New Mexico Geological Society Annual Spring Meeting — Abstracts

Complex distributed hydrologic models are widely used to understand flow and transport in watersheds and their effects on related physical and biogeochemical processes. These models typically discretize the watershed into elements for numerical simulation; however, this discretization is constrained by computational limitations, for example, the number of elements and their location. In this study, we investigate the effect that capturing key topographic features (e.g. rivers and ridges) has on the modeled flow and transport characteristics of a mountainous watershed. As a starting point, we use a simplified model that assumes steady state flow and a water table that is a subdued replica of the topography (i.e., Tóthian assumption). Then, we use different mesh resolutions, where the level of topography complexity is increased by capturing more stream channels and ridges. Modeled baseflow and residence time were used to quantify differences among complexity levels. Our results show that capturing the river network and ridges has a significant influence on simulated flow and transport patterns. For example, topographic complexity controls the proportion of baseflow generated from local, intermediate and regional flow paths. In particular, ignoring lower order streams diminishes flow through local flow systems and biases high the contribution of regional and intermediate flow paths. The proportion of baseflow from regional flow paths decreases with increasing topographic complexity. Similarly, this has an effect on residence time. The decrease of local flow, due to low topographic resolution, results in low-order streams with baseflow residence times biased high, affecting our ability to interpret environmental tracer data and predict bio- and geo-chemical evolution of water. Future work will relax the Tóthian assumption and include more realistic boundary conditions as well as geological features.