Investigating scaling effect on subsurface runoff in the Ohio River Basin

Abstract:

Issues associated with hydrological scaling has been investigated for decades, and as model scales continue to approach process scales, our hydrologic understanding gained from model assessment and sensitivity analyses continues to grow. However, the data and computational requirements to operate at relevant process scales still represent significant challenges, especially in the context of regional and global modeling. Here we investigate a space-time strategy which enables subsurface runoff routing processes to be upscaled to coarser model scales while maintaining event hydrograph peak discharge and timing characteristics. A case study in the Ohio River Basin (roughly 500,000 km²) is presented using a synthetic 1 cm 30 days runoff experiment. The method combines statistical and physically-based Hillslope River Routing (HRR) modeling techniques. Cumulative Probability Distributions (CDFs) for subsurface flowpath travel times based on 90-m topographic data and conceptualized model units representing individual catchments in the (HRR) model are equated by adjusting hydraulic conductivity along HRR hillslopes. Based on the 90-m digital elevation model (DEM) data, The CDF travel time for individual catchments are approximated by the beta distribution to reduce processing time for large watersheds. Nine model scales are investigated: 1, 3.2, 10, 32, 100, 320, 1000, 3200 and 10000 km², where model scale represents the threshold areas used to define the underlying river network and catchment boundaries. In this study, the reference scale is set to 1 km². A correction coefficient is applied to the whole basin to overcome limitations associated with catchment shape and discretization assumptions in the HRR model. Simulated hydrographs at the outlet of the Ohio River Basin for the eight coarser model scales have peak discharge and time-to-peak discharge values that are nearly identical to the reference scale model.