The five principal creeks, First Creek, Second Creek, Wood Creek, Third Creek, and Incline Creek, with a cumulative drainage of 17.8 square miles, furnished a yearly average of about 15,000 acre-feet of runoff, mainly snowmelt, to Lake Tahoe during the 1970-73 water years. Annual runoff from the individual streams ranged from 460 to 7,070 acre-feet, and discharges ranged from 0.2 to 110 cubic feet per second. During the 4 years, the five streams delivered 31,000 tons of sediment, which averaged about 75 percent gravel and sand, 15 percent silt, and 10 percent clay, to the lake. Annual quantities ranged from 1,500 to 11,000 tons; individual streams furnished 20 to 5,200 tons annually. Measured sediment transport at the stream mouths ranged from 1 to 13,200 milligrams per liter and from 0.001 to 1,420 tons per day; sediment concentrations up to 63,200 milligrams per liter were measured at upstream tributary sites.
Estimated annual sediment yields of principal drainage basins ranged from 3 to 930 tons per square mile from undeveloped areas and from 26 to 5,000 tons per square mile from developed areas; yields for developed areas appeared to average about 10 times those of undeveloped areas, and roadways apparently were the major source. Erosion disequilibrium caused by prestudy flash floods on two creeks continues to manifest itself through high natural sediment yields. The Second Creek flood of 1967 yielded about 75,000 tons in one afternoon.
Fluvial nutrient transport seems quantitatively related to magnitudes of sediment and water transport. Movement rates of organic nitrogen and particulate phosphorus were greater than rates of other nutrient species moving to the lake.
