New Tool Aims to Help Balance Supply and Demand of Water Resources

CARSON CITY, Nev. — A new computer model, developed by the U.S. Geological Survey, allows water managers to better manage water distribution of river basins with scarce and over-allocated water resources and account for complex interactions between groundwater and surface-water resources. The model is especially relevant during periods of low flow when water managers are tasked with balancing competing, and often diverse, interests.

“The development of this new modeling tool will help to better understand groundwater and surface water interactions in California's watersheds,” said Erik Ekdahl, Director at the California State Water Resources Control Board.  

The newly integrated MODSIM-MODFLOW computer model, cooperatively developed by the USGS and MWH Global, combines the river operations model MODSIM with MODFLOW, the world’s most widely used groundwater modeling program.

A distinct advantage of the MODSIM-MODFLOW integration, beyond the fact that it takes advantage of two long established models within their respective genres, is that the movement of information between the codes occurs several times within each simulated time step, thereby ensuring the model’s respective solutions are synchronized before moving on to the next time step. Because river operation models roughly approximate groundwater processes, non-synchronized solutions may lead to gaps in the water budget leading to inaccurate accounting of the available water resources.

“The integrated code takes an important step toward tightening the water balance in highly-regulated river systems,” said Eric Morway, lead USGS scientist on the model. “Synchronized solutions, ‘what-if’ scenarios, and/or future forecasts runs with an integrated model like MODSIM-MODFLOW more accurately account for the non-linear feedbacks and the cumulative effects of those feedbacks on yet unrealized operational decisions.”

In addition, the MODFLOW community now has access to new and novel functionality, allowing existing MODFLOW applications to be readily expanded. Conversely, MODSIM users can readily expand applications for more accurate representation of GW-SW exchange.

“This understanding is of critical importance given the State's new groundwater management laws, and how recent drought has significantly affected surface water and groundwater throughout California,” said Ekdahl. “This is timely and helpful step forward for those involved in the management for multiple uses of supply, wildlife and watershed health.”

Funded efforts are underway to apply the code in the Russian River, California, as well as in the neighboring states of Nevada (Carson River) and Oregon (Deschutes River). Groundwater-surface water interaction in these and other basins plays an important role in understanding current and future impacts on river operations, especially when considering the highly variable and uncertain nature of water supplies.

The model was published in the article "Toward improved simulation of river operations through integration with a hydrologic model" in the journal Environmental Modelling and Software.