Minimizing Roadway Embankment Damage from Flooding (2016)

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80 GLOSSARY Aggradation—General and progressive buildup of the longi- tudinal profile of a channel bed from sediment deposition. Articulated concrete block—Concrete slabs that can move without separating mattress: as scour occurs; usually hinged together with corrosion-resistant cable fasteners; primarily placed for lower bank protection. Backfill—Material used to refill a ditch or other excavation, or the process of doing so. Bedrock—Solid rock exposed at the surface of the earth or overlain by soils and unconsolidated material. Discharge—Volume of water passing through a channel during a given time. Downstream slope—Embankment slope that would be reached by water only if the embankment were overtopped. Embankment—A raised earth structure on which the road- way pavement structure is placed. Erosion—Displacement of soil particles from water or wind action. Floodplain—A nearly flat, alluvial lowland bordering a stream, that is subject to frequent inundation by floods. Freeboard—Vertical distance between the level of the water surface at design flow and a specified point (e.g., a bridge beam, levee top, location on a highway grade). Gabion—Basket or compartmented rectangular container made of wire mesh. When filled with cobbles or other rock of suitable size, the gabion becomes a flexible and perme- able unit with which flow- and erosion-control structures can be built. Geomorphology—That science that deals with the form of the earth, the morphology: general configuration of its surface and the changes that take place as a result of ero- sion and deposition. Headwater level—Level of water at the upstream of the embankment. Hydrograph—Graph of stage or discharge against time. Hydrology—Science concerned with the occurrence, distri- bution, and circulation of water on the earth. Landside slope—Embankment slope that faces land in a coastal environment. Levee—Embankment that plays a flood control role and pre- vents overflow from the wet side to the dry side. Meandering stream—Stream having a sinuosity greater than some arbitrary value. The term also implies a mod- erate degree of pattern symmetry, imparted by regularity of size and repetition of meander loops. The channel gen- erally exhibits a characteristic process of bank erosion and point bar deposition associated with systematically shifting meanders. Rapid drawdown—Lowering the water against a bank more quickly than the bank can drain without becoming unstable. Riprap—Layer or facing of rock or broken concrete that is dumped or placed to protect a structure or embankment from erosion; also the rock or broken concrete suitable for such use. Riprap has also been applied to almost all kinds of armor, including wire-enclosed riprap, grouted riprap, sacked concrete, and concrete slabs. Roadway—Portion of a highway, including shoulders, for vehicular use. (A divided highway has two or more roadways.) Runoff—That part of precipitation that appears in surface streams of either perennial or intermittent form. Seaside slope—Coastal embankment slope that faces the sea. Seepage—Slow movement of water through small cracks and pores of the bank material. Tailwater level—Water level at the downstream of the embankment. Upstream—Side of the embankment from which water flows.