culvert entrance. They are normally "V" shaped in plane with the apex upstream. pp. 30, 49-52, 56-58, 61, 65, and 67.

Debris fins. Walls built in the stream channel upstream of the culvert. Their purpose is to align debris, such as logs, with the axis of the culvert so that the debris will pass through the culvert barrel without clogging the inlet. They are sometimes used on the bridge piers to deflect drift. pp. 30, 66, and 67.

Design flood elevation. Unless the community has designated a higher elevation, the 100-year floodplain for bridges, buildings and other important facilities, the 500-year floodplain for critical facilities, and the maximum flood that frequently occurs for all other facilities.

Detention storage. Surface water moving over the land is in detention storage. Surface water allowed to temporarily accumulate in ponds, basins, reservoirs, or other types of holding facility, and which is ultimately returned to a watercourse or other drainage system as runoff is in detention storage.

Drawdown. A lowering of the surface water elevation of a stream as it approaches and flows through a bridge or culvert. It is a measure of the difference of the water surface elevation upstream from the bridge or culvert and a short distance downstream from their enrances.

Eddies. Currents of water moving in circular (whirlpool) patterns contrary to the main direction of flood flows. The eddies may move laterally to the downstream direction of flow or at various angles upstream and downstream.

Elevate. pp. 54, 55, 73, 74, 83, and 95.

Embankment slope protection. pp. 4, 9, 15, 21-24, 30, 32, 35-37, 39, 41-45, 49-52, and 56-58.

Emergency spillway. A constructed channel at a dam or other structure designed to pass flood flows that exceed the design capacity of the flow through structures.

Endnoses. Triangular or curved structures added to the upstream side of piers to deflect floating debris and high stream velocities. pp. 63, 66, and 67.

Endwall (treatment/design). A wall at the end of a drainage structure designed to prevent erosion of the embankment at its entrance or outlet. pp. 21, 22, 35-37, and 41-45.

Energy dissipater. A rock or concrete structure designed to reduce the velocity of the flow exiting a culvert to prevent erosion of the streambed and banks. pp. 10, 21-23, 30, 37-39, and 41-45.

Entrance & outlet treatments/design. pp. 23-24, 30, 32, and 58.

Flared outlets/end sections. Manufactured end sections for culvert entrances and outlets. The end sections expand in width outward from the culvert end, are beveled to match the embankment slope, and have rounded corners at their outer ends. pp. 22, 25, and 37.

Floodwaters. Stream flows that have risen above the stream bank, and flow or stand over adjoining lands.

Floodwalls. Walls constructed of water-resistant material around the perimeter of a facility and extending above the design flood elevation to keep floodwaters away from the facility.

Flow deflectors. Triangular or circular structures installed on or immediately upstream from the footings of bridge piers to deflect the flow thereby reducing the flow velocities and preventing scour of the pier footings. pp. 61 and 62.

Flow diverters. Rock structures placed in a stream to divert the flow away from embankments. Usually designed to extend a short distance into the stream, flow diverters or barbs are higher at the edge of the embankment, and are tied into the bank to protect from erosion at their ends.

Flow full. The flow condition of a culvert when all of its cross-sectional area is carrying flow. In general, a culvert will flow full when its outlet is submerged (water surface is above the tope of the culvert outlet) or the depth of water above the top of its entrance is 1.5 times its diameter.

Flow partially full. A flow condition of a culvert when all of its cross-sectional area is not carrying flow. In general, a culvert will flow partially full when the water depth is above (or below) the top of its entrance and the water depth is below the top of its outlet.

Gabions. Wire baskets filled with rock and placed along embankments to prevent erosion.

Graded stream. A condition when a stream's bed is neither aggrading (sediment and/or gravel deposition is raising the bed) nor degrading (sediment and/or gravel erosion is lowering the bed). The stream is considered to be in equilibrium.

Head cutting. A condition when a stream's bed is progressively eroding (lowering) in the upstream direction.

'High head' conditions. Once a culvert is flowing full, an increase in the water surface elevation upstream from the culvert has a relatively small effect on the increase of flow through the culvert. The flow through the culvert is then described as being under "high head conditions."

High water marks. Lines found on trees and structures marking the highest elevation (peak) of the water surface for a flood event, created by foam, seed, or other debris.

High water overflow crossing. A depression in a road prism designed to carry flood flows from overbank areas. pp. 21, 23, and 28.

Hydrodynamic forces. Forces imposed on structures by floodwaters due to impacts of moving water on the upstream side of the structure, drag along its sides, and eddies or negative pressures on its downstream side.

Hydrostatic pressure. The pressure exerted in all directions by a given point in a body of water, usually caused by the weight of water overlying it.

Intermittent drainages. Streams that do not flow continuously.

Lining. Protective cover of the perimeter of a channel or the inside of a pipe. pp. 4, 5, 86, and 91.

Low water crossing. A depression in a road prism designed to carry flood flows from an intermittent drainage. pp. 23, 27, and 28.

Meander. In connection with streams, a winding channel usually in an erodible, alluvial valley. A reverse or S-shaped curve or series of curves formed by erosion of the concave bank, especially at the downstream end, shoals and bank erosions. Meandering is a stage in the migratory movement of the channel, as a whole, down the valley.

Overbank. The portion of the bank where the floodwaters flow above the historical confines of the bank.

Permeability. The ability of a material (generally an earth material) to transmit water through its pores when subjected to a pressure or a difference in head.

Realign piers & abutments. pp. 52, 56, and 57.

Relief culvert. Installed to mitigate debris plugging of culverts and bridges. Relief culverts may be installed at the culvert site at a higher elevation or at some distance from bridge openings.

Relief opening. This opening can be a culvert or bridge, or multiple culverts; normally located at natural side channels. pp. 56-58.

Replace multi-span bridge with single span. pp. 56 and 61.

Relocate. pp. 52, 72, 82, 95, and 99.

Revetment. Bank protection to prevent erosion.

Ring compression. Flattening of a circular culvert resulting from beveling its end to match the angle of the embankment. Flanges may be required to stiffen the beveled section of the culvert.

Riparian. Riparian areas occur next to the banks of streams, lakes, and wetlands, and include both the area dominated by continuous high moisture content and the adjacent upland vegetation that exerts an influence on it.

Riprap. Rock placed on embankment slopes to prevent erosion. pp. 13, 16, 98, and 99.

Roadway prism. The road embankment, shoulder, and surface.

Rounded inlet. The edges of a culvert entrance that are rounded for smooth transition, which reduces turbulence and increases capacity.

Scour. The result of an erosive action of flowing water, primarily in streams, excavating and carrying away material from the bed and banks. Wearing away by abrasive action.

Sediment. Road, gravel, or cobbles that originate from weathering of rocks and is transported by, suspended in, or deposited by water.

Spur dikes. Embankments that are designed to direct flood flows into a bridge opening.

Subcritical flow (tranquil and streaming). Low velocity stream flow. The flow appears to flow in tubes with uniform velocity.

Submerged. Covered with water. Here used as surface water elevations above the top of culvert entrances and outlets.

Supercritical flow (rapid and turbulent). High velocity stream flow. The flow appears to be shooting with varying velocity.

Wingwalls (treatment/design). Concrete walls constructed at culvert and bridge entrances and outlets to direct flows into their openings. Wingwalls may be constructed at angles up to 60 degrees from the culvert and bridge openings. pp. 21, 22, 25, 30, 35-37, 41-45, 49, 51, 52, 56-58, 62, and 66.

 
 

NOTE:  None of the mitigation measures in these Handbooks should be considered ‘pre-approved’ or otherwise automatically eligible for FEMA funding. Only FEMA staff can determine eligibility, once they have determined that an applicant is eligible and they have reviewed a project proposal.

FEMA HAZARD MITIGATION HANDBOOKS                                                                        Updated: June 13, 2002