Three Rivers Water Supply Study analyzes area usage

 

Integrated Regional Water Management (IRWM)— IRWM is a collaborative, cross-jurisdictional, and multi-benefit process for managing water. It works off the premise that outcomes are more sustainable when people from a diversity of viewpoints agree on solutions, when participants maximize multiple benefits, and when planning efforts transcend federal, state, county, and local jurisdictions. At a time when economic and human capacities are stretched thin, collaboration expands a region’s collective resources to address local and regional issues.

 

Southern Sierra Region Water Management Group (RWMG)— The RWMG, formed in 2008, is recognized by DWR as the Integrated Regional Water Management (IRWM) group for the southern Sierra region. The RWMG is a voluntary collaboration of nonprofit organizations, agencies, local water/flood/conservation districts, and landowners. Its mission is to provide a forum to discuss, plan, and implement creative, collaborative, regional, integrated water/natural resource/watershed management actions that enhance the natural resources and human communities of the southern Sierra region. For the past six years, the group has convened public meetings to plan and implement creative water management solutions that enhance the natural resources and human communities in the expansive region. 

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With the impacts of drought gripping California for the third year, information about water is more important than ever. At the Three Rivers Town Hall meeting on Monday, Nov. 3, I provided an overview of the Southern Sierra Regional Water Management Group and its recently released water management plan, while California Department of Water Resources (DWR) engineering geologist John Kirk informed attendees of the Three Rivers Water Supply Study, one of two projects currently being implemented by the RWMG. 

As Three Rivers residents know, the southern Sierra is one of the more severely drought-impacted areas of California and is critically important to southern San Joaquin Valley residents and beyond. The region includes many of California’s most precious natural resources: Sequoia and Kings National Parks; Sequoia, Sierra, and Inyo national forests; Devils Postpile National Monument; and the upper watersheds of the Kaweah, Kings, Kern, Tule, San Joaquin, Deer, and White rivers, in addition to several smaller watersheds.  

Southern Sierra Integrated Regional Water Management Plan— The RWMG recently released its Southern Sierra Integrated Regional Water Management Plan, a voluntary, non-regulatory planning document that identifies consensus-based, multiple-benefit water resource projects and programs for the 6,200-square-mile region. Examples of multiple-benefit projects and programs include those that improve water quality, provide better flood management, restore and enhance ecosystems, and create more reliable water supplies. Such multiple-benefit projects are the best shot at managing California’s erratic precipitation patterns in the face of increasing water demands and a changing climate. 

Three Rivers Water Supply Study— The RWMG recently sponsored and received funding for two projects: the Long Meadow Restoration Project (Kern River watershed in Sequoia National Forest) and the Three Rivers Water Supply Study. 

In 2009, the RWMG identified a critical need for better information about groundwater in the southern Sierra. We worked with consultants to determine the scope of work and cost for water supply studies in at least five southern Sierra communities and, in 2012, I wrote a water supply study prospectus based on discussions with DWR and input from the region’s stakeholders. In 2013, DWR’s Fresno office agreed to support a pilot water supply study, selecting Three Rivers because of its central location and community interest in learning about the local and regional water supply. 

The study seeks to understand the “water budget,” or quantity and quality of the water in the Kaweah watershed as it flows from the Great Western Divide and nine smaller watersheds and into the underground aquifer. The study examines several aspects of the area: local geography, geology, land use, precipitation, hydrographs, and water demand. Geology plays an important role in water quantity and quality because much of the area’s water comes from water stored in the fractures and fissures of the hardrock aquifer. 

Precipitation is an obviously important factor in the water balance because of the snowpack that accumulates in the upper watersheds and the need for rain and snowfall to replenish river and groundwater levels. The study examined the logs for 500 wells (about half of the wells in the area), which offer valuable information about the geology where the wells are drilled and the water quality and quantity in the well. 

Three Rivers study findings— The study also examines water demand and compares it to water availability at different times of year. The study identified that 54 percent of the land in the watersheds were in public ownership (National Parks and Bureau of Land Management), while 46 percent were privately owned. 

The study area has a total of 1,575 parcels, 81 percent of which are smaller than 10 acres and located primarily along Kaweah River tributaries. 

The water flow along the Kaweah River in Three Rivers is subjected to dramatic increases in March through June when abundant water flows from snowmelt  and swells rivers and fills underground rock fractures. 

The average precipitation in the Kaweah watershed ranges from over 55 inches at the crest of the Great Western Divide to a low of 14 inches at the base of the local watershed near Lake Kaweah with an average of 22 inches for the whole watershed. 

The study estimates that the watershed recharges approximately an average of 4 inches of that 22 inches of average precipitation across the watershed and that Three Rivers residents collectively use over 300 acre-feet of groundwater each year. 

With a population of more than 2,000 residents and approximately 1,000 households, annual use in Three Rivers is estimated to be 110,000 gallons (0.34 acre-feet) per resident. Three Rivers residents use 200 gallons per day in the winter and nearly 500 gallons each day in the summer. 

Unfortunately, this greatest water demand occurs when the quantity of water in the river and in groundwater is lowest. In other words, demand is highest when supply is lowest. 

In Three Rivers, 10 percent of wells surveyed were less than 50 feet, 22 percent had depths of less than 100 feet, but the majority of wells (68 percent) were between 100 and 500 feet. Half of wells had yields greater than 15 gallons per minute, 42 percent of the wells had yields between 2 and 15 gpm, and 8 percent of the wells yield less than 2 gpm. Interestingly, very few dry wells are reported from the watersheds around Three Rivers while hundreds of wells are dry in the Valley this year.  

Water quality in the Kaweah watershed is best at the highest elevations where precipitation is greatest and recharge exceeds water demand, however, few people li
ve there. In and around Three Rivers, a number of wells have poor water quality, including high salt content (exceeding drinking water standards), sulfur, hydrogen sulfide, or bacteria. 

Pilot water study— The information in the study is included in the IRWM plan and provides a pilot for other communities in the southern Sierra who wish to better understand their water supply. In the future, the area will need to plan land use and development patterns carefully so as not to negatively impact the water supply. 

This study comes at an important time when a long-term drought is causing everyone to rethink water use and as the Three Rivers Community Plan Update nears completion. 

Three Rivers residents cannot take water availability for granted nor assume that there will always be abundant supplies or good quality in the future. It is imperative that the community learns to plan carefully and conserve this precious resource. 

Learn more about the Southern Sierra IRWM region and the Three Rivers Water Supply Study at www.southernsierrarwmg.org.

Bobby Kamansky of Three Rivers is a biologist and owner of Kamansky’s Ecological Consulting with over 15 years of biological and ecological experience.

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