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of the Interior
The lower Colorado River extends from Lee Ferry, Arizona, the Compact Point dividing the Upper and Lower Colorado River Basins, to the Southerly International Boundary (SIB) between the United States and Mexico, a distance of about 700 river miles. The Colorado River Front Work and Levee System (CRFWLS) is a drainage and construction program to control floods, improve navigation, and regulate the flows of the lower Colorado River from Davis Dam to the SIB, a distance of about 280 river miles. Project works are located in Clark County in southern Nevada; Mohave, La Paz, and Yuma Counties in western Arizona; and Riverside, San Bernardino, and Imperian Counties in southern California.
The river in this area traverses three wildlife refuges, five Indian Reservations, and six irrigation districts. For administrative purposes, this reach of the river has been divided into 10 operational divisions. Starting at Davis Dam and proceeding in order downstream, these divisions are: Mohave Valley, Topock Gorge, Havasu, Parker, Palo Verde, Cibola, Imperial, Laguna, Yuma, and Limitrophe.
Major project facilities include the off-stream Senator Wash Dam, reservoir, and pump-generating plant; access roads, water crossing facilities, armored banklines and flood control levees. The Drop 2 Storage Reservoir project, authorized by Section 396 of Public Law 109-432, is also part of the CRFWLS.
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The CRFWLS regulates the meandering river channel in the Mohave Valley, Upper Parker, Palo Verde, Cibola, and Yuma Divisions by the use of bankline structures protected by heavy rocks (riprap) and via a riprap-protected dredge channel. Settling basins were built upstream from Topock Bridge and Laguna Dam to capture and remove some of the sediment carried by the river. Salinity control features that are part of the project include the Main Outlet Drain (MOD) and the Main Outlet Drain Extension (MODE), which convey drainage flows from the Wellton-Mohawk Main Conveyance Channel (Drain) to the Bypass Drain below Morelos Dam. The Gila River Pilot Channel was constructed to convey return flows from the irrigated lands in the Lower Gila River Valley to the Colorado River.
This project helps salvage water by controlling the size of open water areas, selective clearing of phreatophytes, drainage activities, and establishing deeper backwater areas. Major groundwater recovery programs have been undertaken by development of well fields and conveyance systems in the South Gila and Yuma Valleys, and on the Yuma Mesa.
The project has also enhanced fish and wildlife features and mitigated wildlife losses through the development of Topock Marsh, Deer Island and other backwater improvements; Cibola Lake; and Mittry Lake. Park Moabi, McIntyre Park, Walters Camp, Laguna South recreation area, and several marinas were also developed for recreation purposes.
The Mohave Valley Division extends from Davis Dam downstream to Topock, Arizona, a distance of about 43 river miles. The area through which the river flows is an alluvial valley from 2 to 5 miles wide. It traverses the Fort Mohave Indian Reservation and that portion of the Havasu National Wildlife Refuge that lies upstream from Topock. Prior to the channelization program in this Division, the river widely meandered. The deposition of sediment by the river throughout history had also caused the valley floor to aggrade (rise), so the definable channel in the lower part of the valley was almost lost as the river flowed through a series of swamps and sloughs. Stabilization was initiated in 1949 by dredging to improve a channel between Needles and Topock. This work was completed January 5, 1953, and, along with associated levee construction, minimized the immediate flooding threat to Needles, California. That same month, channel dredging, levee construction, and associated work were initiated on the reach of the river from Needles upstream to Big Bend, Arizona, about 10 miles below Davis Dam.
The average depth of the channel during dredging was about 18 feet below the water surface at a flow of 15,000 cubic feet per second (cfs). Maximum depth dredged was about 25 feet. The average design width is about 450 feet.
A total of 52,531,728 cubic yards of material was dredged in the Mohave Valley Division under this program. The total borrow for riverbanks, structures, and levees was 26,602,055 cubic yards. The design floods for levee construction in this reach of the river are: 50,000 cfs from Davis Dam to Piute Wash, and 70,000 cfs downstream of Piute Wash.
Topock Marsh is located on the Arizona side of the Colorado River midway between Davis Dam and Parker Dam. The northern portion of the marsh lies opposite Needles, California, while the southern extremity connects with the Colorado River at Topock. The marsh is almost entirely in the Havasu National Wildlife Refuge, which was established in 1941. Topock Marsh was created by backwaters resulting from the construction of Parker Dam.
Features constructed by the Bureau of Reclamation in Topock Marsh consist of inlet and outlet structures, a canal, and dikes. These structures make possible the maintenance of optimum water surface elevations in the marsh and permit diversion of water to the marsh from the Colorado River.
The Topock Marsh Dike impounds a water surface area of 4,000 acres. The materials to construct the dike were excavated by dredge from the bottom of the marsh. The highest portion of the fill rises 14 feet above the bottom of the marsh. A section of the fill northwest of the outlet structure was constructed to localize and control damage which would result from floods on the local drainage area or on the river itself.
The Topock Gorge Division starts at Topock, Arizona, and extends downstream about 12 miles to Lake Havasu. After the closure of Parker Dam in 1938, the rise in water surface elevation through this Division was accelerated and increased from 443 feet to nearly 452 feet by 1948.
The Havasu Division covers all of Lake Havasu and the river between Parker and Headgate Rock Dams, a distance of approximately 56 miles. Headgate Rock Dam was constructed by the Bureau of Reclamation for the Bureau of Indian Affairs in 1941.
Submerged trees in Lake Havasu created a navigational hazard because the reservoir area was not cleared prior to closure of Parker Dam in 1938. In 1965, removal of these tree snags, which were factors in several boating accidents on the reservoir, was begun. Three separate contracts were awarded for the underwater cutting, clearing, and disposition of the tree snags; the final contract was completed in 1971.
The design flood downstream of Parker Dam for this division is 50,000 cubic feet per second.
The Parker Division begins at Headgate Rock Dam and extends downriver about 33 miles to Palo Verde Diversion Dam. The channel throughout this reach has been subjected to scouring action by clear water releases from Parker Dam; after it was constructed, Headgate Rock Dam stabilized the channel below Parker Dam. The area below Headgate Rock Dam is protected from floods by the levee system built in conjunction with the construction of Palo Verde Diversion Dam.
Parker Division is divided into two sections. Section I lies within the Colorado River Indian Reservation and extends about 16 miles downstream from Headgate Rock Dam to Alligator Bend. Section II embraces the river from Alligator Bend to Palo Verde Diversion Dam, a distance of about 28 miles. The Arizona side and the northern part of this section that is in California are within the Colorado River Indian Tribes' (CRIT) Reservation.
Stabilization of the river in section I was accomplished by confining portions of it between training structures (structures that guide or control the flow of water) or stabilized bank lines. The basic channel improvement work was completed in 1967.
In 1969, a comprehensive plan for channel stabilization in section II was approved by the Department of the Interior. However, the work was deferred pending the location of the western boundary of the CRIT Reservation. In 1971, a task force appointed to review the River Management Program recommended that additional plans for the Parker Division below Alligator Bend be considered to reduce the environmental impact of the work. Several alternative plans involving a reduced program were evaluated but none were adopted. In the early 1990s a new plan was developed and implemented. It included armoring banklines with riprap, as well as the placement of training structures and jetties. In addition, a backwater was created at Aha Quinn on the CRIT Reservation, with two new channels created by dredging, and a third channel, in an existing drain, cleaned and restored. The completion of this work contributed significantly to the reduction of sediment originating from the Parker II Division.
The design flood for this area is 50,000 cubic feet per second .
The Palo Verde Division extends about 28 miles from Palo Verde Diversion Dam to Taylor`s Ferry. Channelization of the river in this Division began in May 1962 and was completed in September 1968. The work consisted primarily of constructing earthfill training structures and protecting riverbanks with riprap to prevent future meandering of the river. Many of the backwater areas created by the training structures were improved to benefit fish and wildlife.
The Bureau of Reclamation also participated in the development of Blythe Marina and McIntyre Park, which are presently administered by Riverside County, California. Dredging of the Blythe Marina began in June 1966 and was completed in February 1967. Dredging of McIntyre Park to deepen the backwater for recreation purposes was begun in July 1972 and completed in December 1972.
In addition to providing channel stability and 10,000 acre-feet of annual water salvage, the completed river stabilization work reduced the sediment load originating in the Palo Verde Division, thereby reducing the amount of material carried downstream.
The design flood for this section of the river is 75,000 cubic feet per second.
The Cibola Division extends about 24 miles downstream from Taylor`s Ferry to the Cibola gage at the lower end of Cibola Valley.
Prior to any Reclamation activities in the area, the channel through this division was characterized by a transition from degradation at the upper end to aggradation at the lower end, resulting from the adjustments that had taken place since construction of the storage dams upstream. The river had acquired a large sediment load in passing through the Parker and Palo Verde Divisions and the erosive force of the flow was reduced greatly by the time it arrived at the upstream end of the Cibola Division, causing much of the sediment to settle in the river channel. Immediately following the closure of Parker Dam, a balance point formed near the mouth of the Palo Verde Drain, with degradation above and aggradation below. The aggradation caused the water surface in the Palo Verde Drain to rise, which also raised the groundwater table through the lower third of the Palo Verde Valley.
The CRFWLS provided some relief to this situation in 1947 by moving the confluence of the river and the drain downstream about 2 miles. This was accomplished by constructing a pilot cut across a bend in the river and letting the drain use the old channel down to the new channel. This cutoff was successful in dropping the water surface at the drain gage by about 1.5 feet, but it did not lower the water surface elevations in the drain enough to completely solve the problem.
Through much of the Cibola Division, the natural channel was shallow due to sediment deposition. A program to dredge the channel and construct levees was initiated in 1964 and completed in 1970. The dredged channel begins 2.2 miles downstream from Taylor`s Ferry and ends at the lower end of Cibola Lake near Adobe Ruins. Major features constructed to preserve fish and wildlife in the area include the backwater improvement of the Palo Verde Oxbow Lake south of Palo Verde. Another area improved for fish and wildlife is Cibola Lake, in the Cibola National Wildlife Refuge that was established in August 1964.
The work in the Cibola Division provides an estimated 36,000 acre-feet of water salvage yearly, and has substantially reduced the sediment passing into the Imperial Division.
The design flood for this division is 80,000 cubic feet per second.
The Imperial Division extends from the Cibola gaging station to Imperial Dam, a distance of about 36 river miles.
This division consists of the diversion pool and associated backwater areas above Imperial Dam. It is the recipient of the sediment generated in the Parker, Palo Verde, and Cibola Divisions.
Sediment carried downriver from Parker Dam is deposited in the river and associated backwater areas above Imperial Dam; about 50 percent is deposited on sandbars in the channel or in backwater lakes; the remainder is diverted at Imperial Dam. Most of the diverted sediment is removed from the water by the All-American Canal Desilting Works. The sediment removed from the water by these works is then sluiced to the Laguna Settling Basin below Imperial Dam and just above Laguna Dam. It is removed from this area to dry land storage.
Sediment filled a number of backwater areas above Imperial Dam after it was constructed, particularly in the upper end of the division. Others backwater areas were isolated from the river by natural, river-formed dikes. This condition led to deterioration of the water quality and fish and wildlife values in these isolated backwater areas. Maintenance activities have been conducted over the years to clean these areas out and restore their environmental qualities, and to maintain water diversions from Imperial Dam into the headworks of the Gila Gravity Main Canal.
The design flood for this reach of the river is 80,000 cubic feet per second.
Senator Wash Dam, Reservoir, and Pumping Plant -- Imperial Division
Senator Wash Dam and Reservoir, an offstream pumping facility, is located about 18 miles northeast of Yuma, Arizona, on the California side of the Colorado River 2 miles upstream from Imperial Dam and at the river-end of Senator Wash. The dam is at the mouth of Senator Wash, which flows from California into the river. It was constructed to improve the management of Colorado River water deliveries.
Three days are required for water released at Parker Dam to reach Imperial Dam, so changing conditions like rainy weather or unexpected maintenance work on water delivery systems, can require water requests to be cancelled. Senator Wash enables some of these flows to be diverted and later released back into the river when they are needed. This is accomplished by pumping into Senator Wash Reservoir some of the scheduled water deliveries that are not needed when they arrive at Imperial Dam, then later releasing the water back into the river for downstream use.
The principal features are an earth dam, three dikes, a spillway, an outlet works, a pumping plant, a switchyard, and access and service roads. A 69-kilovolt transmission line, about 18 miles long, constructed separately by the Parker-Davis Project, is now operated and maintained by the Western Area Power Administration of the Department of Energy.
Senator Wash Dam is a three-zone rolled earth embankment structure 2,342 feet long, with a maximum structural height of 93.6 feet. Squaw Lake Dike is a three-zone rolled earth embankment structure 3,795 feet long, with a maximum structural height of 95.3 feet. North Dike is a two-zone rolled earth embankment structure 613 feet long, with a maximum structural height of 67.2 feet. A small single-zone rolled earth embankment structure was constructed in a small saddle on the right abutment of Senator Wash Dam and is included in the dimensions for the dam. A 3-foot layer of riprap was placed on the upstream slope of all the earth embankments. A 24-inch-thick impervious blanket, extending from the upstream toe of the dam, was constructed on the floor and slopes of the reservoir to elevation 210, the top of inactive storage.
An equalization channel uses the storage capacity of a small isolated basin behind North Dike.
The outlet works consist of an intake structure, a 10-foot-inside-diameter concrete conduit, a 6.5- by 10-foot-high pressure gate in a gate chamber, a 10-foot-inside-diameter steel pipe installed inside a 15-foot-inside-diameter concrete conduit, an access house, a concrete-encased steel manifold, and six 54-inch steel branchlines leading to the pump turbines.
The Senator Wash Pumping Plant is of the indoor type with a reinforced concrete substructure and steel framed superstructure. Six (including one spare) vertical-shaft, single-suction, centrifugal, Francis-type pump-turbines with fixed-vane diffuser-type casings are installed in the plant. Each pump-turbine is directly connected to a vertical shaft, 360-revolution-per-minute, synchronous motor-generator designed to operate either as a motor or as a generator. A 20-ton, fiber-operated overhead traveling crane is provided for installing and maintaining the unit. Although originally conceived as a pumping-generating plant, it was designated as a pumping plant in 1977.
When operating as a pumping plant, each 1,750-horsepower pump is designed to operate from 31 feet of head to shut-off head and will deliver not less than 100 cubic feet per second at a total head of 74 feet while operating at 360 revolutions per minute. Under normal operations, each unit pumps about 200 cubic feet per second. Normal starting and stopping of the unit is controlled from the remote control panel at Imperial Dam, which includes all the electrical control equipment (switching, alarm, and indicating) required for remote operation of the pumping plant.
A 17.7-mile, 69-kV transmission line between Gila Substation and Senator Wash Substation brings power for pumping to Senator Wash, about 10,000 kVA when all six pumps and all station loads are in operation.
Senator Wash Dam has experienced structural problems that have limited the storage space that can be used to temporarily store water. It is now operated with a storage capacity of about 11,000 acre-feet, or about half its designed capacity.
The Laguna Division was designated to facilitate the construction and operation of the Laguna Settling Basin and the appurtenant channels leading to and from the basin. It includes the 4.7-mile reach of river between Imperial and Laguna Dams.
The settling basin operation in the Laguna Division was originally adopted as a result of a general complaint lodged by Mexico that the United States was reintroducing sediment into the river in amounts that represented higher concentrations than were present in the river when it reached Imperial Dam. Removal of the sediment by dredging rectified the situation. Dredging of Laguna Settling Basin began in 1963 and was completed in 1965. About 1.2 million cubic yards of material were excavated.
The settling basin operation fulfills two primary objectives: removing the additional sediment that was being carried to Mexico, and reducing the amount of water that was being used for sluicing.
Mittry Lake was also developed as a fish and wildlife management area by using heavy equipment to remove the extremely heavy tule (bulrush) growth and accumulation of extensive floating mats of vegetation in the area.
Dredging of the Gila Sluiceway began in 1970 and was completed in 1973. This sluiceway carries sediment flushed from the Gila Main Canal Desilting Basin to the Laguna Settling Basin.
The Yuma Division of the CRFWLS includes 21 miles of river channel between Laguna and Morelos Darns. The City of Yuma is on the south bank of the river, approximately in the center of the division. The channel in this division reflects changes resulting from construction of storage dams and diversion of water for irrigation purposes upstream. It consists of a small active channel situated within a larger, older riverbed which is entrenched below the historic level of the unregulated river.
The flow into the upper end of the Yuma Division is regulated primarily by Laguna Dam. It normally consists of water used to flush sediment from the All-American Canal Desilting Works into the Laguna Settling Basin, and from sluice-gate leakage and intermittent sluicing flows below Imperial Dam. Laguna Dam is used to re-regulate the flows originating at Imperial Dam.
About 9 miles downstream from Laguna Dam, the Gila River enters the Colorado River from the east. The flow from the Gila River is the result of returns from canal wasteways, drainage from irrigation areas, and occasional floodflows. Since 1977, flows from the Wellton-Mohawk Irrigation and Drainage District drainage wells, which were frequently discharged into the Colorado River downstream of Morelos Dam, have been carried to the Santa Clara Slough in Mexico in a concrete-lined canal (bypass drain).
The California Wasteway of the Yuma Main Canal is about 4 miles downstream from the mouth of the Gila River, across the river from Yuma. This wasteway returns water to the Colorado River to help fulfill the United States' Treaty obligation to deliver to Mexico 1.5 million acre-feet of Colorado River water annually.
Rockwood Heading, a historic intake structure on the Alamo Canal, is about 2 miles upstream of Mexico's Morelos Dam. It is no longer used as an intake structure, but now functions as a point of return for the Pilot Knob Powerplant and Wasteway from the All-American Canal.
Before the Laguna Settling Basin was completed in 1965, the Colorado River carried a comparatively heavy load of sediment into the upper end of the Yuma Division as a result of the All-American Canal Desilting Works and periodic sluicing of Imperial Reservoir. The Laguna Settling Basin now intercepts the sediment below Imperial Dam and the trapped sediment is dredged out of the basin and pumped onto adjacent land. As a result, the water entering the Yuma Division is relatively sediment-free,
The early history of the Yuma Division shows that lateral movement of the river occurred infrequently. A major channel change occurred in 1920 and created what is commonly known as Yuma Island. Located about 3 miles northeast of Yuma, the island is a floodplain partially encircled by the pre-1920 river channel. This channel is filled with sediment except for the two small depressions which constitute Haughtelin and Bard Lakes.
Protection from flooding in the low-lying valley lands was provided throughout most of this division by an arrangement of levees constructed during the early activities of the CRFWLS; most of these levees were rehabilitated in 1951 and 1952.
During the rehabilitation of the Yuma levee system, the Upper Reservation Levee was relocated parallel to the existing river channel. This change re-established the levee closer to the active channel of the river and left a fairly large area of land between the 1905 alignment of the levee and the relocated levee.
Studies conducted in 1948 by the International Boundary and Water Commission, the U.S. Army Corps of Engineers, and the Bureau of Reclamation established a design flood for use in designing the heights of the lower river levees. The flows accepted were 103,500 cfs from Imperial Dam to the mouth of the Gila River and 140,000 cfs below the mouth of the Gila River. Additional studies were made by the International Boundary and Water Commission concerning the effect of Morelos Dam on upstream water stages as related to levee design in the Yuma Division. The existing levee system in the Yuma Division was designed using the data from those studies.
The division is protected from floods by the Reservation and Yuma Valley Levees. The Reservation Levee protects the lands to the west of the river from Laguna Dam to the high lands below Yuma. The Yuma Valley south of Yuma is protected by a levee on the south and east side of the river from Prison Hill to the Southerly International Boundary.
The South Gila Levee protects the lands to the south of the river from the mouth of the Gila River to Prison Hill, and an extension east along the south side of the Gila River to the siphon of the Gila Gravity Main Canal, where it joins the Corps of Engineers' Gila Levee System, giving full flood protection to lands in the South Gila Valley.
In 1962, Congress appropriated funds for initial investigation of a plan for groundwater recovery and drainage relief in the Yuma Valley that would also help regulate flows in the Colorado River.
The groundwater recovery plan was enlarged in scope to include the entire Yuma area groundwater basin and to increase the river regulation aspects. A study was completed and a plan developed in July 1964. Construction of the first phase, Valley Division, Conduit No. 1, was initiated in 1965. Mexico objected to the groundwater program in Yuma Valley, stating that it would increase the salinity of waters delivered to Mexico and replace Colorado River water entitlement to Mexico with pumped groundwater.
As a result of a conference with Mexico on October 12, 1965, the Bureau of Reclamation revised its groundwater recovery plan in Yuma Valley. The wells were relocated along the east side of the valley near the toe of the Yuma Mesa, thereby minimizing interference by groundwater pumping with the underflow to Mexico. The revised plan provided for the conveyance of part of the water north to the Colorado River, and the remainder by Yuma Valley drains to Mexico at the Southerly International Boundary. Under all conditions, the plan provided for drainage improvement and substantial groundwater recovery and river regulation benefits.
To conduct the recovery program with minimum impact upon Mexico, alternative well locations were studied to determine the feasibility of relocating the well field on the Yuma Mesa near its western edge. Because additional drainage in Yuma Valley was badly needed, six drainage wells were constructed by the Bureau of Reclamation in addition to the seven wells developed by the Yuma County Water Users' Association along the eastern toe of the Mesa. The discharge from these wells is conveyed through a conduit system to the Yuma Valley Division of the Yuma Project drainage system at the Southerly International Boundary as part of Mexico's entitlement to Colorado River water.
Another segment of the Yuma area groundwater and river regulating program is the Drain Pump Outlet Channel (DPOC) drainage system in the South Gila Valley. It consists of 24 drainage wells. Three of the conveyance conduits of this drainage systems discharge into the Gila River Pilot Channel, constructed as part of the CRFWLS in 1961. The fourth conduit discharges the pumped drainage water into the Colorado River.
The DPOC drainage well field provides drainage for the agricultural lands of the South Gila Valley and returns this water to the Colorado River to become a part of Treaty water delivered to Mexico above Morelos Dam.
The Yuma Mesa Well Field, a segment of the overall groundwater and recovery and river regulation program for the Yuma area, is located along the western edge of Yuma Mesa. The groundwater recovered by this well field is collected in a conduit system and conveyed to the Colorado River near Yuma.
Integrated into the Yuma Mesa Well Field system are six wells which were installed in Yuma Valley in 1965. Currently there a total of seven wells with the last one being installed in 1997. These wells are located along the western toe of Yuma Mesa and their discharge is conveyed through concrete pressure pipelines to the Valley Division drainage system.
The principal functions of the groundwater recovery program are to recover from the groundwater basin return flows from irrigation developments in the United States to assist in meeting requirements for delivery of water to Mexico, to provide some drainage relief for the Valley Division of the Yuma Project, and to assist in Colorado River operations by reducing over-deliveries to Mexico.
The Yuma Mesa Well Field consists of 12 wells, spaced about 0.5 to 1 mile apart. It is operated by remote control from Imperial Dam by the use of radio signals to actuate the individual pumping units and monitor the operation through electronic interrogation. The well field, operated on a 24-hour basis throughout the year, is capable of pumping about 40,000 acre-feet of groundwater annually. In addition, about 9,000 acre-feet of water are pumped annually from six Bureau of Reclamation drainage wells developed in Yuma Valley.
The Colorado River at and downstream of Morelos Dam forms the boundary between the United States and Mexico. Proceeding downstream for a distance of 20 miles, the left (east) bank of the river is in the United States and the right (west) bank is in Mexico. The river has levees on both sides of the river; the levee on the Mexican side is about 4 feet higher than the levee on the United States side.
The conditions between Morelos Dam to the Southerly International Boundary were not typical of ordinary river conditions, in that no degradation existed downstream of the dam. In fact, the gated portion of the structure did not always form the water surface control that would normally be the case. A downstream plug of sediment introduced in the channel below Morelos sometimes controlled the water surface elevation through the gated structure.
This sediment plug was unintentionally created by the operation of a Mexican dredge in the settlement basin at the head of the Alamo Canal, and the method of disposal of sediment employed by Mexico at Morelos Dam. The Alamo Canal desilting basin is an over-width and over-depth section of the canal that runs generally parallel to the river. For several years following the completion of Morelos Dam, sediment was pumped out of the desilting basin onto the ground between the basin and the river. Over a period of years, the disposal area was built up by the deposition of dredge spoil until the sediment could not be pumped any higher.
The sediment was then pumped into the river and along the bank between the Mexican levee and the river. On occasion, the sediment deposit has deflected the current of the river against the bank in the United States side of the river, causing erosion. When this occurred, Mexico deposited some of the sediment spoil on the United States side to repair the erosion and return the river to the center of the channel. This type of operation has kept the river away from the United States levee, but has built up the bed of the river with a sediment plug consisting of several million cubic yards of material.
The remainder of the river channel from Morelos Dam to the Southerly International Boundary has historically been choked by sediment carried downstream from the sediment plug. Also, because Mexico customarily diverts most of its Colorado River water supply into the Alamo Canal above Morelos Dam, the flow below Morelos Dam is generally minimal, and the channel is overgrown with vegetation, seriously reducing the channel's flood-carrying capacity. Work has been conducted in the Limitrophe Division periodically to address this situation. Because this division of the river is an International Boundary, all work activity, planning, or construction is coordinated with the International Boundary and Water Commission.
The Colorado River Front Work and Levee System is maintained and operated by the Bureau of Reclamation.
In its natural state, the Colorado River experienced seasonal floods during part of the year and a shortage of water the remainder of the year. It also carried a heavy silt load, and the flow was too erratic to support year-round navigation or use. Regulation of the river was accomplished by constructing dams to store some of the annual flow, plus supplemental downstream works at critical locations to solve localized problems.
Subsequent to the construction of the various dams on the river, the river channel was subjected to severe degradation (channel lowering) downstream and aggradation (channel raising) upstream from a dam. In the wide river bottoms of Mohave and Cibola Valleys, the river surface was raised by continued aggradation until the banks were overtopped and swamps of considerable magnitude were created.
Because of the immediate hazard to the city of Needles, emergency work was undertaken in 1944 to enlarge the existing but inadequate levees along the Colorado River. The initial channelization work, Needles to Topock, was aimed at alleviating the flood and high-water hazard to the city of Needles and the facilities of the Atchison, Topeka, and Santa Fe Railway Company in Mohave Valley .
At Palo Verde Irrigation District's intake, 65 miles downstream from Parker Dam, degradation had lowered the riverbed to the point that diversions could not be made satisfactorily. Rock placement for a temporary weir designed to raise the river level high enough for diversion began on January 12, 1945. On June 24, 1945, the first water was delivered through the district's new headworks upstream from the weir. Completion of the weir permitted full gravity diversion to be resumed through the canal system, but continuing difficulty made construction of a new diversion facility necessary.
Investigations by the Bureau of Reclamation revealed the need for a concerted, continuing project for an indefinite period to control the operation of the river efficiently.
The Colorado River Front Work and Levee System was authorized by the Act of March 3, 1925 (P.L 585), which was subsequently amended by the Acts of January 21, 1927 (P.L. 560), July 1, 1940 (P.L. 697), June 28, 1946 (P.L. 79-469), and May 1, 1958 (P.L. 85-389). The Colorado River Floodway Protection Act (P.L. 99-450) and Section 396 of the Tax Relief and Health Care Act of 2006 (P.L. 109-432) also provide authorization for project activities.
Mohave Division - Enlarging the existing levees along the Colorado River began in 1944. The initial channel stabilization, levee construction, and associated work, Needles to Topock, commenced in 1949 and was completed in 1953. Channelization and levee construction by dredging, Needles to Topock, started in 1953 and was completed in 1960. The Topock Settling Basin was constructed by dredging between December 1955 and November 1956. Dredging of Park Moabi started in 1964 and was competed in 1965. Work on the main dike of Topock Marsh was initiated in 1965 and completed in 1966 with the installation of the marsh`s inlet and outlet facilities. Improvement of the Needles Marina was started in 1967 and completed in 1968. The Big Bend training structure was constructed between January and June 1969. Improvement of Park Moabi by dredging was accomplished during December 1971 and January 1972. Fish and wildlife habitat improvement of Topock Marsh started in January 1974 and was completed in 1980.
Topock Gorge Division - Dredging of the Upper Topock Gorge began in 1967. However, the dredging was suspended in 1968 following objections by the U.S. Fish and Wildlife Service.
Havasu Division - Snag removal in Lake Havasu was accomplished intermittently between December 1965 and June 1971.
Parker Division - Construction of bankline structures for the Parker Division, Section I, with land-based equipment, began in January 1966 and was completed in June 1968. Improvement of Deer Island by dredging began November 1968 and was completed in May 1969. In the early 1990s several training structures were completed and eroding banklines were armored with riprap.
Cibola Division - Channel dredging and levee construction between Taylor Ferry and Adobe Ruin started in June 1964 and was completed in December 1969. Construction of the lower Cibola Bridge was initiated in June 1969 and was completed February 1970. The Cibola dry cut was opened March 10, 1970. The Palo Verde Oxbow was dredged in 1970 and supplemental bankline work was completed by contract from May 20 to November 17, 1971. In 1974, the mouth of the old river channel near Walter`s Camp in the lower Cibola Valley was dredged and the river bankline structure was extended to narrow the old river channel and provide boating access to the improved Walter`s Camp recreation area. The Cibola Lake inlet and outlet structures were built in 1974.
Imperial Division - Silt removal activities have been carried on intermittently above Imperial Dam since 1969 to relieve the flow into the Gila Canal. Construction of Senator Wash Dam, Reservoir, and Pumping Plant was accomplished from 1964-1966.
Laguna Division - Construction of the Laguna Settling Basin by dredging began in July 1963, and was completed in April 1965. Construction of a freshwater inlet channel to Mittry Lake, and the dredging of Mittry Lake and the Gila Sluiceway started in 1970 and was completed in 1973.
Yuma Division - Raising of Yuma Levees and construction of the Reservation Levee began in May 1951 and were completed in September 1952; dredging to relocate the channel was completed in 1954. Construction was started on the Main Outlet Drain and the Gila and South Gila Levees in 1960 and completed in 1962. Construction of the Valley Division Conduit No. 1 and drainage well field was started in 1965 and completed that year. The Yuma Mesa Well Field and conduit were constructed during 1968-1971, and the South Gila Valley drainage wells and drainage pump outlet channels were constructed in 1964. The Main Outlet Drain Extension was constructed in 1965.
The project has increased water supplies by reducing water loss from evaporation and by improving the flow of the water in the river channel. It has also enhanced the fish, wildlife and recreation values of the lower river area; improved navigation; improved diversion management; reduced the river's silt load; assisted in the control of floods and salinity; and provided needed technical information for future efficient river operation.
The CRFWLS has enabled several areas along the river to be developed for recreation; click on the links below to learn more:
Topock Gorge and MarshCibola Lake Mittry Lake and Wildlife AreaPark MoabiBetty's Kitchen National Recreation TrailSenator Wash Boat Ramp and Day Use AreaSquaw Lake Campground