Common practice in the United States has been to allow surface runoff
from irrigation systems to leave the farm and return to the canal system
or natural stream. Currently, however, because of increased water
demand, the trend is to collect and reuse this runoff water. Reuse of collected
runoff water increases overall farm irrigation efficiency and decreases
the total amount of water that needs to be pumped or delivered to
the farm. Pollution of natural streams is reduced by stopping the flow of
silt and nutrients that may be contained in surface runoff water. Other benefits
such as reducing drainage costs and improved weed control accrue
from multiple use of return systems. These systems are readily adapted
to automation, and automated or semiautomated pumping stations can be
used advantageously in many return flow systems

Bondurant, J.A.

USDA - ARS - NWISRL

Dokumentation 1Berichte-Reports-RapportsSektion 1, 1- 4Automated pumping station for reuse of irrigation runoff waterJames A. Bondurant "Common practice in the United States has been to allow surface run-off from irrigation systems to leave the farm and return to the canal sys-tem or natural stream. Currently, however, because of increased waterdemand, the trend is to collect and reuse this runoff water. Reuse of col-lected runoff water increases overall farm irrigation efficiency and de-creases the total amount of water that needs to be pumped or delivered tothe farm. Pollution of natural streams is reduced by stopping the flow ofsilt and nutrients that may be contained in surface runoff water. Other ben-efits such as reducing drainage costs and improved weed control accruefrom multiple use of return systems. These systems are readily adaptedto automation, and automated or semiautomated pumping stations can beused advantageously in many return flow systems.Operating Principles for Reuse of Water; The return flow system collects the runoff water from one or morefields and returns it to the point on the farm where it may be used effec-tively and efficiently. This water may be:(1) returned to the same field that is generating runoff, (2) applied to higherlying fields, or (3) applied to a lower lying field. A reservoir large enoughto store the runoff from two or more irrigation sets is required if the col-lected runoff water is handled as a separate supply. This water can then bepumped for a given irrigation set and may be used on either higher or lowerlying fields. Automatic control of these larger storage systems utilizes wa-ter level sensing devices,Automatically cycled pumping stations, controlled by water levelsensing, are used if the runoff water is returned immediately as it occurs.1/Contribution from the Northwest Branch, Soil and Water ConservationResearch Division, Agricultural Research Service, USDA; Idaho Agri-cultural Experiment Station cooperating.1) Agricultural Engineer, Snake River Conservation Research Center,Kimberly, Idaho 83341.139These systems return the runoff water to either the set generating the run-- • off or to another area and require very little reservoir capacity.An efficient method of using the collected runoff water for surf iceirrigation systems is by pumping it to provide a cutback stream (I). Todo this, water from the return system is used to supplement the originalsupply while water is advancing to the end of the irrigation furrow. Whenrunoff begins, pumping from the collected supply is stopped. This resultsin a high initial or primary flow followed by a reduced or cutback second-ary flow in each furrow. This system can be manually started and thelength of pumping time controlled by a time clock. Fully automatic opera-tion is possible if the irrigation water distribution to the field is also fullyautomatic. Smaller pumping equipment and reservoirs are required forthis system than for most other reuse systems. Using the return systemin this manner can result in higher surface irrigation efficiencies than arenormally obtained.Pumping Station Pumping stations for return flow systems consist of the collection. eservoir, pump sump, pump and controls, and the pipeline to return thewater to the irrigation system. The collecting reservoir can serve as thepump sump or a separate sump can be used. The size of the sump dependsupon the method of handling the collected water. Large sumps are madewith heavy construction equipment, while small sumps can be made with atractor-mounted backhoe. The inflow should be piped into the sump and thesump itself diked to prevent erosion by inflowing water. The pump stand isusually made of either concrete pipe, block, or a supporting structuralframe. Small sumps can be made entirely from precast concrete pipe sec-tions or precast concrete tanks, The sump design requirements for effi-cient intake conditions are given by Shahroody and Davis (3).The suction side of the pumping station consists of a strainer, footvalve and the suction pipe. The discharge side will have a valve and aneasily disconnected section so that the pump may be removed without emp-tying the pipeline. Priming is not a problem with these pumping stations.Where the runoff water is returned to a higher elevation, the pipeline isfull of water, thus creating back pressure on the foot valve and supplying acontinuous prime to the pump. Incoming water to the pump sump may needto be screened to remove debris too large to pass through the pump.'ControlsAutomatic controls for return systems are generally of two types -water level sensing controls or time controls. Water level sensing controlsare either float-operated switches or electrical sensors which use the wa-ter as a conductor in the circuit. These water level sensing systems oper-ate by starting the pump at high water level and stopping it again after thewater level is lowered. The float-operated control system usually consistsof a float which slides through a control sleeve on a rod. The pump is turnedon by a switch when the float reaches the high level and is turned off by theNumbers in parentheses refer to appended references.140same mechanism when the float reaches the lower level. Adjustable upperand lower stops on the float rod are used to set the "on" and "off" levels.These stops operate mechanical or magnetic switches which start and stopthe pump motor. If the motor is larger than about 2 hp, the switch is usedto operate the larger magnetic starter. Float-operated controls some-times give trouble because the float may bind in the slide mechanism, orthe mechanically operated switch may not always work. Problems with themechanical switch can be overcome by using a tilting mercury switchturned on and off by the float rod. Mercury power relays are more reliablethan mechanical relays for controlling motors or operating magnetic start-ers. These float-operated systems can also be run with a cable mechanismto eliminate binding of the float rod in the slide assembly. A simple floatswitch setup is shown in Figure 1 a. A diagram of the magnetic switch isshown in Figure 1 b.Electrode-operated controls utilize two electrodes in a conductivecircuit with water serving as the conductive medium. A low resistancecircuit is energized when the water level rises to the upper electrodewhich controls the "on" pump position. As the water level drops below theupper electrode, a higher resistance circuit, making contact through thewater and the suction pipe, keeps the control circuit energized. When thewater level falls below the lower electrode, the holding circuit is de-ener-gized and pumping stops until the water level rises again to the upper elec-trode. The sensing electrodes may be either solid electrodes, Figure 1 d,or small contacts mounted on insulated electrical conductors, Figure 1 c.The electrodes must be located in the pump sump so that they are pro-tected from inflowing water splash, which can cause premature operation.The electrode control is also commercially available with a solid switchin which the switching is accomplished with a silicon controlled rectifiercircuit rather than an energized relay circuit, Figure 1 d. An electrode -controlled system is shown in Figure 2.Both the float-operated control and the electrode control can be usedto start pump operation at a lower limit rather than an upper limit. Inthese systems the runoff water is pumped to keep a set water level in anelevated reservoir. The control signal in this case is transmitted to thepumping station either by wire or by radio. Pressure-operated switches,similar to those used in many domestic water systems in the United Statescan also be used in this system. The pressure controls have adjustabletension contacts which can be set for a given pressure differential, thusturning the pump on when the water level in the upper reservoir falls to apreset level.Automatic control of return system pumping stations also can be ob-tained with timing clocks or a timing clock in conjunction with a runoffflow sensor. Return systems using runoff water to obtain cutback streamscan be automated in this manner if they are used with an automated deliv-ery system (2). Clock timed delivery systems are most adaptable, sincerunoff pumping can be synchronized without signal transfer from the deify-ery system.Automatic pumping stations using internal combustion engines as a141power source can be operated with virtually the same type of water level'sensing equipment. In this case the control signal operates a relay which,in turn, energizes the starting system on the engine. Protective devicesfor sensing loss of oil pressure, high engine temperature, loss of prime,etc., are required on these installations.Semiautomated pumping stations are started manually and are oper-ated through a timeclock which stops the pumping at the desired time.References1, Bondurant, J.A. Design of recirculating irrigation systems. Acceptedfor publication, Trans. Agr. Engr. 	 1969.2. Humpherys, A. S. and J.A. Bondurant. The development of automaticirrigation structures and devices. 1966 reports, Hawaiian Sugar Tech-nologists 25 th Annual Meeting, Honolulu, Hawaii, November 1966.Shahroody, A. M. and J. R. Davis. Efficiency of pumping from smallcircular sumps. J. Irrig. and Drainage Dir. , ASCE 90:(IR I), paper3817, p. 1-8, March 1964.Figure 1. Water level sensing controls for automatic irrigation runoff re-turn systems. (a) Float operated mechanical switch. (b) Dia-,—ccram of magnetically operated reed switch showing, 1) a magnetic float.d 2) the magnetic reed switch. (c) Cutaway of a sensing electrode. (d),id state switch with solid upper and lower sensing electrodes.142Figure 2. Automatic return system controlled by an electrode water levelsensing device. The technician is holding the electrode.143

Automated Pumping Station for Reuse of Irrigation Runoff Water

Northwest Irrigation & Soils Research Laboratory Publications

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Automated Pumping Station for Reuse of Irrigation Runoff Water

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