Encyclopedia of Environmental Science and Engineering, Volume I and II

HYDROLOGY 483

same travel time. The outfl ow response for any level of fl ow

is therefore only dependent on y, which is a measure of stor-

age in the system. Following Henderson and Wooding’s

analysis of rainfall run-off,^26 the resulting run-off unit hydro-

graph would have a constant shape, which for the simplifi ed

situation is a simple triangle. Convolution of this triangular

hydrograph with the effective rainfall will again yield a typi-

cal outfl ow hydrograph. Very accurate data would be needed

to distinguish between this fi nal outfl ow hydrograph and the

result from the linear reservoir discussed earlier.

It therefore appears that the use of linear routing is not too

unreasonable. Further justifi cation will depend on the results of

watershed modeling which are discussed in the next section.

MODEL CALIBRATION AND ASSESSMENT

OF PERFORMANCE

Some examples of model calibration will be given for a region

in the Upper Columbia River basin (Figure 9). The watersheds,

such as the Jordan River and Spillimacheen, selected for cali-

bration purposes are deliberately of moderate size, some 200

to 500 km^2. Too small a watershed responds too quickly and

requires a data base time increment of a few hours, whereas the

size suggested above can be modeled using daily data. The cal-

ibration for these smaller watersheds forms an excellent basis

for modeling the larger watershed regions of several thousand

square kilometers used in forecasting mainstream fl ows.

FIGURE 9 Map of Upper Columbia basin (indicate Spill & Jordan)—Remove Goldstream.

C008_003_r03.indd 483C008_003_r03.indd 483 11/18/2005 10:29:30 AM11/18/2005 10:29:30 AM