Mono Basin Clearinghouse
Real-time Data Companion Page: 
Explanations and additional resources.

EXPLANATIONS:
(counter-clockwise on map)

MONO LAKE ELEVATION
The date when it was read is not shown (it is not real-time), and the reading (as of 10/19/09) is incorrect or old. LADWP's datum is 0.37 feet lower than the USGS datum used by the SWRCB. The correct recent level can be found on the Mono Lake Website. The transition to 6,391 feet asl is expected to take until 2021 with average past climate.

LEE VINING CREEK
Second largest creek in the Mono Basin. More background here. "Above" the diversion is controlled mostly by what SCE releases from upstream reservoirs. This year, April 1 through September 30 minimum flow "below" is 54 cfs (or "above" flow, whichever is less), and October 1 through March 31 minimum flow is 40 cfs (or "above" flow). The SWRCB approved a temporary change until March 31, 2010 allowing the flow to be as low as 16 cfs in 2009 and 12 cfs in 2010. In Normal years Stream Restoration Flows are required--the peak flow must pass undiverted downstream. Note: The flows below are sometimes incorrect, but can sometimes be calculated by subtracting "conduit" from "above".

AQUEDUCT CONDUIT
This is the route by which water is diverted to Grant Lake Reservoir from Lee Vining, Walker, and Parker Creeks. Diversions are not allowed when the creeks are below their minimum flows. Augmentation of Rush Creek SRFs with Lee Vining Creek water is only allowed when runoff is greater than 107% of average (up to 50 cfs in Wet-Normal years, 100 cfs in Wet, and 150 cfs in Extreme Wet years) and 7 days after Lee Vining Creek peaks. In Extreme Wet and Wet years augmentation is allowed for a maximum of 15 days, in Wet/Normal years a maximum of 5 days.

WALKER CREEK
Smallest of the four diverted streams. More background here. In all years, April 1 through September 30 minimum flow "below" is 6.0 cfs (or "above" flow), and October 1 through March 31 minimum flow is 4.5 cfs (or "above" flow). Flow through conditions are required during Rush Creek Stream Restoration Flows and anticipated Walker Creek SRFs. There are no plans to divert Walker Creek until the diversion facility is upgraded. In 2009 a sediment bypass procedure was tested that drained the ponds at the diversion dams during the peak flow.

PARKER CREEK
Second smallest of the four diverted streams. More background here. In all years, April 1 through September 30 minimum flow "below" is 9.0 cfs (or "above" flow), and October 1 through March 31 minimum flow is 6.0 cfs (or "above" flow). Flow through conditions are required during Rush Creek Stream Restoration Flows and anticipated Parker Creek SRFs. There are no plans to divert Parker Creek until the diversion facility is upgraded. In 2009 a sediment bypass procedure was tested that drained the ponds at the diversion dams during the peak flow.

GRANT SPILL
The only time this will show a flow is when Grant Lake Reservoir is spilling (at or above 7130.0 elevation). The reservoir is not expected to spill in 2009.

RUSH CREEK
Largest creek in the Mono Basin. This is the flow "at damsite," or what is coming into Grant Reservoir. It is usually controlled by SCE's releases from upstream reservoirs. In most years SCE must maintain its reservoirs near spill from July 1 to September 1, causing low flows during the spring, and relatively high flows in the fall when the reservoirs are drained. In 2009 Rush Creek Meadows (Waugh Reservoir) will remain empty (due to dam maintenance) resulting in less deviation from the natural hydrograph at this location. More background here.

GRANT LAKE RES. ELEVATION
The "full" level of the reservoir is 7130.0 feet, equivalent to 47,171 acre-feet of storage. DWP is required to seek to keep Grant between 30,000 (7113.2') and 35,000 acre-feet (7118.4') on April 1, and above 40,000 acre-feet (7123.4') in wet years. Below 26,200 acre-feet (7108.9') the marina has difficulty operating (no safe harbor), and below 22,800 acre-feet (7105') the boat ramp is out of the water and warm water releases become a problem. Below 15,000 acre-feet (7094.5') high levels of turbidity are released from the reservoir that violate water quality rules, and dust storms rise from the back bay. DWP is never required to reduce storage below 11,500 acre-feet (7089.3'), although below this level the inflow must be passed downstream or the dry year minimum, whichever is less. In 2009 the reservoir was projected to drop below 11,500 ac-ft, and the Water Board issued an opinion that no Stream Restoration Flows are required in Rush Creek this year in order to increase storage. Click here to see Grant Lake Res. storage at the end of the previous month.

GRANT LAKE RES. OUTFLOW
The outflow is equal to the "Rush Creek Return Ditch" plus "West Portal". Problems with this gauge in 2008 seem to have cleared up.

RUSH CREEK RETURN DITCH
This ditch is the only reliable route through which a controlled release of water can be sent down Rush Creek. It was upgraded in 2003 to carry a maximum capacity of 380 cfs. In prior years the low capacity limited Stream Restoration Flows (SRF) and Channel Maintenance and Flushing Flows (CMF) below those ordered by the Water Board. This year Mono Gate One at the head of the ditch is being rebuilt so that flows above 350 cfs can be safely delivered. This year, April 1 through September 30 minimum flow is 47 cfs, and October 1 through March 31 minimum flow is 44 cfs. The SWRCB approved a temporary change until March 31, 2010 that allows flows as low as 28 cfs. If the inflow is less than this, minimum flow is inflow, and minimum (Oct-Mar) is 36 cfs when inflow is less than 36 cfs. In 2009, an SRF of 380 cfs for 5 days followed by 300 cfs for 7 days would be required but has been waived by the Water Board. DWP is not required to release water in an SRF if it projects that it would cause the reservoir to drop below 11,500 acre-feet by the end of the runoff year (as has been projected this year). In Normal Years a Channel Maintenance and Flushing Flow of 200 cfs for 5 days is required by D1631, and delivering it would not cause the reservoir to drop below 11,500 ac-ft. There are differing legal opinions about whether this is required this year, despite language in Order 98-05 that says "This order refers to the flows above as "Stream Restoration Flows" (SRFs) in order to distinguish between the flows required for stream restoration under this order and the Channel Maintenance Flows required by Decision 1631. ...The SRFs specified in this order are minimum flows and are in addition to the flow requirements set forth in Decision 1631." It was not delivered because the legal confusion was not resolved in time.

WEST PORTAL
West Portal flow is what is flowing from Grant Lake Res. into the Mono Craters Tunnel. East Portal, the outlet of the tunnel at the Upper Owens River, will usually be about 15 cfs higher due to groundwater seepage. The amount of annual surface water export is limited by Mono Lake level and minimum flows (not by SRFs). This year, 16,000 acre-feet of export is allowed, and flow will resume after Mono Gate One construction ends at the end of October. Note: this flow is sometimes incorrect. To check this number, subtract "Rush Creek Return Ditch" from "Grant Lake Res. Outflow".

Explanation provided by the Mono Lake Committee. Last updated 10/19/09.