MODELING THE GLACIAL MELTWATER CONTRIBUTION TO THE MIDDLE FORK NOOKSACK RIVER, WHATCOM COUNTY, WA, USING A DISTRIBUTED HYDROLOGY MODEL

In glaciated regions such as Washington's North Cascades, glacial meltwater is a vital component of rivers and streams and can be critical for municipal water supplies, power generation, and habitat issues. The Middle Fork of the Nooksack River is fed by meltwater from Deming Glacier on Mount Baker, WA. The City of Bellingham has been diverting water from the Middle Fork since 1962 to supplement the water supply, and to maintain water quality in Lake Whatcom, the water source for the city. The diverted water may contribute up to 80% of the surface inflow into Lake Whatcom during the summer and 20% of the city's yearly water consumption. Due to regulations, water is only diverted when the Middle Fork exceeds minimum acceptable streamflow. A concern for water resource managers in Whatcom County, WA is that Deming Glacier is retreating. Estimated changes in glacier areal extent in the North Cascades indicate that continued warming could lead to a decrease in glacial meltwater of up to 35%. In this study, the Distributed Hydrology Soils Vegetation Model (DHSVM) is used to perform a detailed assessment of the hydrology in the Middle Fork basin and to quantify future meltwater contributions to the Middle Fork Nooksack River as Deming Glacier continues to retreat.

The DHSVM is a physically based, spatially distributed hydrology model that simulates a water and energy balance at the pixel scale of a digital elevation model (DEM). The DHSVM requires multiple GIS input grids to characterize the watershed including a DEM, soil type, soil thickness, vegetation, stream network, and watershed boundary. All grids were formatted using ArcGIS software. Required meteorological input includes air temperature, relative humidity, incoming shortwave radiation, longwave radiation, and wind speed. Meteorological data were compiled from historical records of lower elevation weather stations. The model will be calibrated to measured stream discharge at the USGS stream gauge on the Middle Fork using a 1-hour time-step and 50m GIS grid resolution. I will present results of the initial model calibration.