The Entiat Experimental Forest: A Unique Opportunity to Examine Hydrologic Response

Water is generally regarded as the most important natural resource in the interior Columbia River basin (ICRB). Public agencies managing forested headwater source areas are under increasing pressure to document water quantity and quality, and the effects of background and anthropogenic disturbances that influence them. Fire is widely recognized as the primary disturbance process affecting ecological systems in the ICRB. For these reasons land management agencies seek a more complete understanding of processes that generate and maintain streamflow as well as effects of fire and post-fire treatments on water quantity and quality. Although effects of wildfire are issues of major concern, they remain poorly understood at the catchment scale, largely because site specific data from both before and after wildfire are rare. The Entiat Experimental Forest (EEF) in central Washington State provides this type of hydrologic record of fire effects, owing to a severe wildfire during the summer of 1970, following ten years of stream gaging as part of a controlled land use experiment. Data collection continued after the fire through 1977. The entire dataset provides an archive for assessment of hydrologic response and model formulation, calibration, and testing. Research at the EEF is being revived to model effects of fire on water quantity and quality, including effects on water source, flowpath, timing, and post-fire recovery of hydrologic processes. We are taking a diagnostic approach to gaging to understand internal catchment behavior and develop a functional characterization of the EEF catchments. Change detection modeling employing the Hydrologiska Byrins Vattenbalansavdelning [HBV] rainfall-runoff model is being applied by: (1) comparing observed runoff to runoff simulated from pre-fire parameters, (2) comparing simulations based on pre-fire parameters to simulations based on postfire parameters, and (3) directly contrasting re-fire with ~ost-fire parameter values. Preliminary modeling results suggest that effects of the 1970 fire included greater snow accumulation, earlier initiation of snowmelt runoff at lower mean air temperatures, more rapid melt, increased soil moisture, and sharply increased runoff. Gaging at other catchments in the larger Entiat River subbasin creates a foundation for nested watershed monitoring and modeling to address spatially distributed hydrologic processes in this portion of the ICRB.