Twin Cities WRS Seminar

Quantifying Terrestrial Water Storage in Central MN


John Nieber
Dept. of Bioproducts and Biosystems Engineering

September 13, 2019


The water stored in lakes, wetlands, streams, soil, and groundwater plays a critical role in the functioning of the ecosystems of the earth and human well-being. In the past two years we have been developing estimates of terrestrial water storage in a region spanning from the Twin Cities Metro to Moorhead. The region contains 17 HUC-8 watersheds. Estimates of water storage were made using several sources of information and associated different methods. First we estimated terrestrial water storage using water table levels in observation wells, soil moisture monitoring sites, lake levels, and the data from the national wetland inventory. Water level data from wells in conjunction with lakes was used with interpolation methods to estimate water table levels across the study region, and from that water storage was estimated using porosity estimates for the quaternary geology. Lake volumes were estimated using a model that applies lake surface area with the topography surrounding a lake. Soil moisture was estimated using thickness of the unsaturated zone and assuming field capacity conditions. Storage in wetlands was estimated using the wetland areas mapped within the national wetland inventory. Second, we applied water balance models on a (HUC-8) watershed scale with estimated precipitation, actual evapotranspiration, and streamflow. Third, we used satellite data, including data from the GRACE satellite and LANDSAT satellite. All estimates were derived on monthly and annual bases. Estimated changes in water storage with time (monthly, seasonal, or annual) were found to be consistent across these different approaches. It is hoped that the methods applied and tested will be of assistance in water management decision-making, and to provide data for hydrologic and ecosystem models.