Estimating groundwater pumping and return flow based on hydrologic recession analysis

Hydrologic processes have been affected by human activities which include both direct and indirect interferences. The indirect human interferences such as land use and land cover change have been studied and modeled in many watersheds around the world. These kinds of human interferences, resulting in land surface changes, usually affect the rising limb and the peak of a hydrograph. The streamflow recession process, are not much affected by the land surface condition and the impacts of indirect human interferences are trivial; however the direct human interferences such as water withdrawals and return flows may affect the recession dynamics significantly. Direct human interferences are difficult to observe and model, and are usually assumed to be known and additive to streamflow. This paper provides a recession analysis involving groundwater pumping and effluent discharge as variables. The analysis is applied to an urban watershed in the Chicago area. Based on the historical streamflow observation during the last half century, the analysis provides results that explain the impact of direct human activities on the streamflow recession process. Moreover, the analytical method allows retrieving human water use data such as groundwater pumping and return flow, which change with socioeconomic development and policy reforms, as long as the streamflow observation is available and long enough. The analysis is verified with the data of the case study watershed and can be applied to other watersheds under intensive human interferences.