North Fork Blackfoot River Hydrology Study

DNRC Report WR-3.C.2.NFB
March 2001

Abstract

A recent completed study conducted by the Montana Department of Natural Resources and Conservation (DNRC) assessed the hydrology of the North Fork Blackfoot River in its lower reaches near Kleinschmidt Flat. Reaches along the lower river and some of its tributaries experience seasonal water shortages that may impair fisheries and affect irrigator’s ability to use their water rights. Instream flow and irrigation demands for this water make it imperative to have an understanding of the hydrology of the area and how it interacts with multiple land uses.

The study characterizes the general hydrology of the Kleinschmidt Flat area and focuses on identifying areas where natural and anthropogenic factors impact surface and groundwater interactions and ultimately instream flows of the North Fork Blackfoot River and its tributaries Rock Creek, Salmon Creek, and Kleinschmidt Creek. Monitoring surface water inflows and outflows, diversion ditch efficiency, and groundwater levels was conducted over several irrigation seasons.

Study results indicate what area residents have long suspected. The North Fork Blackfoot River, Rock Creek, Salmon Creek, and most of the irrigation ditches lose large amounts of water into permeable soils in the upper three-quarters of Kleinschmidt Flat. As well, the considerable amount of return flow observed in the lower quarter of the flat appears directly linked to the inefficient delivery systems and instream flow losses due to seepage. The available data suggests an average of about 30 cfs is diverted from the North fork Blackfoot River, Salmon Creek, and Rock Creek during the irrigation season. With crop water requirements of less than 15 cfs, it is apparent that improvements in water conveyance and irrigation application methods on existing acres could result in additional water available for instream flow in dewatered sections of the river.

Information presented in this report has and will be used to provide a scientific basis for making water management decisions that will not only increase water use efficiency among landowners, but enhance instream flows as well.

For a copy of this document contact:

Mike Roberts
DNRC Water Resources Division
1424 9th Avenue
P.O. Box 201601
Helena, Montana 59620-1601
(406) 444-6641
miroberts@mt.gov