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Section 4 – Surface and Groundwater HydrologyIntroductionThe Upper San Joaquin River sustains the only perennial flow within the Millerton area watershed. All creeks and streams including the three major watersheds: Cottonwood, Finegold and Big Sandy are classified as seasonal or intermittent. These streams usually are dry by June – and only begin to flow after the first significant rains occur late in the year. Soils and decomposed organic materials may be rather thin or non-existent in general. The surfaces may be hard and compacted. As noted earlier, the Millerton area watershed is situated in the lower foothills portion of the Sierran granitic batholith. Fractures of varied uniformity are prevalent throughout this formation. These fractures are greater in size and number closer to the surface. Deeper away from the surface there is less spacing and fewer fractures in which water may be stored. The hydrological interrelationship between seasonal surface runoff and the recharging fractured rock ground water sources may be generally understood. The Todd Engineer Technical Memorandum draft submittal to Madera County in March, 2003 makes an effort to estimate what the effectiveness of ground water recharge capabilities in a fractured rock formation. EvapotranspirationEvapotranspiration (ET) is a term to describe the quantity of water transpired (given off) and evaporated from plant tissues and surrounding soil surfaces.[1] Reference Evapotranspiration (ETo) is a term used to describe the Evapotranspiration rate of a reference crop in either inches or millimeters.[2] The Millerton area watershed lies within the Evapotranspiration (ETo) Zones 12 and 14. ETo Zone 12 is known as Eastside Sacramento-San Joaquin Valley and ETo Zone 14 is known as the Mid-Central Valley, Southern Sierra Nevada, Tehachapi and High Desert Mountains. According to the Todd Engineer draft Technical Memorandum, annual Evaporative Demand exceeds precipitation throughout all of the lower foothills and thus the Millerton Watershed. For example, Evaporative Demand exceeds 60 inches in the Millerton Lake area – and the amount of Annual Mean Precipitation at Friant Government Center is 13.4 inches. Likewise the Evaporative Demand continues at 60 towards the farthest extents of the watershed at Auberry with an Annual Mean Precipitation of 24.83 inches and North Fork (Ranger Station) – with an Annual Mean Precipitation of 33.45 inches. All existing information on the
surface and groundwater hydrology, and ETo values within the Millerton Area
Watershed appears to apply to the Upper Finegold Watershed. The headwaters of
the Upper Finegold appear to lie within Zone 14.
Figure SEQ Figure \* ARABIC 38 – Reference Evapotranspiration (ETo) map of California and watershed location
PercolationAccording to the Todd Engineers Technical Memorandum, estimating groundwater recharge is key in determining the perennial water yield from a drainage basin. Based on modeling analyses and DWR estimates, a representative and conservative value for net groundwater recharge is approximately 10 percent of precipitation.[3] Water for percolation or recharging is affected by the slope conditions, geological structure, soils composition, evapotranspiration rate and other influences. The following table summarizes the results of Todd Engineer’s analysis for the Oakhurst and Raymond areas of eastern Madera County. Table SEQ Table \* ARABIC 11 – Ground Water Recharge Analysis of Oakhurst and Raymond, Madera County
Impervious SurfacesAccording to information noted in the multi-agency Working at a Watershed Level publication, research has shown that streams in urban watersheds have a character fundamentally different from that of streams in forested, rural, or even agricultural watersheds. The amount of impervious cover in the watershed can be used as an indicator to predict how severe these differences can be. In many regions of the country, as little as 10 percent watershed impervious cover has been linked to stream degradation, with the degradation becoming more severe as the impervious cover increases (Schueler 1995). Since impervious cover prevents rainfall from infiltrating into the soil, less flow is available to recharge ground water (Simmons and Reynolds 1982).[4] It is unknown if there has been
research regarding impervious surfaces and what role this 10% sensitivity
threshold may have within relatively developed areas of the Millerton
watershed. The Todd Engineers report did not cover this as a part of their
study. Upper Finegold Surface and Groundwater Hydrological Analysis under Phase 2The underlying hydrological relationship of surface water and groundwater is not well known within the Upper Finegold Watershed. Initial efforts to collect data relevant to understanding this relationship has just recently been initiated, under Phase 3. Well log information established within the Department of Water Resources (DWR) relational database – and initial spatial analysis of the data that was performed by the California Water Institute-CSUF constitutes the first meaningful effort to analyze this relationship within the Upper Finegold. As noted previously the underlying geology of the Upper Finegold Watershed is predominately granitic (21,539 acres – 71%) with variations in fracture length, depth and widths. These fractures are non-uniform in nature. Within the headwater and higher elevations of the watershed the geology also consists of meta-sedimentary and meta-volcanic materials (6,190 acres – 29%).
[1] California Water Plan – Bulletin 160-93, pp. 16, 1993 [2] CA Department of Water Resources, California Irrigation Management Information System (CIMIS) [3] Todd Engineers Technical Memorandum to Madera County, pages 24 and 25. See Appendices for table [4] Working at a Watershed Level, pages 3-23 to 3-25
Figure SEQ Figure \* ARABIC 39 - Geology of the Upper Finegold Watershed
Summary of Findings – Phase 11. There is an important relationship between surface and groundwater hydrology within the watershed. The Todd Engineers Technical Memorandum Groundwater Conditions (of) Eastern Madera County provides for a general understanding of that relationship. 2. Outside of the San Joaquin River, the majority of the watershed’s drainage is primarily ephemeral streams that flow for a few days after a storm event. 3. Much of the year, (approximately June through October) there is very little precipitation – and no surface run-off or stream flows. 4. According to USDA Soils Survey information, soils for moisture retention and percolation appear to be thin and not widely distributed within the Millerton area watershed. 5. Evaporative Demand significantly exceeds the amount of precipitation available within the watershed by a factor of approximately five to one (5:1) to at best a little less than two to one (2:1) in the uppermost portions of the Millerton Watershed. 6. According to the Todd Engineers Technical Memorandum, percolation or ground water recharge for eastern Madera County is conservatively estimated to be approximately ten percent (10%) of precipitation. 7. It is not known what if any role impervious surfaces due to land use or development activities contribute to the alteration of run-off or percolation.
Summary of Findings for Upper Finegold Watershed based upon field monitoring and surveys – Phase 21. Phase 1 findings continue to be relevant to the Upper Finegold Watershed. 2. The Upper Finegold appears not to have had any investigations subsequent to the publishing of the Phase 1 report in February, 2004. 3. The dominate geology of the Upper Finegold is composed of Mesozoic granitic rocks. 4. Large areas of impervious surfaces were not observed within the Upper Finegold Watershed during field surveys conducted for other resource investigations.
Conclusions – Phase 11. There are no known field studies conducted within the Millerton area watershed to ascertain what the probable percolation or recharge rate(s) may be. 2. There are no known field studies conducted within the Millerton area watershed to ascertain what the discharge or depletion rate may be for the watershed. 3. There are no known field studies conducted within the Millerton area watershed to ascertain the age of groundwater – and whether “mining” without recharge is occurring. 4. There are no known field studies conducted within the Millerton area watershed to determine what role that surface soils, their composition and condition may contribute towards moisture retention and percolation. 5. There are no known field studies conducted within the Millerton area watershed to determine what role that vegetation contributes or detracts from moisture retention and percolation. 6. There are no known field studies conducted within the Millerton area watershed to ascertain what role – if any impervious surfaces impact ground water recharge in development clusters.
Conclusions – Upper Finegold Phase 21. Phase 1 conclusions continue to be generally relevant to the Upper Finegold Watershed. 2. The California Department of Water Resources re-analysis of the water budget within the DAU (Detailed Analysis Unit) 203 articulates the overall impact to a watershed such as the Upper Finegold Watershed in which there is an extraction of groundwater, (see Section 2).
Go to Section 5
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