USGS Water-Year Summary 2023

10260855 Grass Valley Lake Tunnel Outlet at Lake Arrowhead, CA

LOCATION - Lat 34°15'36", long 117°12'16" referenced to North American Datum of 1983, in SW 1/4 NW 1/4 sec.16, T.2 N., R.3 W., San Bernardino County, CA, Hydrologic Unit 18090208, on left bank, 20 ft below outlet of tunnel connecting Grass Valley Lake and Lake Arrowhead, and 0.2 mi above Lake Arrowhead, in the town of Lake Arrowhead.

DRAINAGE AREA - Indeterminate.

SURFACE-WATER RECORDS

PERIOD OF RECORD - October 2008 to current year.

GAGE - Water-stage recorder, crest-stage gage, and concrete control. Elevation of gage is 5,150 ft above NGVD of 1929, from topographic map.

REMARKS - Records of daily discharge for this station represent flows leaving Grass Valley Lake by way of the east spillway. The natural flow of Grass Valley Creek, into Grass Valley Lake, is unregulated and unaffected by diversion. Lake elevations may be affected, at times, by discharges of treated domestic water and pumping for nearby irrigation. Outflow from lake is by two identical spillways. Flow over north spillway was gaged at station 10260865 (Grass Valley Creek below Grass Valley Lake, near Lake Arrowhead) but was discontinued in 2013. Flow over east spillway is gaged at station 10260855 (Grass Valley Lake Tunnel Outlet, at Lake Arrowhead), and is regulated by the spillway crest and a gated entrance to the Grass Valley Lake Tunnel, 200 ft east of the spillway. See schematic diagram of Mojave River Basin available from the California Water Science Center.

EXTREMES FOR PERIOD OF RECORD - Maximum discharge, 82.1 ft³/s, Feb. 14, 2019, gage height, 3.38 ft, from rating curve extended above 19 ft³/s, on basis of critical-depth computations; no flow for some days each year.