Drainage Design Manual - the City of San Luis Obispo

Berm. A levee, shelf, or bench along astreambank that may extend laterally in thechannel to partially obstruct flow, or parallelto the flow to contain the flow within itsstreambank. May be natural or constructed.Best Management Practice. A practiceused to reduce impacts from a particularland use.Biotechnical approach. An applied sciencethat combines structural, biological andecological concepts to construct livingstructures for erosion, sediment and floodcontrol.Blanket. Material placed on a streambank tocover eroding soil.Boulder. Sediment particle having adiameter greater than 256 mm (10 inches).Bridge. A structure for carrying traffic over awatercourse, depression, or other obstacle.Brush layer. Live branch cuttingscrisscrossed on trenches betweensuccessive benches of soil.Brush mattress. A mattress-like coveringthat is placed on top of the soil. Thecovering material is living wood plantcuttings that are capable of rooting.Buffer. A vegetated area of grass, shrubs ortrees to capture and filter runoff fromsurrounding land uses.CalTrans. California Department ofTransportation.Canopy. Overhead branches and leaves ofriparian vegetation.Canopy cover. Vegetation projecting over astream, including crown cover (generallymore than 3 feet above the water surface)and overhand (less than 3 feet above thewater surface).Capacity. The effective carrying ability of adrainage structure or facility. May also referto storage capacity.Carry Over. The quantity of water whichcontinues past an inlet.Catch Basin. A basin combined with astorm drain inlet to trap solids.Catchment Area. (1) The contributing areato a single drainage basin, expressed inacres, square miles, or other unit of area.Also called Drainage Area or Watershed. (2)The area served by a drainage systemreceiving storm and surface water; or by awater-course.Caving: The collapse of a streambank byundercutting due to wearing away of the oteor an erodible soil layer above the toe.Cellular Confinement. A design elementthat consists of a honeycomb-like structuralmaterial, placed to allow access across wetareas to distribute load and minimizeenvironmental damage, such as ruts.Channel. A natural or man-made waterwaythat continuously or periodically passeswater.Channel roughness. The irregularity ofstreambed materials sizes and channel formin plan and cross-section that causesresistance to flow.Channel scour and fill. Erosion andsedimentation that occurs during relativelyshort periods of time; degradation andaggradation apply to similar processes thatoccur over a longer period of time.Channel stability. A relative measure of theresistance of a stream or river to erosion.Stable reaches do not change markedly inappearance from year to year.Channel Storage. The volume of waterstored in a channel. Generally considered inthe attenuation of the peak of a floodhydrograph moving downstream.Check. A barrier placed in a ditch, canal orchannel to decrease the velocity of the flowof water so as to minimize erosion of thebottom and banks or to raise the level of thewater. Also used for diverting water fromone channel to another, as in irrigationusage.Check dam. A structure placed bank tobank downstream from a headcut.Clay. Cohesive soil whose individualparticles are not visible to the unaidedhuman eye. Soil can be molded into a ballthat will not crumble.Cobble. Sediment particles larger thanpebbles and smaller than boulders. Usually64 - 256 mm (3 to 8 inches) in diameter.Cohesive soil. Microscopic soil particlesthat have natural resistance to being pulledapart at their point of contact.Coir. A woven mat consisting of coconutfibers. Generally used for various soilerosion control practices such as surfaceslope protection and the construction ofgeogrids.Concentrated Flow. Flow which is alteredfrom its natural surface runoff and hasaccumulated into a single narrow ditch,channel or pipe.Conduit. Any pipe, arch or box throughwhich water is conveyed.