Water Balance

Balancing the Water Budget

“I’m often asked ...is there enough water in the valley to meet everybody’s needs? ...the simple answer is yes.”
- Alan English, District Manager, Gallatin Local Water Quality District

When posed directly with the question “Is there enough water in the Gallatin Valley to support population growth and new development and continue to support agricultural interests?”, English’s response, while more elaborative, is the same. He explains, “Yes, if we jointly manage our use of both surface waters and ground waters. This management must focus on minimizing declines in ground water levels due to new ground water pumping and loss of artificial recharge from historic irrigation practices.  At the same time we must also protect existing agricultural water rights and our rivers, streams, and wetlands. 

In the Gallatin Valley there are sufficient agricultural surface water rights that can be transferred to new domestic uses or used to augment new ground water pumping for domestic purposes to achieve our overall goal of all water users while supporting new growth.”  (Alan English, August 8, 2007)

GALLATIN VALLEY WATER BUDGET NARRATIVE
By Alan English, Manager, Gallatin Local Water Quality District

An estimate of the annual amount of water that moves into and out of the Gallatin Valley was made using existing information available in 2001.  Water flow into the valley comes from the West Gallatin River, tributary streams, ground water flow, and direct precipitation. With few exceptions, almost all of the water that leaves the valley exits as surface water flow at Logan, enters the atmosphere by evaporation, or is evapotranspired by native plants and crops.  The budget assumes that in the long-term ground water levels remain fairly constant and ground water recharge and discharge are in balance.

The amount of water flowing into the valley from the West Gallatin River is well documented by the USGS gauging station at Gateway.  Surface water flow out of the valley is well documented by the USGS gauging station at Logan.  The USGS Water Resources report by Hackett (1960) was used to estimate tributary flow, direct precipitation, and ground water flow into the valley.

Estimates of the amount of consumptive use of water by cities, towns, small public water systems, and private wells were based on information obtained from public water systems and from well records.  The losses of water from the valley that are attributed to agriculture, native plants, and direct evaporation were based on the 1953 Water Resources Survey completed by the Montana State Engineers office (1953), and Hackett (1960).

Based on the estimates used, the overall water balance appears reasonable, with an error of about 1.5%.  While the numbers used to develop the water budget have errors, and need updating, the budget still shows what the general magnitude of the different sources of water into and out of the Gallatin Valley are, and what the primary consumptive uses of water are.