Laserfiche WebLink
<br />URBAN HYDROLOGY <br /> <br />Definition and Role in Planning <br />The role of urban hydrology in planning for stormwater management <br />is that of forecasting streamflow temporally and spatially throughout <br />the urban watershed for use in establishing performance objectives and <br />developing and evaluating alternatives. Urban hydrology refers to the <br />technical analysis that is applied in order to develop the needed hydrologic <br />information. <br /> <br />, Rainfall-Runoff Process <br />The process of urban storm ruhoff can be conceptualized by following <br />the movement of precipitation onto and through a watershed. During a <br />storm event, precipitation falls upon a watershed in widely varying total <br />'amounts and rates, Each component of precipitation input to a basin is <br />partitioned at the interface with the surface of the ground into surface <br />runoff that may be termed overland flow'and infiltration. The precipitation <br />that infiltrates through the soil is "lost" to surface runoff, although in <br />a few cases it may appear later in storm runoff. The overland flow accretes <br />into small rivulets that grow into small drainage channels, then larger <br />ones. The smaller and larger rivulets continue to aggregate into major <br />channels and eventually into streams. <br />Water must have depth in order to flow and, as a consequence, some flow <br />is temporarily stored o~ the surface of the watershed. This storage, termed <br />natul'al storage, has an attenuating effect on runoff rates, In well developed <br />natural watersheds there are many smaller and larger streams that provide <br />considerable natural storage, In their natural state, the channels are <br />7 <br />