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Regional flow estimation using a hydrologic model

University of British Columbia

The twelve watersheds analyzed in this study are heterogeneous in terms of drainage area, climate, topography, soil type, vegetation, geology and hydrologic regime, which indicates that any attempt at a statistical regionalization of streamflow characteristics for these watersheds would be unreliable unless based on a very large number of watersheds. Therefore, the hydrological behavior of these watersheds was analyzed using the UBC Watershed Model. The watersheds were calibrated until a maximized efficiency was achieved. A sensitivity analysis showed that the model was most sensitive to precipitation parameters and thus, precipitation was the most important factor. Given good precipitation data, the next most important parameter was found to be the fraction of impermeable area in the watershed. Therefore, several methods for estimating this parameter were examined and surficial geology maps gave the best results. Analysis of all the parameters for each watershed revealed that there was quite a consistent set of parameters for everything except the precipitation gradients and the fraction of impermeable area. Lack of variability of the parameters affecting the time distribution of runoff with watershed size supports the idea that the land phase controls the runoff process and the channel phase is secondary and appears almost negligible even for the watersheds larger than 1000 km² in size. Thus, the watersheds were re-run using the fixed set of parameters and inputting precipitation and fraction of impermeable area for each watershed. The results obtained by this simplified method were then compared with the results of the original calibration for each watershed. The comparison showed that this fixed parameter set provided reliable flow estimates, because the reduction in overall model efficiency ranged from 0 to 10%, and in most cases stayed within 5%. In addition, this set of parameters considerably simplifies model calibration, and is an excellent first step in obtaining a full calibration. Therefore, this method is very useful for estimating runoff from an ungauged watershed, provided meteorological input is available.

Thesis/Dissertation

application/pdf

2009-05-28

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http://hdl.handle.net/2429/8358

Civil Engineering

University of British Columbia

UBCV

DSpace