MS Thesis Defense


Xiang Li
Masters Student, Water Resources Science

December 19, 2019


Drainage Timescale Estimates and Storage Change Analysis on a Basin Scale

The groundwater travel time depicts the characteristic timescale of the catchment drainage process and is therefore also known as drainage timescale ( K ). On account of the difficulties modeling groundwater system, it brings necessity for the research on K . Catchment drainage timescale could be calculated empirically from recession flow analysis as well as from hydraulic theory. Applicability of K is critical in groundwater hydrology, such as, estimation to groundwater storage change. Groundwater storage change estimation helps access risks for potential flood and droughts. It also provides action guidelines for water managers to adjust water needs under the increasingly intense population pressure. This thesis conducts two researches based on K . K is derived for 17 HUC-8 watersheds in central Minnesota. First, the unknown agreement between empirically obtained drainage timescales and the groundwater theory is confirmed statistically. A satisfactory statistic result and the interpretation are obtained showing the general agreement of the K obtained from the recession analysis and the groundwater theory expression. Although the aquifer thickness’ contribution to regression results are inexplicit, the relationship strength of stream length, watershed drainage area, aquifer slope and aquifer transmissivity against K is characterized by statistical coefficients and signs. Second, applicability of K in annual groundwater storage change estimate is validated with a unique approach, which computes groundwater storage change innovatively by interpolating water levels’ temporal deviations. An overall agreement confirms the applicability of K in annual groundwater storage change analysis and minor inconsistences are explained by the interpolation data.