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Technical Information

Annual Reports


Reports are generally available for inspection at Watermaster offices during business hours. Some are available for purchase. Please call for further information. 

WEB ALL 2023 WM flush book  10_31_23 1.jpg
WEB ALL 2023 WM 5 year 11_1_23 1.jpg
OSYRPT Preliminary_24-25 1.jpg
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Operating Safe Yield

Watermaster Rules and Regulations state: "Watermaster shall annually determine the Operating Safe Yield applicable to the succeeding Fiscal Year and estimate the same for the next succeeding four (4) Fiscal Years. Said determination shall be made at the close of the hearing thereon, which shall be commenced at Watermaster's regular meeting in May of each year..."

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Groundwater Level Contour Maps


11x17" color, downloadable PDF. Earlier dates can be made available upon request.

Simulated 2018-19 Groundwater Contours (see: Five Year Plan)

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Salt and Nutrient Management Plan-Draft Update

February 2016, an updated draft of the San Gabriel Basin Salt and Nutrient Management Plan (SNMP) was made available for review.

(From the Executive Summary) 
"The State Water Resources Control Board approved Resolution No. 2009-0011 to adopt the Recycled Water Policy in February 2009. Included in that resolution is a requirement for a Salt and Nutrient Management Plan (SNMP) to be prepared for all groundwater basins. The Main San Gabriel Basin Watermaster is the lead agency for the preparation of the San Gabriel Basin SNMP. The primary stakeholders include Upper San Gabriel Valley Municipal Water District, San Gabriel Valley Municipal Water District, Three Valleys Municipal Water District, the Metropolitan Water District of Southern California, the Los Angeles County Sanitation Districts, and the Los Angeles County Department of Public Works.

The SNMP reviewed the geology, hydrology and hydrogeology of the San Gabriel Basin, along with the institutional and management structure for the San Gabriel Basin. TDS, Nitrate, Sulfate, and Chloride were identified as the primary constituents of concern. Sources of loading (precipitation, subsurface inflow, infiltration of applied water, storm runoff and untreated imported water replenishment) and unloading (groundwater pumping and subsurface outflow) were included in a spreadsheet computer model, along with average water quality data for TDS, Nitrate, Sulfate, and Chloride, on an annual basis. Watermaster developed this spreadsheet model as a tool to calculate the impacts of loading and unloading from numerous water supply components

Download the full Salt and Nutrient Management Plan (SNMP) here.

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