Restoring River Substrate Using Instream Flows: The Gunnison and Trinity Rivers

The Gunnison and Trinity Rivers are two western rivers with major reservoirs were downstream aquatic habitat must be relatively free of sediment. The Gunnison River is a gravel bed river with large loads of fine material. The discharge needed to maintain the river in the condition needed by Colorado squawfish varies from 210 to 484 cubic meters per second (cms) depending on the objective. The overall objectives will be met if the discharge exceeds 484 cms one in every three years, with one in every two years having a discharge of at least 354 cms, and two in every three years having a discharge of 354 cms for at least four days. The Trinity River has a gravel bed and the river transports large quantities of sand; fines (material ≤ 0.062 mm) are relatively unimportant. The Trinity River is spawning and rearing habitat for Chinook salmon. The streamflow required to flush sediment from the substrate is 190 cms. The discharge needed to transport sediment size which should be transported and not allowed to deposit on the stream bed (1 mm or smaller) is 70 cms. This discharge is required only when Grass Valley Creek (a tributary moving large quantities of sand) is transporting sediment to the Trinity River.