Groundwater and Surface Water Interaction

For many coastal areas around the Puget Sound, the interplay between weather, surface water, soils, evapotranspiration and groundwater flows is critical to modeling stream flow and predicting quantity and timing of flows under climate change. In this presentation, we introduce an approach developed by the Suquamish Tribe that uses results from an existing USGS groundwater model for the Kitsap Peninsula to improve calibration of EPA’s VELMA eco-hydrology model that estimates changes in stream flow and biomass. We briefly describe how the VELMA model works and how the Kitsap Peninsula MODFLOW groundwater model worked. We describe a new groundwater capability recently added to VELMA 2.2, and explain how we used this with the results from the MODFLOW model to improve calibration of the VELMA model against observed gage readings. We show results for simulations for the Big Beef Creek watershed from 2000-2012. Finally, we discuss how this improved simulation model will be used to support decision making.

Impact/Purpose

One of the limitations of the VELMA modeling framework is that ground water aquafers are not simulated.  VELMA now has a simple ground water box and a means for diverting water to and from the box.  While not a complete solution, this will allow VELMA models to interact with models such as MODFLOW to model watersheds where ground water flow significantly effects surface water flow in streams.  This presentation is an initial use of this new feature.

Citation

Murphy, P., P. Williams, S. Hashisaki, A. Brookes, AND S. Chokshi. Groundwater and Surface Water Interaction. 14th Washington Hydrogeology Symposium, Auburn, WA, April 22 - 24, 2024.