DEVELOPING A WATER BUDGET FOR MORGAN VALLEY, MORGAN COUNTY, UTAH

Morgan Valley is a rural area characterized by extensive agricultural activity and increasing population in the Wasatch Range of northern Utah. The purpose of our study is to develop a water budget for the Morgan Valley drainage basin.

The inflow component in Morgan Valley consists of precipitation and streamflow crossing into its drainage basin. We used PRISM precipitation grids to get rates and distribution of precipitation. The 10-year (1998-2007) weighted average precipitation rate is estimated at 26.4 inches per year, which is equivalent to 436,000 acre-feet per year. We estimated the 10-year average stream inflow via the Weber River at Devils Slide at 190,000 acre-feet per year using linear regression. Stream inflow at East Canyon Creek has a 10-year average of 35,000 acre-feet per year. Thus, the total inflow into Morgan Valley is 661,000 acre-feet per year.

The outflow component in Morgan Valley consists of evapotranspiration, stream outflow from the Weber River at Weber Canyon and Gateway canal, and water used for municipal and industrial purposes. We estimated the average evapotranspiration (ET) based on current water-related land use and natural vegetation patterns. The ET volumes are integrated by multiplying the acreage of each land use and natural vegetation pattern by its specific ET rate. We estimated average ET consumed by irrigated agriculture at 28,400 acre-feet per year, and ET consumed by natural vegetation at 228,000 acre-feet per year, for a total ET of 256,400 acre-feet per year. The 10-year average outflow measured at the Weber River streamflow station at Gateway is 249,000 acre-feet per year and the water diverted to the Gateway canal/tunnel is measured at 93,000 acre-feet per year, for a total stream outflow of 342,000 acre-feet per year. Water outflow used for municipal and industrial purposes is estimated at 1600 acre-feet per year. Thus, the total outflow from Morgan Valley is 600,000 acre-feet per year. The 61,000 acre-feet per year difference in inflow/outflow does not necessarily represent water available for additional use. The water budget imbalance may result from estimation errors in precipitation, evapotranspiration, or streamflow from the Weber River at Devils Slide, and/or number rounding.