Regional Hydrologic Modeling to Support Water Allocation and Streamflow Management Across Diverse Watersheds in California

Benjamin Bowes; John Riverson

In recent years, numerous watersheds across California have experienced exceptionally dry conditions warranting state-of-emergency protections to ensure adequate, minimal water supplies for critical purposes. Given the increasing anthropogenic demand for water, the need to protect natural ecosystems, and the uncertainty in near- and long-term climate, there is a critical need for hydrological modeling and analysis tools that support comprehensive decision making and management of water supply, demand, and instream flow needs. This presentation will discuss some of the challenges surrounding sustainable water use and supply and introduce models and tools being developed for the State Water Resources Control Board Supply and Demand Unit for watersheds across California. A key component of supply and demand management is a robust watershed hydrology simulation platform. These hydrology models are built using the EPA’s Loading Simulation Program in C++ (LSPC) with a regionally consistent configuration and calibration approach; the models form the basis for short-term forecasting of available surface water and support decisions regarding water allocation to water rights holders. Several models throughout the state are being developed simultaneously, providing a unique opportunity to evaluate similarities and differences between the models and the watersheds being represented. During model development, there is a focus on specific functional flow components — the ecological building blocks of a healthy river — such as wet season peak flows and dry season baseflows. Using the models developed with this approach, the Supply and Demand Unit has a robust, consistent basis for evaluating management scenarios and informing decision making for surface water allocation.

Reproducible Hydrologic Model Building for Recharge Assessment Across Nevada’s Hydrographic Basins

John Volk; Chris Garner; Philip Gardner; Justin Huntington; Kip Allander; Murphy Gardner; Sayantan Majumdar

Quantifying groundwater recharge in the Great Basin is challenging due to complex hydrogeology, strong elevation-driven gradients, and sparse observations, yet increasing demand for defensible water budgets across Nevada’s hydrographic basins requires spatially and temporally distributed recharge estimates. We present the Nevada Water Initiative (NWI) Recharge Modeling Toolkit, a Python framework that automates generation of Precipitation-Runoff Modeling System (PRMS) models, which are distributed and physically-based hydrologic models, for Nevada’s hydrographic basins. The workflow draws on the NWI's “Data Bin,” that includes standard layers for the Great Basin of elevation, STATSGO soils, and LANDFIRE vegetation. The toolkit also retrieves PRISM climate forcings. It performs DEM conditioning, watershed discretization, stream network and cascade delineation, and parameter estimation to produce all inputs for PRMS models. Built-in diagnostic tools and software design enable transparent and reproducible iteration on model building choices. The toolkit requires little coding experience for standard model building workflows via a command line interface and a simple configuration file; however, it also includes an object-oriented Python interface for extending components and performing custom analyses. In addition to automated model builds, the toolkit includes utilities for evaluating PRMS-simulated recharge and summarizing water-budget components for comparison across basins, periods, and alternative configurations. Select results are shown for to NWI demonstration basins: Railroad Valley, a closed hydrographic system, and Pine Valley.

Integrated Hydrological Modeling of an Urbanized Mountainous Karstic Terrain

Yaakov Anker; Vladimir Mirlas; Alexander Gimburg; Michael Zilberbrand

Urbanized karstic watersheds present unique hydrological challenges due to the complex interaction between anthropogenic modifications and inherent karst features, including subsurface conduits, sinkholes, and rapid inhomogeneous infiltration pathways. Traditional watershed modeling approaches often fail to adequately capture these complexities, necessitating innovative data acquisition methods. Aerial and satellite remote sensing technologies have emerged as powerful tools for characterizing and monitoring these dynamic systems. Over the last two decades, Israel's central mountain rim has undergone rapid human development, marked by the establishment of several new towns, the expansion of existing cities, and the alteration of natural areas mainly for agricultural use and road construction. To evaluate the rapid change to natural watersheds across the region, integration of remotely sensed data with Geographic Information Systems (GIS) and hydrological models was applied for flood prevention assessment in one model city and groundwater recharge estimation was done for several major watersheds, including a comparison between natural and urbanized watersheds. Time-series analysis of satellite imagery enabled quantification of land use change impacts on watershed hydrology and a MODFLOW model enabled identifying changes in surface-subsurface connectivity patterns. The urban area hydrological modeling involved a modified HEC-HMS model that utilized the ModClark Transform and SCS Curve Number methods platform for a nominal urban watershed sub-basin analysis procedure, which enabled detailed urban runoff modeling. This integrated karstic terrain modelling procedure for predicting runoff volume and discharge can be used in water-sensitive design to maintain groundwater recharge and mitigate the negative impacts of runoff intensification.