Discharge responses associated with rapid snow cover ablation events in the Susquehanna and Wabash River basins

ABSTRACT

In the mid-latitudes, snow plays a critical role in regional hydroclimate, with snow ablation variability in ephemeral regions representing an area of essential research. Due to a lack of historical snow-water-equivalent data in the eastern United States, recent research has substituted daily snow depth changes for ablation. These studies, however, do not explicitly examine if such a substitution yields a snowmelt hydrological signal, an important component of water resource management. As such, this study evaluates if ablation events, as defined as a daily snow depth decrease, subsequently result in increased river discharge within two similarly sized watersheds in the eastern United States: the Wabash and Susquehanna River basins. For both basins, >75% of snow ablation events resulted in a positive river discharge response (increase in discharge) at a 3-day lag. Furthermore, results show a significant and positive relationship between ablation event frequency and seasonal discharge response, such that an increase (decrease) in seasonal snow ablation event frequency yields an increase (decrease) in associated seasonal river discharge at a 3-day lag. These relationships indicate that inter-diurnal decreases in snow depth do carry hydrological implications, adding confidence that such a definition of ablation is appropriate for climatological applications.     

Evaluating precipitation products for hydrologic modeling over a large river basin in the Midwestern USA

ABSTRACT

We evaluated precipitation estimates, TRMM (Tropical Rainfall Measuring Mission 3B42V7), CFSR (Climate Forecast System Reanalysis), GHCN-D (Global Historical Climatology Network-Daily Version 3.24), and Daymet, using the Soil and Water Assessment Tool (SWAT). The suitability and quality of TRMM, CFSR and Daymet in forcing the SWAT-based hydrological model was examined by means of model calibration. A calibrated TRMM-driven model slightly overestimated streamflow, while a calibrated CFSR-driven model performed worst. The Daymet-driven model performance was as good as the GHCN-D-driven model in reproducing observations. In addition, the temperature was far less sensitive compared with precipitation in driving SWAT. TRMM 3B42V7 showed great potential in streamflow simulation. The results and findings from this study provide new insights into the suitability of precipitation products for hydrological and climate impact studies in large basins, particularly those in typical climates and physiographic settings similar to the Midwestern USA.     

Engineering geologic and geotechnical analysis of paleoseismic shaking using liquefaction effects: field examples

The greatest impediments to the widespread acceptance of back-calculated ground motion characteristics from paleoliquefaction studies typically stem from three uncertainties: (1) the significance of changes in the geotechnical properties of post-liquefied sediments (e.g., “aging” and density changes), (2) the selection of appropriate geotechnical soil indices from individual paleoliquefaction sites, and (3) the methodology for integration of back-calculated results of strength of shaking from individual paleoliquefaction sites into a regional assessment of paleoseismic strength of shaking. Presented herein are two case studies that illustrate the methods outlined by Olson et al. [Engineering Geology, this issue] for addressing these uncertainties.

The first case study is for a site near Memphis, Tennessee, wherein cone penetration test data from side-by-side locations, one of liquefaction and the other of no liquefaction, are used to readily discern that the influence of post-liquefaction “aging” and density changes on the measured in situ soil indices is minimal. In the second case study, 12 sites that are at scattered locations in the Wabash Valley and that exhibit paleoliquefaction features are analyzed. The features are first provisionally attributed to the Vincennes Earthquake, which occurred around 6100 years BP, and are used to illustrate our proposed approach for selecting representative soil indices of the liquefied sediments. These indices are used in back-calculating the strength of shaking at the individual sites, the results from which are then incorporated into a regional assessment of the moment magnitude, M, of the Vincennes Earthquake. The regional assessment validated the provisional assumption that the paleoliquefaction features at the scattered sites were induced by the Vincennes Earthquake, in the main, which was determined to have M7.5. The uncertainties and assumptions used in the assessment are discussed in detail.