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<br />.,,, ....-, <br /> <br />0J1345 <br /> <br />16 <br /> <br />excess, stonn auration, etc.) as well as the watershed physiographic <br /> <br /> <br />features. This formulation relaxes the transform ulliqueness assumption <br /> <br />of the linear conceptual models. <br /> <br />The data requirements for developing similar regression equations <br />are tne same as the linear conceptual model requirements; the develop- <br /> <br />ment procedure, however, is different. The parameter(s) of the trans- <br /> <br /> <br />form function (K, or K and n) for watersheds with various percentages of <br /> <br />development are evaluated by minimizing the deviation between the <br /> <br />observed runoff hydrograph and the runoff hydrograph generated by the <br /> <br />linear transformation of the associated rainfall event. These parameters <br /> <br />are then related to the characteristics of the rainfall event as well <br /> <br />as the watershed's physiographic features by multiple regression analysis. <br />There is a good chance that the regional data required to generate <br />the regression equations of these conceptual rainfall-runoff models will <br />simply not be available. An alternative approach has been reported in <br />the literature (35, Bti) which suggests the testing of already developed <br />unit hydrograph formulae (such as Espey's equations) on any available <br />data within the stuuy region. If the tests yield satisfactory regen- <br />eration of observea hydrographs, then the full range of these equations <br />could be used (with caution) for the basin in question. <br />Physically-based rainfall-runoff models - Unlike the "black-box" <br />approach to conceptual modeling, physically-based rainfall-runoff <br />models attempt to approximate the physical processes occurring within <br />a watershed -- interception, evapotranspiration, infiltration, over- <br /> <br />land flow, and channel flow -- that convert rainfall into stormwater <br />runoff. The watershed under study is divided into hydraulically similar <br />drainage units (pervious flow planes, impervious flow planes, channel <br />