Grand Prairie project demands years of engineering work.
But the water management project that covers parts of four counties is not designed for navigation; it's a conservation project designed to slow the depletion of the alluvial and Sparta aquifers by taking water from the White River for the irrigation of crops and leaving the pure water of the aquifers for the area's towns.
And although it has been the object of much controversy and failed litigation by various environmental groups, the Memphis District of the Army Corps of Engineers, which oversees the project, claims it will "provide critical benefits for the millions of waterfowl, which annually migrate through the region."
Garver Engineers of Little Rock, the state's largest engineering firm, has the lead role in designing the intricate system of canals and gates, pipelines and a big pumping station at DeValls Bluff. It's a project Garver started working on in June 1998 and continues to this day.
Located between the White and Arkansas rivers, the Grand Prairie region is one the state's most productive agriculture regions, but the lay of the land also makes for a complicated solution to ease the looming water crisis.
The project covers some 362,000 acres, said Paul Hamm, project manager for the Army Engineers. Of that, 254,000 acres are cropland, and, of that, 247,000 are irrigated.
Farmers in the region have been tapping the aquifer groundwater since rice became the dominant crop. While Arkansas produces just under one-half of all the rice grown in the U.S., those who grow it are taking water out of the ground faster than it can be recharged from rivers, streams, bayous, rainfall and percolation of water downward through soil.
That means the water table continues to decline. If nothing is done, Army Engineers studies predict the alluvial aquifer will be commercially useless by 2015.
The problem of water for the region's crops has been around for close to a century, since water-loving rice began to be the prime crop. Ideas for some system to divert surface water have been tossed about for the past 50 years, said Tom Fortner, deputy director of the White River Irrigation District, the local nonprofit entity that will operate and maintain the project.
But nothing much was done until the mid-1980s when a study by the Arkansas Soil & Water Conservation Commission (now the Arkansas Natural Resources Commission), began recording just how fast the region's groundwater resources was shrinking. From that and other studies, Congress in 1991 authorized the Army Engineers to develop the Grand Prairie Area Demonstration Project in partnership with ANRC, the U.S. Agriculture Department's Natural Resource Conservation Service and the WRID to find and implement a solution to groundwater depletion problem.
Regardless of how one feels about the potential merits and possible drawbacks to the project, it is a huge and complex project that calls into use multiple engineering disciplines--structural, civil, mechanical, electrical, surveying and geo-technical.
Essentially, "it's like creating a river in reverse," said Brode Morgan, vice president of system engineering at Garver. Some 20 engineers at the company have been involved at one time or another in designing parts of the project.
Some of it remains to be designed. The pumping station alone, on which work began last spring, took two years to design. The pumping station, the first phase of the project, is expected to be completed in July 2007, Former said. It is being built by Granite Construction Co. of Watsonville, Calif.
The three-level, $35 million pumping station will be capable of delivering 1,640 cubic feet of water per second during specific times of the year, which translates to 736,000 gallons per minute.
The pumping station includes six pumps. Four are 84-inch pumps powered by 6,000-horsepower motors capable of pumping 360 cfs each. The other two are smaller 42-inch pumps powered by 1,500-horsepower motors that can pump 100 cfs each.
The pump discharges move through two 10-foot-diameter pipes that send the water out to a 50-foot-wide, flat-bottomed canal that has approximately 350 feet of right of way; the canal and levee system will eventually bring the water to some 900 farms in the region.
The Army Engineers maintains that the impact of the pumping station would be minimal--that the total flow of the river being diverted is only 1.5 percent in an average flow and less than one-half of I percent during duck season.
The pumping station, however, is but one of 15 items on which Garver and its partner in the massive project, Neel-Schaffer Inc. of Jackson, Miss., are working. Morgan said the company is now up to item 10.
Morgan said the Army Engineers felt the project was too big for one firm to handle. Garver and Neel-Schaffer have divided the 15 items making up the project, but Garver has the management role.
Garver also brought in FTN Associates Ltd. of Little Rock, an engineering firm that specializes in water resources and floodplain management, to assist in the design:
Laying out the canals, which could total some 102 miles, and the 290 miles of underground pipe to water the farms may be the major part of the project, but just as important is the network of on-farm reservoirs that will be built to hold the stored water.
The beauty of the project, said Hamm, is that it's not solely taking water from the White River, but it's a "combination that takes advantage of what nature provides and simply supplements it with water from the White River."
New reservoirs will be built on approximately 8,800 acres. On an as-needed basis, farmers will use the stored water to irrigate their crops or flood their rice fields. Water that doesn't sink into the ground for use by the plants or evaporate will be recovered by a ditch and pipeline system and pumped back to the reservoir--called a tailwater system.
The reason for the on-farm reservoirs is that withdrawals from the river will be limited at certain levels and at certain times of the year, such as when fish are spawning.
Between 85 and 90 percent of water used for irrigation now comes from the alluvial aquifer. Once the project is completed, it is expected that 51 percent will come from the White River, 42 percent will be supplied by the on-farm reservoirs and 7 percent will come from wells, which should allow the aquifer to recharge, WRID's Fortner said.
These on-farm conservation features will cost about $80 million, with the federal government picking up 65 percent of the tab. Work has been under way for a couple of years on the reservoirs, but it could take another six or seven years to complete all the pieces of the projects, depending on congressional approval of funding.
The Army Engineers must seek funding from Congress each year, Hamm said. Only about a third of the cost of the pumping station has been funded, he estimated, but he expects that part of the project to be completed on time.
The remaining 35 percent of the cost of the project--the nonfederal share --will come from the Arkansas Natural Resources Commission and the White River Irrigation District.
Farmers or landowners have anted up about $14 million so far for the on-farm reservoirs; the state, about $18 million. The plan is for the state to offer deferred loans to the White River Irrigation District that will be repaid with revenue generated through the sale of water. Farmers or landowners in the WRID also will have an annual assessment of $1 to $3 per irrigated acre.
Morgan said the volumes of data created by staff engineers since Garver was given the job have resulted in numerous design changes based on computer simulation models.
For instance, he said, the canal will have check structures, which were originally supposed to incorporate vertical slide gates to control the flow. But that was changed to radial gates, which can more precisely control the flow of water.
The canal design, Morgan said, has had to contend with crossing roads, which calls for bridges; with natural streams, which will be siphoned underneath the canal; and, with utilities such as power lines and utility lines, which will have to be routed underneath or over the canal.
The canal will run along roads for the most part, following property lines and county roads and cutting as little as possible across any farmer's land. The initial route of the canal was planned by the Natural Resources Conservation Service and finalized by the Army Engineers and WRID based on engineering, environmental and economic factors.
One obstacle Garver encountered was the Hazen airport, which it went around, Morgan said, And there's one railroad that crosses the region, he said, and railroads always take priority, so the canal will have to be routed underneath it.
The final design of the main canal under the railroad is not complete, but the design concept is based on a combination check structure with multiple conduits to convey the canal under the railroad, Morgan said.
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|Title Annotation:||by Granite Construction Inc.|
|Comment:||Grand Prairie project demands years of engineering work.(by Granite Construction Inc.)|
|Date:||Mar 20, 2006|
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