Title
Watershed Assessment & Conservation Options for Ambrose-Three Mile Creek in the Bitterroot Basin
Abstract
The State of Montana lists Ambrose-Threemile Creek of the Bitterroot River basin on its bi-annual 303(d) list as impaired by degraded water quality and aquatic habitat. A two-year watershed project assessed stream and riparian conditions and made recommendations for improvements. Work was funded by MDEQ under the 319 Non-point Source Pollution program, and many partners cooperated. The project’s purpose was to improve water quality and habitat for native aquatic life and wildlife while continuing to support agricultural uses of water. Improvements are expected to reduce nutrient and sediment loads to the Lee Metcalf National Wildlife Refuge and Bitterroot River. Project objectives were: 1) assess stream conditions; 2) develop community interest and support; 3) develop a long-term restoration program; and 4) support a stakeholder group capable of a sustained watershed restoration effort.
Three Mile Creek is a third-order stream with hydrology characterized by mean daily flows of 15-17 cfs and estimated bank-full flows of 10 cfs in Ambrose Creek, 25 cfs in upper Three Mile Creek, and 50 cfs near the outlet. Geology and soils of the watershed are important aspects of water quality problems. Land ownership is 64% private. Land cover is >55% lightly vegetated lands.
Mountain stream reaches were straighter & had lower width/depth ratios than typical. In foothills and valleys, channels were incised with vertical eroding stream banks and unstable channel forms. Stable reaches have <2% eroding banks, while reaches with disturbances have >5% and sometimes >10% eroding banks. Stream substrate in reference reaches is <45% fine material, while disturbed reaches have 55%-90%. Aquatic habitat is diminished by loss of pools, low quantities of woody debris and vegetative cover, and excessive fine sediments. Habitat connectivity between reaches is limited by several irrigation structures and culverts that are fish passage barriers. Riparian habitat with <60% woody vegetation on stream banks corresponds to destabilized channels and banks, high sediment supply, and elevated nutrients. Flow alterations affect the drainage, as operations of the Bitter Root Irrigation District BRID canal can greatly increase peak flows and alter frequency of critical low flows. A sediment budget indicates >2,200 tons/year of sediment production (nearly double the natural rate), primarily from eroding banks, roads, and background erosion from uplands. Gully erosion is an additional source. Nutrient concentrations are higher than other Bitterroot tributaries; key sources are sediments & livestock manure. Summer water temperatures were elevated by discharge of BRID canal water.
Based on key citizen/landowner concerns and assessment results, watershed improvement goals were developed. Priority stream reaches and upland areas were identified. Specific recommendations were developed for improvements, and for monitoring parameters and protocols to verify improvement of creek conditions. The assessment established 8 permanent monitoring reaches. Selection of reasonable indicators of project success will assure that improvement is attainable and measurable. Several pilot stream corridor projects have begun. These areas serve as demonstration sites for other landowners wanting similar work on their properties.
Start Date
1-4-2005 1:00 PM
End Date
1-4-2005 3:00 PM
Document Type
Poster
Watershed Assessment & Conservation Options for Ambrose-Three Mile Creek in the Bitterroot Basin
The State of Montana lists Ambrose-Threemile Creek of the Bitterroot River basin on its bi-annual 303(d) list as impaired by degraded water quality and aquatic habitat. A two-year watershed project assessed stream and riparian conditions and made recommendations for improvements. Work was funded by MDEQ under the 319 Non-point Source Pollution program, and many partners cooperated. The project’s purpose was to improve water quality and habitat for native aquatic life and wildlife while continuing to support agricultural uses of water. Improvements are expected to reduce nutrient and sediment loads to the Lee Metcalf National Wildlife Refuge and Bitterroot River. Project objectives were: 1) assess stream conditions; 2) develop community interest and support; 3) develop a long-term restoration program; and 4) support a stakeholder group capable of a sustained watershed restoration effort.
Three Mile Creek is a third-order stream with hydrology characterized by mean daily flows of 15-17 cfs and estimated bank-full flows of 10 cfs in Ambrose Creek, 25 cfs in upper Three Mile Creek, and 50 cfs near the outlet. Geology and soils of the watershed are important aspects of water quality problems. Land ownership is 64% private. Land cover is >55% lightly vegetated lands.
Mountain stream reaches were straighter & had lower width/depth ratios than typical. In foothills and valleys, channels were incised with vertical eroding stream banks and unstable channel forms. Stable reaches have <2% eroding banks, while reaches with disturbances have >5% and sometimes >10% eroding banks. Stream substrate in reference reaches is <45% fine material, while disturbed reaches have 55%-90%. Aquatic habitat is diminished by loss of pools, low quantities of woody debris and vegetative cover, and excessive fine sediments. Habitat connectivity between reaches is limited by several irrigation structures and culverts that are fish passage barriers. Riparian habitat with <60% woody vegetation on stream banks corresponds to destabilized channels and banks, high sediment supply, and elevated nutrients. Flow alterations affect the drainage, as operations of the Bitter Root Irrigation District BRID canal can greatly increase peak flows and alter frequency of critical low flows. A sediment budget indicates >2,200 tons/year of sediment production (nearly double the natural rate), primarily from eroding banks, roads, and background erosion from uplands. Gully erosion is an additional source. Nutrient concentrations are higher than other Bitterroot tributaries; key sources are sediments & livestock manure. Summer water temperatures were elevated by discharge of BRID canal water.
Based on key citizen/landowner concerns and assessment results, watershed improvement goals were developed. Priority stream reaches and upland areas were identified. Specific recommendations were developed for improvements, and for monitoring parameters and protocols to verify improvement of creek conditions. The assessment established 8 permanent monitoring reaches. Selection of reasonable indicators of project success will assure that improvement is attainable and measurable. Several pilot stream corridor projects have begun. These areas serve as demonstration sites for other landowners wanting similar work on their properties.