Pit River
The Pit River is a major river draining from northeastern California into the state's Central Valley. The Pit, the Klamath and the Columbia are the only three rivers in the U.S. that cross the Cascade Range.
The longest tributary of the Sacramento River, it contributes as much as eighty percent of their combined water volume into the Shasta Lake reservoir; the junction of their Shasta Lake arms is northeast of Shasta Dam. The main stem of the Pit River is long, and some water in the system flows to the Sacramento River measuring from the Pit River's longest source.
The Pit River drains a sparsely populated volcanic highlands area in Modoc County's Warner Mountains, passing through the south end of the Cascade Range in a deep canyon northeast of Redding. The river is so named because of the semi-subterranean permanent winter homes and large 'sweat houses' that the Pit River Tribe dug, and their pit traps for game that came to water at the river.
The river is a popular destination for fishing, fly fishing, and rafting in its lower reaches, and is used to generate hydroelectricity in the powerhouses below Fall River Mills where the Pit and Fall rivers join, and at Shasta Dam. It is also used extensively for irrigation and conservation purposes.
Course
The Pit River rises in several forks in Modoc, Lassen and Shasta counties in the northeastern corner of California. The South Fork Pit River - West Valley Creek - Cedar Creek source originates just southeast of Buck Mountain in the Warner Mountains, in the extreme southeastern corner of the Modoc National Forest west of the California–Nevada border. The South Fork is formed from the confluence of several creeks in Jess Valley northeast of Madeline and flows west through a narrow canyon, past Likely, then generally north through a broad ranching valley where its waters are diverted for irrigation and waterfowl conservation via an extensive system of canals.The long North Fork - Linnville Creek tributary begins southeast of the town of Davis Creek, near Goose Lake. It flows generally south-southwest, joining the South Fork from the north near Alturas. Although Goose Lake is generally considered the terminal sink of an endorheic basin, it will overflow into the Pit River during floods; however this has not occurred since 1881 due to large diversions of water for agriculture.
The combined river flows west-southwest in a winding course across Modoc County, past Canby and through the Modoc National Forest in the narrow Stonecoal Valley Gorge. It turns south to flow past Lookout and into northern Lassen County, past Bieber, to emerge into the ranching region of Big Valley. North of Little Valley it flows into northeast Shasta County and the Shasta National Forest. Then the river reaches Fall River Valley, where it is joined by the Fall River, which is fed by one of the largest freshwater spring systems in the United States. After passing through the town of Fall River Mills, the river drops over Pit River Falls, then enters the head of a long serpentine canyon that cuts through the southern Cascade Range. It then turns south to join the Sacramento River as the eastern arm of Shasta Lake reservoir, approximately north of Redding. Potem Creek joins the river at Potem Falls. Two major tributaries, Sulanharas Creek and the McCloud River, join the Pit from the north within the lake. The lower of the river forms the longest of the five arms of Shasta Lake, which is formed by Shasta Dam on the Sacramento downstream from the original confluence.
Hydrology
Fed by significant volcanic groundwater basins that produce some of the largest contiguous freshwater spring systems in the United States, the middle and lower reaches of the Pit River exhibit a strong year-round flow, in contrast to the highly seasonal nature of most northern California rivers. Before Shasta Dam was built, the Pit contributed as much as 85 percent of the Sacramento River's dry-season flow as measured at Red Bluff, nearly downstream of their confluence – making the river an important resource for irrigation, and later, hydroelectricity. The upper reaches of the Pit above Fall River Mills are a snow-fed high desert stream with a much more seasonal hydrograph. The lowermost part of the Pit River system receives heavy winter rainfall, which mainly contributes to streamflow between November and April. Nevertheless, summer low water flows rarely drop below.While conducting surveys for irrigation projects in the early 1900s, the U.S. Reclamation Service noted that the spring-fed Fall River alone contributed a year-round flow of about, from an aquifer fed in part by Mount Shasta snowmelt. Much of this water rises at what is often called "Thousand Springs" a few miles above Fall River Mills, west of Ahjumawi Lava Springs State Park. Hat Creek and Burney Creek, spring-fed from the Lassen Peak area, supplied a further to the Pit River. The aquifers in the Pit River basin may hold as much as in storage and are consistently replenished by winter precipitation seeping through the watershed's porous volcanic rocks and soils. The water typically emerges at points of lower elevation where the surface layers encounter harder metamorphic and sedimentary rock.
Image:Pit River Valley.jpg|thumb|left|The Pit River before it enters the canyons west of Canby, Modoc County
The U.S. Geological Survey operates a stream gage on the Pit River at Montgomery Creek, directly below Pit 7 Dam and above Shasta Lake. This gage measures streamflow from an area of, or 70 percent of the total watershed. The average streamflow between 1966 and 2012 was, with a maximum of recorded on January 24, 1970, after heavy rainfall. A short minimum flow of occurred on July 12, 1975 due to construction work at Pit 7 Powerhouse requiring temporary cessation of releases. The minimum 7-day flow was, on September 5–12, 1966.
Before the damming of Shasta Lake in the 1940s, the annual flow of the Pit River was about four times the size of the Sacramento at their confluence, making it the true hydrological source of the Sacramento River system. Measured at the mouth, the river's natural discharge likely exceeded, a figure which includes the McCloud River and Sulanharas Creek contributing about of additional flow below the Montgomery Creek gage.
Dams
The lower course of the Pit River is one of California's most significant hydroelectric rivers, not just because of its consistent perennial flow, but because of its steep drop: in the between Fall River Mills and Shasta Lake, the Pit descends some, or a gradient of per mile, which is quite considerable for a river of its size. Because of the dependable flow, large reservoirs are not needed to regulate releases for power generation, unlike other major hydroelectric schemes in California. The combined generating capacity of powerhouses on the river and its tributaries is approximately 770 megawatts. As of 2004, the annual generation from main stem powerhouses is approximately 2.64 billion KWh. Including powerhouses on tributaries, the total rises to 3.67 billion KWh, or approximately 13 percent of California's total hydropower.The first dam on the Pit River proper is Pit 3 Dam, which forms Lake Britton near Burney about downstream from Fall River Mills. Water is diverted via a tunnel to Pit 3 Powerhouse, located on the upper end of Pit 4 Reservoir, formed by Pit 4 Dam. Pit 4 is a much smaller diversion dam, drawing water through a tunnel under Chalk Mountain to Pit 4 Powerhouse on Pit 5 Reservoir. Like Pit 4, Pit 5 is also a small diversion dam with minimal pondage. From here, the water is diverted to an offstream regulating reservoir and then through a tunnel bypassing the Pit River reach known as the "Big Bend" and the eponymous town of Big Bend, to feed Pit 5 Powerhouse. These dams and powerhouses are licensed under the Federal Energy Regulatory Commission as the "Pit 3, 4, and 5 Project", and are operated by Pacific Gas and Electric Company
Below Pit 5 Powerhouse lie two larger concrete arch-gravity dams, Pit 6 and Pit 7. These dams release water directly from the base to generate power, rather than diverting the water through long tunnels. The combined reservoirs flood almost of the Pit River. Flows for these two dams are supplemented by a diversion from the McCloud River, a tributary of the Pit River. Water is diverted from the McCloud River at Lake McCloud about south of Mount Shasta, through a tunnel to Iron Canyon Reservoir, and then through another tunnel to the James B. Black Powerhouse, which outlets into the Pit River on the upper end of Pit 6 Reservoir. These facilities are collectively known as the McCloud-Pit Hydroelectric Project and are also operated by PG&E.
The lowermost of the Pit River are flooded by Shasta Lake, which is formed by Shasta Dam on the Sacramento River about below what was formerly the confluence of the Pit and Sacramento Rivers. Completed in 1945, Shasta is a key component of the U.S. Bureau of Reclamation's Central Valley Project, a primary source of irrigation water in the Central Valley. The lake also floods parts of two Pit River tributaries, the McCloud River and Sulanharas Creek.
There are also multiple hydroelectric schemes on the Pit River's tributaries, such as the Fall River and Hat Creek. The Hat Creek Hydroelectric Project, which consists of two powerhouses on lower Hat Creek built in the early 1920s by Red River Lumber Co., is considered eligible for listing on the National Register of Historic Places. The Hat Creek facilities were purchased by PG&E in 1945.
Before environmental regulations enacted in the late 20th and early 21st century, diversions took up to 95 percent of Pit River summer flows, resulting in the dewatering of significant stretches between Fall River Mills and Big Bend. PG&E is now required to maintain base flow in the river at all times, which has led to a reduction in hydroelectric power generation but has greatly improved wildlife habitat and fishing on these sections of the Pit.