Chapter 3: Plumbing the Gallatin - Water Supply and Distribution

This section contributed by Scott Compton, DNRC

The Gallatin’s landscape is a product not only of its great natural streams and springs, but also a result of the intricate network of water diverted, pumped and channeled around the valley. The “engineered watershed” determines to a large part where people can live and which land is most productive.

Public Water Systems

The largest system supplying water for household and commercial use in the Gallatin is the Bozeman system. This system supplies slightly less than half of the people (about 26,000 in 1998) living in the watershed. Bozeman draws water from three sources: Bozeman Creek, Hyalite Creek (and Hyalite Reservoir), and Lyman Creek. The water from Bozeman and Hyalite Creeks is piped to a water treatment plant south of Bozeman. The Lyman Creek supply consists of a spring box water collection system supplying Lyman Creek Reservoir, located northeast of Bozeman. The quality of water from Lyman Creek is such that it receives only chlorination and fluoridation. The water is delivered to three water storage reservoirs (Sourdough, Hilltop, and Lyman Creek) and is supplied to the distribution system through two principal transmission systems. The distribution system consists of approximately 120 miles of water mains, ranging from 4 to 24 inches in diameter.

Projected Annual Water Use for Bozeman

Source: MSE-HKM Engineering

Text description of projected annual water use for Bozeman. Includes a larger image of the chart.

* Million gallons per year
** Also referred to as Bozeman Creek
*** Also referred to as Hyalite Creek
¹ Reliable yield = the amount of flow actually available given natural fluctuations and other existing rights
Source: MSE-HKM Engineering, Bozeman Water Facility Plan

Bozeman, like many cities, has two separate urban drainage systems. The water that is used in homes is carried away by sanitary sewers and treated before being discharged to the East Gallatin. The normal low flow of this system is about 3 million gallons/day, with a current capacity of around 5.78 million gallons/day. Bozeman’s wastewater treatment plant is a “tertiary” treatment facility, meaning that advanced processes are used to effect greater removal of pollutants. An entirely separate system, the storm sewer, handles snow and rain runoff from streets. Most of this water is carried to detention ponds to settle prior to discharge to ditches and streams, but some older lines flow directly into creeks and ditches flowing to the East Gallatin.

Belgrade is supplied by groundwater. Four wells yield approximately 4.3 million gallons/day, serving approximately 5,400 people. Stormwater is released to the soil through percolation from a system of drains. Belgrade’s sanitary sewage is settled in storage lagoons, aerated, and clarified, but does not receive advanced waste treatment. This is known as “secondary” treatment. Unlike Bozeman, Belgrade wastewater is not discharged to a river. Residue is disposed of on land.

Manhattan, by comparison, receives its supply through both wells and a spring. Manhattan is permitted to discharge treated sewage into the Gallatin River.

Big Sky differs only from the city systems in that it is run as a county water and sewer district. Wells at the mountain ski area and at the Meadow Village supply approximately 800,000 gallons/day, serving some 2,400 single family homes. This involves about 6,000 people at peak use. A small stormwater system collects runoff from the mountain mall. Sewage is treated, stored, and land-disposed by spraying.

Private Domestic Water Sources

There are approximately 30 other “community” water systems that together supply domestic water to some 4,000 people in the watershed. Community wells are centralized private well systems that connect to multiple users, some with as many as 400 users. All of these systems are supplied by groundwater. Individual wells supply domestic water for almost all rural households. As of March 1998, there were 9,500 wells on record in the watershed, of which approximately 75 percent had filed water rights.

Irrigation

Many canals and ditches crisscross the valley, delivering water for irrigation. Of the water taken from the main stem of the Gallatin, most is diverted between the mouth of the canyon and Four Corners. These diversions have water rights that essentially capture the entire flow of the river until return flows recharge the lower Gallatin below Four Corners. However, cooperation between the court-appointed Water Commissioner and irrigators has prevented the river from being totally dewatered in the past.

Man-made watershed feature.

Irrigated Acreage in Gallatin County
1952-1996

Soure: Slagle 1995; USDA Montana Agricultural Statistics 1997.

Text description of irrigated acreage in Gallatin County. Includes a larger image of the chart.

Source: DNRC

In the Gallatin, most canals and ditches are privately owned and managed by local irrigators. One exception is the Middle Creek Water Users’ Association, a non-profit corporation that manages some storage rights to Hyalite Reservoir, a state-owned project.

Reservoirs

There are approximately 130 reservoirs in the watershed, the largest being Hyalite Reservoir, which stores some 10,100 acre-feet of water. Most small reservoirs in the Gallatin have a recreation/fishing aspect to their use. Pond construction for recreation and aesthetic purposes by private landowners with access to water is increasing.

Water Supply

Overall, water supplies in the Gallatin are good. Large quantities of groundwater exist in the central valley, although some foothills areas have experienced declines in groundwater level at times. The latter is likely due to poor recharge of local groundwater sources. Despite conversion of many areas in the valley from agricultural land to subdivisions, depth to groundwater has not changed significantly from 1950 to the present. Increased depth to groundwater would be indicative of depletion of the aquifer.

Surface-water supply depends on the yearly snowpack and rainfall. Low water years may cause water rights to be cut off sooner than usual and affect some crop production. On the other hand, Hyalite Reservoir is, statewide, one of the DNRC’s most consistent suppliers of water.

While supplies of water are physically available in the Gallatin, new rights for consumptive purposes are not legally available. The Gallatin is one of several rivers in the upper Missouri Basin closed to new withdrawals (see Chapter 4).

Water for the Next Century

As the valley’s population increases, the question of how to quench its growing thirst looms larger. Growing Bozeman will reach several milestones in the next few decades, as it exceeds the existing capacity of its water treatment and distribution infrastructure and, ultimately, the maximum reliable yield of its current water supply. Absent a change in efficiency or conservation measures, Bozeman will exceed its current water supplies by 2042. Bozeman continues to look into acquiring direct flow rights as they become available, and the city is examining the feasibility of rebuilding a reservoir in the Bozeman Creek watershed that was breached in the 1980s. Conservation of water will no doubt play a role in determining Bozeman’s water supply future, as will education, regulation, and changing rate structures.

While groundwater appears to be plentiful in most areas, changes in land use may affect irrigation practices. Water losses from conveyance ditches have a major effect on recharge of the valley’s aquifer. As subdivisions replace flood-irrigated fields, local water tables could drop in some areas and rise in others. The biggest threat growth may pose to groundwater is the contamination from individual septic systems in high-density developments and from localized chemical spills.

Get more facts about the Gallatin at the Environmental Protection Agency Surf Your Watershed web site.

Annualized Daily Water Budget for the Gallatin Surface Water Inflow = 714.2 million gallons per day (MGD) Withdrawals: Irrigation Water Withdrawal = 420 MGD Public Water Supplies = 5.4 MGD Commercial = 1.2 MGD Domestic = 4.2 MGD Return from Wastewater Discharge = 4.4 MGD Source: USGS

Information

Groundwater Information Center, Montana Tech, Butte
(406) 496-4336
DNRC Bozeman Regional Office
586-3136
US Geological Survey, Helena
(406) 441-1319
City of Bozeman, Water Facility Plan for Bozeman, Montana, MSE-HKM Engineering, Nov. 1997
582-2300

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