Mapping Runoff by the Grid Square Technique

Abstract

Runoff is a difficult variable to map because the information from river gauging stations only indicates average runoff from the catchment area above the gauging point. A method of mapping runoff by grid-based extrapolation of two components of the water balance equation (evapotranspiration and precipitation) and application of a runoff model in each grid square, is suggested as a means of overcoming many of the problems related to runoff mapping.

Uncertainty analysis of runoff estimates from runoff-depth contour maps produced by five automated procedures for the northeastern United States

“…Values are then extrapolated to the other grid cell sites and, after minor refinements based on withheld data, a map is produced (Solomon, et aL, 1968). A variant method is to use estimated precipitation and ET in a water balance formula developed by Penman that employs a soil moisture component to estimate runoff (Foyster, 1975). The grid square method's main strength is the ease with which estimated discharge of a stream can be calculated by using the estimated runoff for the grid cells in the watershed and the grid size.…”

“…The weakness of this technique is the generalizations that will occur due to the use of a uniform grid over an amorphous drainage pattern. Calculating from Foyster's (1975) estimated values for five sites in southeast England from one application of this technique, estimated discharge varied from -7 to + 16% of actual measured discharge with a mean error of 5.43% and a standard deviation of 9.50%.…”

“…At the scale of this study the area of the watershed compared to the study area is small and thus it was felt appropriate to treat the areal runoff values as points (Foyster, 1975). The runoff sites are placed in the center of their appropriate drainage basin, as opposed to the actual gage site, in accordance with standard USGS runoff-depth mapping policy (Graczyk, et al, 1987, Krug, et al, 1990.…”

“…Geographers and hydrologists have utilized several methods to produce runoffdepth contour maps (Langbein, et al, 1949, Thornthwaite, et al, 1958, Solomon, et al, 1968, Liebscher, 1972, Foyster, 1975, Krug, et al, 1990 but the predominate method of mapping runoff is with manual methods (e.g. Krug, et al, 1990).…”

“…Automated methods to map runoff-depth have been developed (e.g. Solomon, et al, 1968, Foyster, 1975, but none are widely used.…”