The Colorado River system is facing the worst drought on record. Lake Mead's water level has dropped >150' THE PROBLEM:
During the 20th century, floods were the number-one natural disaster in the United States in terms of the number of lives lost and property damage.Droughts have caused farmlands to dry up putting tens of thousands of workers out of work. INTEGRATED SOLUTIONS:
Water can be captured during a flood along a river levee wall by using a patent-pending modified levee that has an approximately 1000 ft long continuous 2-ft wide slotted steel drain into a pipe-arch shape corrugated structural plate steel pipe (concrete lined) buried along the levee wall. The opening of the slotted drain should have strong grating covered by a 1/4 inch mesh screen to prevent most debris and living animals from entering the capture pipe. The capture pipe could use a pipe-arch design with a span of 16.5 ft and a rise of 11 ft or more. The elevation of the slotted drain should be at the Action Stage elevation for the primary capture pipe. A secondary or tertiary capture pipe could run parallel to the primary capture pipe with a slotted drain entrance at the Flood Stage elevation to capture more water during the flood event. The primary drain at Action Stage and secondary drain at Flood Stage and tertiary drain at Moderate Flood Stage provide a set of steps integrated into the river levee wall parallel with the river. The use of corrugated steel pipe (CSP) buried in the river bank contour allows the water to flow downstream in the modified levee capture pipe to a designated location where the captured water could be collected into retention ponds located adjacent to the river bank. A pipe arch design has hydraulic advantages at low flow and should accommodate this application. The river surface elevation over Action Stage or Flood Stage or Moderate Flood should provide ample head to move the water from the river to the retention ponds. The use of concrete lined CSP should be considered for its strength and low hydraulic resistance, especially between the river bank capture pipes and the retention ponds. The Manning formula, used to calculate the flow from the river withdraw point to the retention ponds, is a semi-empirical equation for simulating water flows in the capture pipe where the water is open to the atmosphere, i.e. not flowing under pressure. This equation is valid during Action Stage where part of the slotted grate is not yet inundated. However, once the river water reaches flood stage or completely covers the slotted opening, then the capture pipe or withdraw pipe will become pressurized and the resulting flow will increase exponentially. Q = VA V = (1.486/n) R2/3 S1/2
where, Q is discharge flow rate (ft3/s or cfs)
V is velocity (ft/s)
A is Area (ft2), (an arch pipe with span of 16.5 ft and rise of 11 ft has an area of 142 ft2)
n is coefficient of roughness (steel is rougher than concrete: use concrete where possible)
R is hydraulic radius (ft) also expressed as A/P
S is hydraulic gradient (ft head loss/ft length) (use a slope of 10’/100’ to a retention pond)
P is wetted perimeter
The size of the retention ponds (that feeds the primary pumps and pipelines) could be large enough to hold significant flood water for uniform continuous pump operation. A parametric study could determine the optimum size at a given capture location considering the various input and output rates to/from the retention ponds. A suggested size for initial consideration would be 50 to 100 million gallon capacity. It should be located below the arch-pipe elevation to enable gravity feed from the capture pipes into the retention ponds. The retention ponds will be connected to pumps that are in turn connected to the pipelines/aqueducts. The size of the retention ponds (that feeds the primary pumps and pipelines) could be large enough to hold significant flood water for uniform continuous pump operation. Large pumps capable of moving 1200 cfs or more (powered by ~ 80,000 hp motors) are expected to drain the interim retention ponds and feed the pipelines. The pumps should auto-actuate above a specified water level in the retention ponds. The pump motors could use natural gas as a fuel in internal combustion reciprocating engines or be powered by three-phase electricity. Pumps of this size could be made by American manufacturers such as ITT Flygt, who recommended use of a fabricated dry pit spilt case pump. The flow of 1200 cfs is large, but attainable in a single pump. A single pump could produce 1200 cfs flow with approximately 500 ft Total Developed Head (TDH) and would require an approximately 80,000 hp motor. Pumps of this size have been developed since the 1950s and can still be built today. A lift of 5000 vertical feet would require 10 pumps spaced at about 500 ft of vertical elevation. The pumps actually produce about 560 ft TDH, but the pipe has inherent friction or hydraulic drag, so spacing retention ponds and pumping stations at 500 ft seems reasonable for a preliminary conceptual design. A parametric study considering volume, displacement, suction head or lift to next pump or storage location, efficiency, and energy use will determine the optimum size(s) and type. The number of pipes from the interim retention ponds to destination will vary depending of the volume and rate of water captured and moved. The data in the Appendix 1 spreadsheet gives the Action Stage elevation (ft amsl) for each river gage location and could be used to provide an approximate elevation of the first retention ponds and pumps. Valves should be appropriated located having remote control connected to water level in the collection ponds and destination data. Captured fresh water has to be transported several hundred miles to the existing water agencies. Where the distance is very large, transportation of the water can no longer be accomplished by one pumping station alone, since the frictional losses are too big. The pipelines would have to be designed to operate at higher pressures, and the pipeline wall thickness would have to be increased. Costs of the pipelines would rise with the increase in wall thickness. The extra costs for additional pumps and motors are, however, hardly significant compared with the potentially higher pipeline costs (Bolliger, 2004). Hence, the required total delivery head is distributed over several pumping stations (analogous to the Alaska Pipeline). Distribution is arranged to match the topographical conditions of the terrain. Suggested pump material to be employed is cast steel (with surface protection), with the impeller usually made from chromium steel. When designing water transport pumps, particular attention has to be paid to achieving low operating costs, as the operating costs predominate over the purchase price. When calculating the economic performance, it is necessary to take the efficiency of the pumps into account. The efficiency rises with increasing impeller size. This is brought about by the fact that greater pumping capacity is achieved by increased impeller diameter, which in turn requires a greater flow cross section and reduces the effect of the boundary layer. The drivers for large water transport pumps are usually three-phase electric motors. However, natural gas powered motors could provide a very significant energy cost savings over electric motors and investigation into this technology is warranted. If each pipeline were to have one pump per 500 ft elevation than as many as 144 pumps could be required for the 3,200 miles involving pipelines P1 thorough P4. has an abundant natural gas supply throughout the same area as the pipelines and it is expected to remain abundant over the projected 100 plus year facility life. Using natural gas as fuel for the large motors would not cause any stress on the national electric grid and the cost per Mw of energy is lower comparing natural gas with electricity. Use of hybrid natural gas/electric motors should be evaluated to consider use of natural gas during the day (during peak electric use elsewhere on the electric grid) and use electricity at night (during off-peak electric use elsewhere on the electric grid). The Advanced Hydrographs provided by the National Weather Service document small floods occur over a 1-2 week period; whereas, moderate or major floods occur over a 30 to 60 day or more period for a given location. In the Lower Mississippi River water could be withdrawn over several months in the spring and summer every year. Thus, the pumps would have to move the water from the interim retention ponds into the pipelines/aqueducts for a likewise duration depending on the severity of the flood event. The capture pipes and the retention ponds and transport aqueducts are expected for use seasonally estimated during February to October. The modified levees and the pipes and should have man-way and large equipment access to enable entry for maintenance and for debris/sediment removal during the off-season. An additional use of the NSWG is to provide for groundwater aquifer recharge along the transportation routes. Vertical shafts drilled into the ground adjacent to the aqueducts could be used to gravity feed some water from the aqueducts to help recharge and sustain groundwater where needed. Experts associated with the Ground Water Protection Council strongly encourage this concept. CONTACT RONALD A. BEAULIEU in Las Vegas, NV for more info.
