Estimating Groundwater Budgets for Oregon

Overview:  

It is no secret that availability of groundwater is an increasing concern for many Oregon residents and resource managers. East of the Cascades, groundwater is a primary water source for agriculture, livestock, fish, wildlife, drinking water, and other uses. West of the Cascades, groundwater supplements more abundant surface water to fulfill these needs. To better understand and quantify this resource statewide, we are developing basin-scale groundwater budgets using consistent, modern methods.  

A groundwater budget accounts for water that enters and exits a groundwater system. The water entering the system - groundwater recharge - minus the water exiting – groundwater discharge - is the change in groundwater storage. Quantifying rates of recharge and discharge helps resource managers maintain a balance between water availability and demand.   

Fully developed statewide groundwater budgets are not possible with the data currently available. As a solution, we are making partial groundwater budgets, distinguished for upland and lowland areas where applicable. Partial groundwater budgets enable a comparison between the relative amount of groundwater withdrawals by humans and natural groundwater movement. 

For the purposes of this study, lowland areas are considered continuous valleys within the center of a basin. Upland areas are all other areas in a basin. Partial groundwater budgets will include estimates of: 

• Upland recharge from rain and snowmelt infiltration. 
• Groundwater flow from uplands to lowlands. 
• Base flow and streamflow runoff entering lowlands from upland areas. 
• Total surface water discharge exiting a basin and /or groundwater use from lowland phreatophytes. 
• Groundwater removal, where feasible, either from water rights allocation or published remote sensing data. 

This study is the first of two phases. The first phase utilizes the USGS’s National Hydrologic Model infrastructure with the Precipitation-Runoff Modeling System (NHM-PRMS) to develop preliminary estimates of groundwater recharge from infiltration of rain and snowmelt, and base flow for upland areas throughout Oregon. 

Phase I objectives: 

1. Validate an Oregon NHM-PRMS model -extracted from the National model- using existing groundwater recharge and discharge estimates and newly developed upland base-flow estimates. 
2. Recalibrate and improve the Oregon NHM-PRMS model using the latest base-flow estimates. 
3. Identify model and data deficiencies.
4. Compile and collect data needed for groundwater budget estimates and Phase II work.  

This is an active study with more information to come.