New Mexico’s Mountain Sources of Water: A Mechanistic Approach to Understand Mountain Recharge and its Implications for Local and Statewide Water Budgets
Jesus Gomez-Velez, Chao Wang
We investigate the controlling mechanism of stream network structure, topography, geology and climate in hydrological processes and recharge in mountainous watersheds. The first part of the work explores in detail the importance of capturing key topographic features for modeling groundwater flow and transport in mountainous watersheds. We simulate baseflow, mean age, and the concentration of solute from subsurface chemical weathering for different levels of representation of streams and ridges in the mesh. The topography complexity level (TCL), a measure of our ability to resolve topographic features, is increased progressively by refining the mesh along more streams and ridges of lower Horton-Strahler orders. Our results show that TCL controls the proportion of baseflow generated from local, intermediate and regional flow paths. Ignoring lower-order streams or ridges diminishes flow through local flow paths and biases higher the contribution of intermediate and regional flow paths. Consequently, it results in baseflow mean age being biased older. The magnitude of the bias increases for systems where permeability rapidly decreases with depth giving the dominance of shallow flow paths. Based on a simple geochemical model, the concentration of weathering product is less sensitive to the TCL due to the thermodynamic constraints on chemical reactions. Interestingly, slowly depth-decaying permeability enhances, while rapidly depth-decaying permeability diminishes, the effect of TCL on solute concentration, due to the change of the relative magnitude of mean age and chemical equilibrium time. The second part of the work uses synthetic watersheds to explore the controlling mechanism of the landscape structure on groundwater flow and transport, baseflow generation, and recharge estimation. Preliminary results show that channel network and topographic structure can significantly influence the spatial distribution of baseflow across stream order, and the recession rate of baseflow. Our results will improve baseflow recession analysis, which is a critical step in building parsimonious recharge
estimation models based-on watershed storage-discharge relationships.
Keywords: Groundwater recharge, topography, stream network structure, geology, climate, mountainous watersheds