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Method to improve water resourcesmanagement in groundwater pumpingareas and a case studySevero de la Cruz a & Efren Peña ba Comisión National del Agua, Av. La República 157, Col.Tabacalera, 06030, Mexico, DFb Research Scientist, Instituto Mexicano de Tecnología del Agua,Apdo P. 235, Civac, Morelos, MexicoPublished online: 02 May 2007.

To cite this article: Severo de la Cruz & Efren Pea (1994) Method to improve water resourcesmanagement in groundwater pumping areas and a case study, International Journal of WaterResources Development, 10:3, 329-337, DOI: 10.1080/07900629408722633

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Water Resources Development, Vol. 10, No. 3, 1994 329

Method to Improve Water Resources Management inGroundwater Pumping Areas and a Case Study

SEVERO DE LA CRUZ1 & EFREN PENA2

1Comisión National del Agua, Av. La República 157, Col. Tabacalera, 06030 Mexico, DF;2Research Scientist, Instituto Mexicano de Tecnología del Agua, Apdo P. 235, Civac, Morelos,Mexico

ABSTRACT This paper describes the methodology used to obtain and analyse infor-mation concerning the operating conditions of wells, pumping equipment and irrigationsystems to develop a sustainable groundwater management programme. A case study isprovided to exemplify how the method was applied to attain a balance between theabstraction of groundwater for irrigation and the natural recharge of the aquifer.

Introduction

Water resources development for irrigation in groundwater pumping areas,without long-term planning in the main aquifers of Mexico, has been responsiblefor the drawdown seen over the last 20 years. Low-efficiency pumping equip-ment, inefficient water use in irrigation systems and the high cost of power havecombined with the drawdown to produce rising production costs and fallingreturns for farmers.

The dimensions of this problem can best be shown in the following examples.In the irrigation unit of Costa de Hermosillo, in north-western Mexico, from 1968to 1988 the drawdown registered was 19 m, approximately 0.95 m per year. Innearby zones the fall in the water level was from 5 to 35 m. From 1989 to 1993,some wells were eliminated and others relocated. This action, together with theextraordinarily high rainfall, has resulted in a reduction in the drawdown to0.18 m per year (CNA, 1993).

Altar Pitiquito, one of the irrigation districts where the method proposed inthis study was applied, has reported a drawdown during the last 20 years ofbetween 1 and 22 m, with an average of 1.10 m per year (CNA, 1993).

Valle de Santo Domingo, also in north-western Mexico, has reported anaverage annual fall in the groundwater level over the last five years of 1.5 m.Some 78% of the wells have a static level below sea level.

The problem of drawdown is generalized in Mexico. As such, methods whichcan assist in controlling groundwater abstraction must be found.

Irrigation districts which experiment with aquifer drawdown can usually becharacterized by:(a) pumped volumes in excess of natural aquifer recharge volumes;(b) due to the drawdown, water must be pumped from greater depths generat-

ing a greater demand for electricity;(c) pumping equipment which is often old and electromechanically inefficient;

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330 S. de la Cruz & E. Pena

(d) poorly maintained channels and low-efficiency application systems whichcombine to increase the volume of irrigation water abstracted.

To development a management scheme for sustainable irrigated agriculture, abalance between groundwater recharge and abstraction rates must be obtained.The abstraction rate can be reduced if conveyance and application efficienciescan be improved. The other half of the equation is to estimate the annualrecharge volume, which is in effect the amount of water available for usewithout lowering groundwater levels. Information from previous in-depth stud-ies of the aquifer must be available. Information concerning other developmentfactors must be obtained including area cultivated per well, crop-water require-ments, and increments in pressure required to operate more efficient applicationsystems.

The volumes of water which each district may abstract must also be deter-mined. In Mexico, meetings are held with representatives from the farmingcommunity and from municipal, state and federal governments, the Ministry ofAgriculture and Hydraulic Resources and the National Water Commission toestablish controls over the exploitation of the aquifer and the use of groundwa-ter. The result of these meetings is generally a programme to reduce the volumeof allocated water.

To offset the low volume of water allocated, and low profitability, productioncosts must also be reduced. This can be achieved by improving electromechan-ical efficiencies and lowering electricity bills. Improvements in conveyance andapplication systems would result in lower water demands, which, in conjunctionwith the rehabilitated pumps, could produce important reductions in productioncosts and greater efficiency.

In support of this programme to allocate water to users, the National WaterCommission and the Mexican Institute of Water Technology have developed amethod which provides the information necessary to administer the groundwa-ter resources, to document the performance of wells and irrigation systems, toapply techniques to improve pumping irrigation systems, and to allow for aninformed decision-making process.

The methodology focuses on developing alternatives to improve aquiferexploitation conditions by defining the irrigated surface per well, with a view tobalancing the abstraction with the natural recharge, and improving the efficiencyof water and electricity use to increase cost effectiveness.

Procedure

The study consisted of two parts: evaluation of the electromechanical efficiencyof the pumping system, conveyance and application efficiencies of the pumpedwater, and development and analysis of farm models with different levels ofimprovement of existing equipment and the use of more efficient technology.

Part 1: Evaluation of Efficiencies

This consists of sampling for the evaluation of efficiencies and planning.

Pumping irrigation systems. A systematic sampling method must be used toselect representatives of all existing systems to ensure the validity of the

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Improving Management in Gronndwater Pumping Areas 331

information about the conditions of wells, pumps, irrigation systems, canallinings, and additional information concerning the relative proportion of eachcrop.

Determination of efficiencies. At selected locations, studies of electromechanicalefficiencies of pumping equipment, and water conveyance and applicationefficiencies were carried out with a mobile laboratory. Parameters for wells andpumping equipment included pumping height, voltage, amperage, dischargeand power factor to determine the electromechanical efficiency. Parametersconsidered for conveyance efficiency included discharges to and from canals andpipes to determine efficiency for the various lining materials. Parameters forwater application efficiency and crop requirements included description andproportion of the total crop area, water retention capacity, wilting point of crops,texture, bulk density and moisture content of soil and volumes of water appliedfor each irrigation method (Doorenbos & Pruitt, 1990).

Part 2: Analysis of Farm Models

The models were developed to determine the maximum area each farm may usefor cropping, without exceeding the allocated maximum water volume. Themodels serve to provide the farmers with a guide to the current situation, whichwas unsustainable, and to inform them of the alternatives available to them withthe rehabilitated irrigation equipment.

To develop the basic farm models, the average irrigated area per well for theaquifer, the crops and their proportion of the cultivated area must be considered.

For the model, the following calculations were made for both gravity andpressurized systems:

• net volume of water needed for each crop, after adjusting for the efficiencies,to estimate the gross volumes to pump;

• current net water volumes for cropping areas;• potential cropping areas using authorized pumping volumes;• monthly water volumes required;• number of pumping hours, before and after rehabilitation of pumping equip-

ment;• total power consumption to pump the volume of water for the model, taking

into account the electromechanical efficiencies before and after the rehabili-tation. Application operating pressure must also be considered; and

• cost of the power consumed, in kilowatt-hours per month.

To validate the proposed method, three irrigation units were used. A descriptionis provided of the partial results obtained during the procedure followed at oneof these units.

Case Study

Scope and Origin

In Mexico, 1.94 million hectares are cultivated in 53 345 irrigation units of which47 464 use groundwater. Approximately 7% of all electrical energy produced in

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332 S. de la Cruz & E. Vena

Table 1. Electricity rate table.

Consumption range Rate NPs/kWh

0-5000 0.104965001-15 000 0.12548

15 001-35 000 0.1385035 001 or more 0.15378

Mexico is consumed to pump groundwater for these systems (CNA, 1993). On29 May 1990, government subsidies for electrical power consumption by farmerswere reduced as part of an overall restructuring of the national economy,resulting in a 148% increase in the cost per kWh. The withdrawal of the subsidywas then made progressive. By February 1993, economic stability reduced thecost of generating electricity. These savings were passed on to the consumers,resulting in a continued withdrawal of the subsidy and a reduction in theindexation of the rate for users. In February 1993 the factor was reduced to 1.005.In October 1993, the factor was eliminated and a set rate table was adopted, withincreasing prices for greater consumption, thereby stimulating efficient use. Thisis given in Table 1 (CNA, 1994).

In response to requests from farmers, the federal government created the'Programme for Efficient Use of Water and Electricity' (CNA, 1993) aimed atimproving the efficiency of the farming system and, thus, the profitability. Theprogramme included incentives for capital investments to improve pumpingequipment, canal lining, construction of pressurized irrigation systems and landlevelling. The programme provided three mutually exclusive options:

(1) Farmers with pumping systems operating at less than 40% efficiency re-ceived 50% of the capital expenditure to upgrade their wells and pumpingequipment to a maximum of NPs 100 000 (on 25 May 1994, US$1 = NPs3.37).

(2) Those with greater than 40% efficiency could receive 50% of the costsincurred in the construction of storage reservoirs, land levelling and acqui-sition of pressurized irrigation systems up to NPs 100 000.

(3) Those who wish to improve both pumping and irrigation systems canrequest government assistance for up to 50% of the costs to a maximum ofNPs 150 000.

The proposed methodology was used at Altar Pitquito, Sonora (Figure 1).Farmers in this area complained of serious economic losses owing to the highcosts of water and electricity. Previous hydrological studies of the aquiferindicated an annual natural recharge of 300 million m3, and an average annualdrawdown of 1.10 m resulting from an annual abstraction of approximately 800million m3 (CNA, 1994). The central portion of the aquifer had an annualdrawdown of up to 6 m.

The annual average volume abstracted during the five previous years wasapproximately 800 million m3. A programme to allocate volumes, agreed jointlyby the CNA, users and representatives from municipal, state and federalgovernments at meetings, gradually reduces the abstraction rate from the aquiferfrom 798 million m3 in 1994, to 435 million m3 in 2001 and finally to 301 million

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Improving Management in Groundwater Pumping Areas 333

Table 2. Conveyance efficiencies determined forAltar Pitiquito.

Length Efficiency LossesMaterial and type (m) (%) (lps/km)

Concrete-lined canal 944 90 9.8Earth canal 527 87 16.9Pipe 702 95 4.7

m3 in 2004. The global abstraction rate still exceeds the estimated 300 million m3

received as natural recharge by the aquifer.

Results

Part 1—evaluation of efficiencies:

(a) Eighty-five individual pumping irrigation systems were studied at AltarPitiquito, following the procedure described. Conveyance and irrigationsystem efficiencies are summarized in Tables 2 and 3 (IMTA, 1992).

(b) Under the 'Efficient Use of Water and Power' programme, 251 pumps of the831 wells in operation were rehabilitated. The results are shown in Table 4(CNA, 1993).

Part 2—analysis of farm models:

(a) The Altar Pitiquito area may be characterized by average cropped area of50 ha per well. The main crops were: grapes (32%), wheat (32%), asparagus(8%), cotton (8%), alfalfa (6%), melon and watermelon (6%), olives (6%) andcitrus (2%).

Net volumes were calculated using the Blaney-Criddle method, a com-puter-assisted system developed by the US Soil Conservation Service, todetermine monthly consumptive water use (USDA-SCS, 1987). Planting andharvest dates, and conveyance and application efficiencies were then con-sidered to obtain the gross monthly volumes. Table 5 indicates the results ofthis analysis.

(b) Modelling: models 1 and 2, in which the current operation conditions of theaquifer were used with continued overexploitation, served to demonstrate

Table 3. Irrigation systems efficiencies atAltar Pitiquito.

Irrigation method

FurrowsBordersOverall surface irrigationSprinklerTrickierMicrosprinklerOverall pressurized irrigation

Efficiency (%)

59.256.356.080.686.590.677.0

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334 S. de la Cruz & E. Vena

Table 4. Pump rehabilitation information.

Parameter

Total pumping head (m)Discharge (lps)Pumping volume/hour (m3/h)Electromechanical efficiency %

Rehabilitation

Before

89.044.0

158.432.4

After

91.079.0

284.467.8

the savings that may be achieved in electricity costs alone as a result of therehabilitation of the irrigation system. In models 3 and 4, crops and theirrelative extensions using efficient pumps and application systems within theconstraints of the allocated volumes are proposed. (See Table 6 for detailsconcerning the basic information for the models.)

Model 1. This model considers the present scenario, with an average croppedarea of 50 ha and the same proportions of crops and gravity-flow irrigationsystems (furrows and borders). The current annual pumped volume is806 900 m3, requiring some 5904 hours of pump operation and 606 670 kWh at acost of NPs 84 256. Following the rehabilitation of the pumping equipment, thissame volume was extracted in 2837 hours, requiring 327 996 kWh for a total costof NPs 42 664, with a savings of 50.6%.

Model 2. Here a cropped area of 50 ha, the current proportion of crops and apressurized irrigation system were considered. An annual pumped volume of573 400 m3 was required, consuming 233 074 kWh over 3620 hours. Conversionto a pressurized system provided a saving of 234 000 m3. Improvements in thepumping system and the well resulted in a reduction to 233 074 kWh usedduring 2016 hours at a cost of NPs 32 195. An additional 92 180 kWh were usedto pressurize the application system at 40 m at a cost of NPS 10 497. However,much of this amount is offset by the savings from the reduction in totaloperating time because of lower total volume and greater electromechanicalefficiency. The total consumption was 325 254kWh at an overall cost to theproducer of NPs 42 692.

Table 5. Efficiencies used to calculate gross monthlyvolumes.

Efficiencies (%)

Irrigation method

Conveyance Application TotalGravity 90 60 54Pressurized 95 80 76

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Improving Management in Groundwater Pumping Areas 335

Table 6. Models developed by method proposed.

Model

1. Asreconstructed2. Asreconstructed3. Asreconstructed4. Asreconstructed

Irrigationmethod

Gravity

Pressurized

Gravity

Pressurized

Area(ha)

50

50

30

40

Volume(m3)

807000

573 000

489 000

459 000

CostkWh

606 707326 000326 000325 300367 300200 200262 700260 500

(NPs)

84 25642 66443 05242 69248 50224 6673136031098

Savings

Volume

29.049.439.470.743.163.1

(%)

Energy

49.448.9

42.4

62.8

Model 3. This projection was made by considering a gravity irrigation systemwith an area of only 30 ha. This plot, observing the proportion of crops grownin the area, would require 488 600 m3, a volume close to that allocated under thewatershed management programme. With the equipment in use at present,approximately 3084 hours would be required, consuming 367 336 kWh at a costof NPs 48 502. After the rehabilitation of the equipment, the cost savingsresulting from the reduction to 1718 hours of pump operating time, at a cost ofNPs 24 667 for the 200 180 kWh consumed, would go a long way to making thefarmer's economic survival possible.

Model 4. This model included the operation of a pressurized system, whichwould allow the farmer to crop 40 ha. If the existing equipment is used, 1614hours would be needed to pump the 459 132 m3 required for the crops. Usingrehabilitated equipment and well, 1614 hours would be required to pump thewater at a cost of NPs 22 835, plus the increment required to pressurize for theapplication system at a total of NPs 31 098. A portion of the cost of pressurizingthe application system is offset by the reduction in the total volume pumped andfrom the increased electromechanical efficiency of the pumps.

Discussion

Gravity Irrigation

Gravity flow irrigation of 50 ha requires 807 000 m3 of pumped water. Byreducing the area to 30 ha, 489 000 m3 are required, which is much closer to thegoal of 429 000 m3 by the year 2001.

Before rehabilitation, the capacity of the pumping equipment was 158.4 m3 perhour, requiring 5094 operating hours per year to pump 807 000 m3. Operatingwith an efficiency of 32.4%, the system consumed 118.8 kWh, with a powerproductivity of 1.33 m3/kWh, and a yearly consumption of energy of607 000 kWh, at a cost of NPs 84 256.00.

After upgrading the equipment and reducing the area from 50 to 30 ha, thepumping equipment with a capacity of 284.4 m3 per hour would require 1718hours per year to pump 489 000 m3. Operating at an efficiency of 67.8%,115.5 kWh would be consumed, the productivity of the power would be

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336 S. de la Cruz & E. Pena

Figure 1. Location of study area.

2.46 mVkWh, a yearly energy consumption of 200 000 kWh, at a cost of NPs24 667.00.

The productivity of the well is improved by 85% and, taking in account 30 haof crop area, the reduction in power consumption is projected to be 407 000 kWhper year, thus contributing to annual savings of NPs 59 589.00.

The adjusted area reduces water abstraction by 318 000 m3 per well, saving atotal of 264.3 million m3 at 831 wells, thus reducing the extent of overexploitationof the aquifer. ^

Pressurized Irrigation

In the original farm model of 50 ha, the volume pumped was 573 000 m3,234 000 m3 less than the volume needed to irrigate the same area with a gravitysystem. While this saving is important, this volume is higher than the maximumabstraction allowed.

Improvements in the wells and the pumping equipment provide energysavings, although additional energy is necessary to pressurize the applicationsystems.

For the farm model of 40 ha, the pumping volume is 459 000 m3 per well,348 000 m3 less than in model 2. Under these new conditions, water used isapproximately equal to the permitted volume.

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Improving Management in Groundwater Pumping Areas 337

Conclusions

The following conclusions can be made. The method used at Altar Pitiquito,Sonora, provided information to modify the size of the farms based on themodels proposed, and allowed for the calculation of available groundwater, andsavings in terms of water and energy that may be obtained. This informationwill then be used to plan the rational use of groundwater to obtain sustainabilityand profitability in agriculture with the present crops.

The information may also be used to allocate water volumes in the future andto plan agricultural development better adapted to existing conditions in theaquifer.

References

CNA (1993) Informe Anual del Programa 'Uso Eficiente del Agua y de la Energía Electrica' Internalreport, Comisión Nacional del Agua, México.

CNA (1994) Riego por Bombeo Agrícola, Internal report, Comisión Nacional del Agua, Mexico.Doorenbos, J. & Pruitt, W.O. (1990) Las Necesidades de Agua por los Cultivos, Estudio FAO, Riego y

Drenaje No. 24 (Rome, FAO).IMTA (1992) Determinación de Eficiencias de Funcionamiento de Sistemas de Riego por Bombeo,

internal report, Instituto Mexicano de Tecnología del Agua, México.USDA-SCS (1987) Irrigation, in: National Engineering Handbook, Section 15, Ch. 1: Modified Blaney-

Criddle Consumptive Use (FAO Option) (Washington, DC, USDA-SCS).

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