Stanislaus River
The Stanislaus River is a tributary of the San Joaquin River in north-central California in the United States. The main stem of the river is long, and measured to its furthest headwaters it is about long. Originating as three forks in the high Sierra Nevada, the river flows generally southwest through the agricultural San Joaquin Valley to join the San Joaquin south of Manteca, draining parts of five California counties. The Stanislaus is known for its swift rapids and scenic canyons in the upper reaches, and is heavily used for irrigation, hydroelectricity and domestic water supply.
Originally inhabited by the Miwok group of Native Americans, the Stanislaus River was explored in the early 1800s by the Spanish, who conscripted indigenous people to work in the colonial mission and presidio systems. The river is named for Estanislao, who led a native uprising in Mexican-controlled California in 1828, but was ultimately defeated on the Stanislaus River. During the California Gold Rush, the Stanislaus River was the destination of tens of thousands of gold seekers; many of them reached California via Sonora Pass, at the headwaters of the Middle Fork. Many miners and their families eventually settled along the lower Stanislaus River. The farms and ranches they established are now part of the richest agricultural region in the United States.
Early mining companies were formed to channel Stanislaus River water to the gold diggings via elaborate canal and flume systems, which directly preceded the irrigation districts formed by farmers who sought a greater degree of river control. Starting in the early 1900s, many dams were built to store and divert water; these were often paired with hydro-power systems, whose revenues covered the high cost of the water projects. In the 1970s the construction of the federal New Melones Dam incited major opposition from recreation and environmental groups, who protested the loss of one of the last free-flowing stretches of the Stanislaus. Although New Melones was eventually built, its completion is considered to have marked the end of large dam building in the United States.
Water rights along the Stanislaus River are a controversial topic, with the senior rights of farmers coming into conflict with federal and state laws protecting endangered salmon and steelhead trout. The Stanislaus irrigation districts contend that diverting water for fish damages the local economy, especially in years of drought. Water managers have struggled to find a balance between competing needs, which also include groundwater recharge, flood control, and river-based recreation such as fishing and whitewater rafting.
Course
The Stanislaus River headwaters consist of three forks in the high Sierra Nevada, in parts of Alpine County, Calaveras County and Tuolumne County. The Middle Fork, long, is the largest tributary and is sometimes considered part of the main stem. It begins in the Emigrant Wilderness of the Stanislaus National Forest about west of Sonora Pass. It flows northwest then west, receiving the Clark Fork below Dardanelle, before feeding Donnell Lake and Beardsley Lake, both formed by hydroelectric power dams. Below the Beardsley dam, it continues west to its confluence with the North Fork at Camp Nine, a popular swimming and fishing area near Hathaway Pines. The North Fork rises in the Carson-Iceberg Wilderness and flows in a generally southwest direction to its confluence with the Middle Fork, passing through several small hydropower dams. For most of their lengths, both forks flow in deep canyons through rugged, heavily forested terrain. The total length of the Stanislaus River, measured from its mouth to the head of Kennedy Creek in the Emigrant Wilderness, is about.Image:Stanislaus_River_At_Camp_9_-_panoramio.jpg|thumb|left|Stanislaus River at Camp Nine, near the confluence of the North and Middle Forks.
The confluence of the Middle and North Forks marks the start of the Stanislaus River proper. It flows southwest through a canyon to the New Melones Lake reservoir in the Sierra Nevada foothills, forming the boundary between Calaveras County and Tuolumne County. At the reservoir, it is joined by the smaller South Fork, which descends for from the Sierra Nevada to the east. Much of State Route 108 runs parallel to the South Fork, as well as the upper part of the Middle Fork, linking a number of small communities in the upper Stanislaus basin. At the lower end of New Melones Lake is the tall New Melones Dam, the sixth tallest dam in the U.S., completed in 1979 for flood control, irrigation, hydropower generation and fisheries management. Below New Melones, the river flows through the smaller Tulloch Reservoir before reaching Goodwin Dam, the oldest dam on the river where large volumes of water are diverted for irrigation.
Reduced considerably in size, the Stanislaus River leaves the foothills and enters agricultural Stanislaus County at the historic Gold Rush town of Knights Ferry. It is paralleled by State Route 120 as it flows west into the Central Valley, through Oakdale, the largest town on the river, and along the northern edge of the Modesto metro area. At Riverbank it begins to form the border of Stanislaus County and San Joaquin County. At Ripon, it is crossed by Highway 99. Below Ripon the Stanislaus flows west-southwest through a low-lying area known as River Junction and past Caswell Memorial State Park. It joins the San Joaquin River at a point about northeast of Vernalis and south of Manteca, upstream of the larger river's mouth at Suisun Bay.
Discharge
The average unimpaired runoff of the Stanislaus River, as estimated at New Melones Dam, is per year, or about. About two-thirds of the Stanislaus River flow originates as snowmelt between the months of April and July, although its highest peak flows tend to occur during winter rains. The water flow varies widely from year to year, with a historic maximum of or in the 1983 water year and a minimum of or in 1977. The highest monthly flow is typically in May or June with the peak of snowmelt, and the lowest in September or October before the arrival of autumn storms. Since the late 1800s, the timing of the spring melt has shifted two to six weeks earlier due to warming temperatures in the Sierra Nevada.Water diversions for irrigation and regulation by reservoirs have significantly lowered the mean flow of the lower Stanislaus River, smoothed out seasonal variations, and increased the dry season baseflow. The United States Geological Survey stream gage at Ripon, from the mouth, recorded an annual flow of between 1941 and 1978; after New Melones Dam was built the annual flow between 1978 and 2013 was. The highest peak before 1978 was on December 24, 1955, and the lowest monthly mean was in August 1977. After the dam was built, the highest peak was on February 28, 1997, and the lowest monthly mean was in September 2016.
Watershed
The Stanislaus River watershed drains and is divided into two distinct sections – the mountainous upper watershed, where the vast majority of its flow originates, and the narrow, heavily developed lower watershed where it flows across the San Joaquin Valley. Goodwin Dam has traditionally been considered the dividing line between the upper and lower watersheds. Elevations in the watershed range from less than at the confluence with the San Joaquin River to over in the high Sierra Nevada. Annual precipitation varies from in the valley regions to or more at higher elevations; at elevations above most precipitation falls as snow.The upper watershed comprises 90 percent of the total area and supplies a commensurate proportion of the river flow. Stretching from the foothill to alpine regions of the Sierra Nevada, it consists of rugged narrow canyons and ridges with an average local relief of or more from river to rim. Much of the watershed is at high elevation, with 40 percent of the total area above winter snow line. The average precipitation in the upper basin as a whole is. The vast majority of the upper basin is either undeveloped or commercial timber land, with very small areas of agriculture, ranching, and mountain meadows above the tree line. The higher elevations are mostly federal Forest Service land and designated wilderness, while the middle elevations are a patchwork of state, federal and privately owned land. Much of the private timber land has been subject to checker-board clearcutting, which has greatly fragmented wildlife habitat.
The lower Stanislaus River watershed comprises only about one-tenth of the total area and is used mainly for agriculture and urban development, with minimal open space. Major communities near the lower river include Copperopolis, Knights Ferry, East Oakdale, Oakdale, Riverbank, Escalon, Salida and Ripon. The long lower river has been modified extensively not only by water diversions, but by channelization and levee construction to drain wetlands and prevent floods. Most of the natural floodplain no longer exists, and about half of the former riparian habitat has been lost. The river bed has been subjected to extensive gravel mining, with an estimated 6.3 million yd3 extracted between 1939 and 1999.
Geology
The Stanislaus River is believed to have originally formed sometime during the Miocene period, about 23 million years ago, flowing down from an ancient mountain range in the current location of the Sierra Nevada that has since eroded away. Huge lava flows moved down the ancestral canyon, filling it with volcanic rock and sediment. About 9 million years ago during the Pliocene, the most recent period of orogeny occurred, tilting the predominantly granitic Sierra Nevada batholith to form a regional slope to the west. As the mountains rose the Stanislaus River established its modern course, carrying away the volcanic material that had filled the ancestral canyon. This orogeny coincided with a second period of volcanic activity, during which lava flows displaced the Stanislaus River course several times where it flows through the foothills, causing it to carve new canyons through underlying sedimentary rock. The lava flows are today known as the Stanislaus Formation, and are most visible as the caprock layer of the distinctive "table mountains" around present day New Melones Lake.Image:Donnell_Lake.JPG|thumb|left|The Stanislaus River canyon at the Dardanelles area, where Donnells Lake reservoir is today, was formed by glaciation during the Ice Ages.
As both uplift and erosion continued, the Stanislaus River gradually carved the rugged canyons it flows through today, and contributed to the vast alluvial deposits that make up the flat floor of the Central Valley. Some of these fluvial sediments, originating from gold-bearing veins in the granite batholith, were deposited as placer gold in the river bed to be discovered later during the California Gold Rush. The lower course of the river is geologically young, dating to no earlier than the Holocene; the river has continually cut new channels through its sediments and filled in older ones, creating a sequence of river terraces.
Most of the erosion that shaped the modern Stanislaus River basin is believed to have occurred during glacial and interglacial periods in the Pleistocene, starting about 1 million years ago. During the ice ages California had a much wetter climate; average river flows in the past may have been as high as what is considered "flood stage" today. The climate was also cold enough to support large glaciers in the Sierra Nevada at elevations above. These glaciers carved large U-shaped valleys in the high elevations, and supplied vast volumes of meltwater which accelerated erosion along the foothill canyons of the Stanislaus River. During the last glacial period the main Stanislaus glacier was up to long; during previous ice ages it may have extended as far as. Although glaciation did not have as dramatic an impact on the Stanislaus River watershed as it did further south, many major features of the upper Stanislaus were sculpted by ice, such as the Clark Fork valley and the Middle Fork valley at Donnell Lake.