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Title: BED-MATERIAL CHARACTERISTICS OF THE SAN JUAN RIVER AND SELECTED TRIBUTARIES, NEW MEXICO: DEVELOPING PROTOCLS FOR STREAM-BOTTOM DEPOSITS

Author
item HEINS, AMANDA - UNIV. OF NOTTINGHAM
item Simon, Andrew
item FARRUGIA, LAUREN - UNIV. OF MISSISSIPPI
item FINDEISEN, MICAH - UNIV. OF MISSISSIPPI

Submitted to: Laboratory Publication
Publication Type: Government Publication
Publication Acceptance Date: 8/30/2004
Publication Date: 8/30/2004
Citation: Heins, A., Simon, A., Farrugia, L., Findeisen, M. 2004. Bed-material characteristics of the San Juan River and selected tributaries, New Mexico: developing protocls for stream-bottom deposits. USDA-ARS National Sedimentation Laboratory Research Report. No. 47. 62 pp.

Interpretive Summary: Deposition of excessive fine sediment in coarse-bed river channels impacts habitat conditions for fish and macroinvertebrates. The purpose of this investigation was to develop a bed-sediment protocol for discriminating between natural and impacted conditions, based on data from the San Juan River between Navajo Dam and the Navajo Nation Boundary, and Animas Rivers between the New Mexico/Colorado border and its confluence with the San Juan River. A similar analysis was carried out at river gaging station locations in the Arizona/New Mexico Plateau Ecoregion (Ecoregion 22), containing most of the study area. Field work involved geomorphic assessment and collection of bed material at study sites on the Jan Juan and Animas Rivers. Additional sites were added around the mouths of major tributaries. The long profile of percent of bed-material sand and finer showed extremely high values at and downstream of the mouth of Canon Largo. This was interpreted as a large contribution of fine sediment from this source. Other peaks in bed-material percent fines were observed near confluences of Gallegos and Kutz Canyons and La Plata River on the San Juan, and Estes Arroyo on the Animas River, indicating these also contribute fines. The bed material reference value, defined as the median percentage of material finer than 2 mm for stable coarse-bed channels on the San Juan and Animas River is 20.5%; this value is slightly higher than those for the Ecoregion 22 dataset. 15.5%.

Technical Abstract: The purpose of this investigation was to develop a bed-sediment protocol for discriminating between natural and impacted conditions, based on five designated reaches of the San Juan and Animas Rivers, listed as impaired on the New Mexico 303-d list. A similar analysis was carried out using sixty-five selected gauging stations in the Arizona/New Mexico Plateau Ecoregion (Level III Ecoregion 22), containing the study reaches. Rapid geomorphic assessments and collection of bed-material samples were carried out at 1.5 km intervals over the 110 km length of the San Juan River, at 3 km intervals on the 55 km length of Animas River and near the mouths of major tributaries. The long profile of percent bed-material finer than 2 mm exhibited extremely high values at and downstream of the mouth of Canon Largo. This was interpreted as a large contribution of fine sediment from this source. Other peaks in bed-material percent fines were observed near confluences of Gallegos Canyon, Kutz Canyon, and La Plata River on the San Juan, and Estes Arroyo o n the Animas River, indicating these are also contributors of fine sediment. Hydrological analyses of gauging station data on the San Juan River showed following dam construction in 1962, peak flows had decreases significantly in terms of magnitude and duration. This resulted in reduced sediment-transport capacity, especially in the reach downstream of Canon Largo. The bed material reference value, defined as the median percentage of material finer than 2 mm for stable coarse-bed channels on the San Juan and Animas River is 20.5%, with the interquartile range extending between 12.8% and 29.5%. These values are slightly higher than those for the Ecoregion 22 dataset, being 0.25%, 15.5%, and 21.5%, for the 25th, 50th, and 75th percentiles, respectively.