SIMPLIFICATIONS OF WATERSHED GEOMETRY AFFECTING SIMULATION OF SURFACE RUNOFF
In formulating the equations describing the flow of water on the surface of a watershed, geometric simplifications must be made. A geometric simplification is the substitution of a simple geometry for a more complex one. The problem is to examine techniques for and consequences of such simplifications, and thereby develop objective procedures for geometric simplification of complex watersheds. Watershed geometry is represented by a series of planes and channels in cascade. When overland flow and openchannel flow in the cascade are described by the kinematic wave equations, the resulting mathematical model is called the kinematic cascade model. Planes are fitted to coordinate data from topographic maps by a leastsquares procedure. Residuals of this fit form a geometric goodnessoffit statistic as the improvement over using the mean elevation. Channel elements are determined, using Gray's method, as the slope of the hypothenuse of a right triangle with the same area as that under the observed stream profile. The ratio of the altitude of this right triangle to the total relief of a stream is the index of concavity, a channel goodnessoffit statistic. An overall goodnessoffit statistic is the drainage density ratio, the ratio of drainage density in the cascade of planes and channels to drainage density of the watershed. The mean value of a hydrograph goodnessoffit statistic, as the improvement over using the mean discharge, increases as the geometric goodnessoffit statistic increases but also decreases as the drainage density increases. A combined goodnessoffit statistic, the product of the drainage density ratio and the geometric goodnessoffit statistic, is related to the degree of distortion in optimalhydraulic roughness parameters. Distortions in watershed geometry result in optimal roughness parameters smaller than the corresponding empirically derived values for simple watersheds where less distortion is involved. /Author/

Corporate Authors:
Elsevier Science
Radarweg 29, P.O. Box 211
1043NX AE Amsterdam, Netherlands 
Authors:
 Lane, L F
 Woolhiser, D A
 Publication Date: 197710
Media Info
 Features: Figures; References;
 Pagination: p. 173190

Serial:
 Journal of Hydrology
 Volume: 35
 Issue Number: 1/2
Subject/Index Terms
 TRT Terms: Channel flow; Drainage; Kinematics; Least squares method; Mathematical models; Runoff; Simulation; Streams; Watersheds
 Uncontrolled Terms: Open channel flow
 Subject Areas: Highways; Hydraulics and Hydrology;
Filing Info
 Accession Number: 00165213
 Record Type: Publication
 Files: TRIS
 Created Date: Nov 23 1977 12:00AM