tion and government programs. Statis- tical analysis of cotton revenue over time reveals price variability to be the Vertical may improve primary source of income risk, while yield variability contributed very little salinity and moisture to income risk. The proper choice of risk-management tools then targets price risk rather than yield risk. The Abdul Karim Yusufzai D Mark E. Grismer two tools that focus on price risk are hedging and forward contracting. The survey results show that 25% of cotton growers use hedging as a risk-man- Existing drainage systems in lateral drainage systems may be exac- agement tool, while only 1.6%report many clay fields of the Imperial erbated by shallow fine-sand , using crop insurance. This illustrates Valley have failed to improve soil which are a source of artesian water that producers make appropriate salinity and to provide moisture into the clay. Lateral drainage systems choices among risk-management tools conditions favorable to crop were not designed for these condi- when the source of risk has been iden- growth. In some fields, these tions, although several drainage stud- tified and several risk-management al- problems are exacerbated by ies from the 1940s and 1950s describe ternatives exist. the widespread occurrence of the fine- saline artesian water from a sand . This artesian water re- shallow sand aquifer. This pilot- Awareness increasing sults in relatively high soil moisture in Awareness of risk issues is increas- scale field study in the Imperial the clay soil profile, and in progressive ing among California producers. Al- Valley indicates that vertical salinization of the root zone. though producers regard many drainage is more effective than Although they have been only sources of risk as relevant, it appears traditional tile systems in briefly considered as an alternative in from their responses that the attention reducing artesian water levels and the Imperial Valley, vertical drainage of lenders is making financial risk the overlying clay soil moisture, systems have been successfully in- paramount among the current risk and should over time also reduce stalled in other semiarid to arid re- concerns. The tools available to pro- the salinity of these . The gions such as the Patterson area of ducers to help manage particular risk cost of a widely spaced drainage Stanislaus County, the Salt River Val- sources vary in their effectiveness and system appears comparable ley of Arizona, and parts of the Red availability, and therefore in popular- to “splitting” existing drainlines. River Valley of North Dakota. This re- ity of use. Many producers indicated port evaluates the potential for and that they would be interested in using Drainage systems are commonly used feasibility of developing a shallow ver- some of the less available tools, such in arid irrigated regions to promote tical or system for the as hedging and crop insurance, if the crop growth by controlling water-table clay soils overlying fine-sand aquifers tools were available for their crop or depth, root zone salinity and soil aera- in the Imperial Valley as a means of livestock enterprise. This indicates la- tion. The Imperial Valley is extensively reclaiming or improving these soils for tent demand for these tools. drained with both open and crop production. We also compare the The limited availability of effective lateral (tile) drainage systems that are costs associated with lateral and well risk-management tools severely limits designed to provide relief from shal- drainage systems and consider some many producers’ ability to mitigate low water tables. As a result of low of the benefits and drawbacks associ- risk. At a time when California pro- permeability, the lateral drainage sys- ated with each system. ducers as a whole are becoming more tems are relatively ineffective in many aware of risk concerns, this shortage of the heavy clay soils that make up Imperial Valley setting poses obstacles to risk management. over 40% of the irrigated valley (Cali- The Imperial Valley is a highly Until tools like crop insurance and fu- fornia , May-June 1988). Im- stratified alluvial valley with an arid tures markets are better tailored to the proving such drainage systems may be climate characterized by an average needs of producers in California, and unfeasible because of the high costs as- annual rainfall of approximately 3 until producers become better in- sociated with narrowly spaced inches, high summer temperatures, formed about managing income risk, drainlines. Nevertheless, during the low relative humidity and abundant the state’s agricultural sector will face past 3 decades growers in parts of the sunshine. The near-surface layers to unnecessarily high levels of financial valley have ”split” the original drain depths of 300 feet alternate between stress. spacing in the clay soils in an effort to sands, silts and clays that interfinger improve their efficacy, with little and are cross-bedded in formation. S.C. Blank is Extension Economist and 1. documentation that any improvement Soil boring by the USGS near the city McDonald is Research Assistant, Depart- was achieved. of El Centro indicates that the silty ment ofAgricultura1 Economics, UC In our previous work in the area, clay and clay surface soils of the area Davis. we found that the poor performance of are underlain by sands at depths rang-

12 CALIFORNIA AGRICULTURE, VOLUME 49, NUMBER 2 ing from 13 to 55 feet of land surface and thicknesses of no more than 180 feet. Development of this sand aquifer as a potential domestic or industrial source of water is limited by the rela- tively high salinity of the (5 to 10 times that of available Colo- rado River water) and the lack of need for additional water supplies. How- ever, it was found that the transmissi- bility of the sand aquifer is moderately high, on the order of 100 to 10,000 gal- lons per day per foot (gpd/ft), and that production could easily yield in excess of 100 gallons per minute (gpm). Similarly, in a detailed study at the UC Desert Research and Extension Center (DREC),referred to locally as the Meloland area, we found a fine-sand aquifer underlying the clay soil at depths of less than 6 feet of land surface, with a thickness in excess of 20 feet and a transmissibility of roughly 1,500 gpd/ft. The salinity of the shallow groundwater ranged from 5 to 6 dS/m (decisiemens per meter equivalent to the old unit of millimhos per centimeter). In both cases the transmissibility of the sand aquifer, although not excep- tionally large, is sufficient to develop vertical drainage systems. However, the groundwater quality is relatively poor. With careful management this groundwater could be applied to salt- tolerant crops, or blended with Colo- In many clay fields of the Imperial Valley, vertical drainage systems may be more effec- rado River water, but eventually the tive than existing lateral drainage systems. This pilot vertical drainage system was less expensive to install and its net annual cost was comparable to traditional pumped groundwater would require systems. disposal via the surface drainage ca- nals to the Salton Sea. which to compare the performance of From the salinity control perspec- This study was prompted in part by different vertical and lateral drainage tive, it is appropriate to gauge the per- the fact that in a clay field systems. formance of the drainage system in (area 70 of the UC DREC) has re- terms of the efficiency with which the mained practically invariant over the Drainage system Performance system extracts root zone drainage, past 30 years of record despite con- The design objective of both lateral where root zone drainage is that frac- tinuous lateral drainage at a depth of 6 and vertical drainage systems is to im- tion of the applied water not used by feet and several leaching studies in- prove root-zone soil aeration and salin- the crop or lost by evaporation. This volving continuous and intermittent ity through control of the water-table efficiency depends on several factors ponding and excess . The depth in the soil. The performance of related to the hydrogeologic setting of soil profile salinity reaches a maxi- these systems is typically evaluated in a lateral drainage system, such as mum value at a depth of roughly 5 terms of the extent to which control of drain depth and spacing, soil perme- feet, corresponding to the pressure the at a desirable depth for ability and aquifer depth. The drain- head (water elevation) of the artesian crop production is achieved. Unfortu- age efficiency of lateral drainage sys- aquifer. Because we had a consider- nately, the criterion of water-table tems can be very low, with the larger able data set for this site and we found depth may not adequately describe the fraction of the root zone drainage by- it to be representative of many areas in performance of the drainage system in passing the drainlines. In a vertical the valley, we used the characteristics terms of salinity control (Culiforniu Ag- drainage system, the extraction wells of this site as our base conditions with riculture, November-December 1990). control the shallow groundwater sys-

CALIFORNIA AGRICULTURE, MARCH-APRIL 1995 13 tem in such a fashion as to capture the Although similar in concept to the creasing spacing, and the design prob- root zone drainage, as well as some re- lateral system design, vertical or well lem becomes one of selecting a system gional groundwater flows. Despite the drainage-system design involves more with adequate performance in terms of differences in performance, both lat- complex equations or computer mod- water table and salinity control for the eral and vertical drainage systems de- eling and the choice of either different least cost. sign involves the use of basic ground- well-field layout patterns of a simple water flow equations to determine the grid or the more efficient triangular Comparison of costs minimum spacing of drain lines or pattern, which is potentially more dif- The costs of a relief, or lateral, drainage wells necessary to maintain ficult to install. Because of the variable drainage system are primarily associ- the water table at a desirable depth thickness and large area of the shal- ated with installation of the drainlines while capturing root zone drainage. low, fine-sand aquifer in the Imperial and the number of control structures, Assuming the soil profile character- Valley, we chose a vertical drainage such as manholes and sumps. For a 1- istics of the UC DREC site as represen- system design based on the ”skim- square-mile field, the least expensive tative of a 640-acre (1 square mile) ming well” concept used on islands lateral drain layout includes a series of field, we determined lateral and verti- for the extraction of fresh water above parallel collector lines, at an appropri- cal drain spacings from applicable sea water, in a triangular pattern lay- ate spacing, draining into submains spacing formulae and groundwater out. This design involves a number of that drain into a telescoping collector flow models, respectively. Taking the relatively shallow wells connected by drain that increases in diameter as the design water-table depth of at least 4 a disposal pipe network, as compared number of submains draining into it feet and a lateral depth of 6 feet, and to the more widely spaced individual increases. Control structures for main- ignoring upward flow to the drain- high-production wells commonly used tenance are often located at the junc- lines from the artesian aquifer, lateral for vertical drainage. Based on com- tion of the submain and collector drain spacings from the formulae of puter simulation studies for the fine- drains. The collector drain flows enter Donnan, Hooghoudt and Ernst sand aquifer at the UC DREC, the pos- drain sumps, eventually discharging yielded lateral spacings of 40 to 160 sible well spacings ranged from 600 to into district drainage canals. For the feet. The Imperial District 1,400 feet at well depths of less than 50 purposes of this analysis, we obtained has historically recommended a lateral feet and flow rates of up to 250 gpm 1992 cost figures from local contractors spacing of approximately 100 feet for per well. and from the Imperial Irrigation Dis- valley soils, but has more recently sug- In both the lateral and vertical drain trict. Table 1 summarizes costs for the gested that a .%%foot lateral spacing for scenarios, the costs associated with lateral drainage system with a 68-foot the clay soils would be more effective. system installation increase with de- spacing, and figure 1 illustrates how drainage system costs depend on drain spacing. The costs of the well drainage sys- tems are primarily associated with the pump and well installation, the pipe network necessary to remove pumped drainage from the field and the energy costs associated with pumping. The well field layout is in a triangular pat- tern in the 1-square-mile field, with rows of individual wells that either discharge into a PVC collection pipe that eventually enters a mainline pipe discharging to a district canal, or dis- charge directly to a canal from the field. Each well would be pumped by a dedicated submersible pump in or- der to minimize maintenance prob- lems and surface obstructions. Because there is only limited well drilling in the Imperial Valley and local contrac- tors don’t exist, we used well drilling cost figures from contractors in Yo10 County and parts of the San Joaquin Valley. We assumed that if drainage well installation projects were to de- velop in the Imperial Valley, a drilling

14 CALIFORNIA AGRICULTURE, VOLUME 49, NUMBER 2 contractor business would be estab- ence in performance of the two types eter wells and shallow depths. How- lished, with rates similar to those in of system may be the deciding factor. ever, the system performance exceeds other alluvial valleys. Moreover, we It should be noted that these cost that of the existing lateral drainage found that after penetrating the clay comparisons assume that the grower system (initially installed in 1963 and layer, a simple tractor-mounted spray would obtain external financing for replaced in 1988) in terms of reducing jet nozzle was adequate to install the the drainage project. Use of internal soil moisture in the clay and, in due wells. We also noted that the rather funds would require a smaller rate of time, the soil salinity. The primary shallow depths of the proposed well return, which would favor the lateral drawbacks of the pilot-scale system, or systems may allow more rapid instal- drainage systems. of any of the proposed vertical drain- lation, by drive-point methods or by a age systems, are the need for electrical modified jetting apparatus, at much Vertical drainage systems power in the field and the land re- lower costs than are assumed here. In order to evaluate the practicality quired for the wells and disposal pipe Typically, as the well spacing in- of vertical drainage, and in an effort to network. These inconveniences can be creases a greater pumping rate (gpm) improve soil moisture and salinity reduced by selecting the largest well is required to maintain the minimum conditions in the clay soils at the UC spacing appropriate for the water-table depth. Table 2 summarizes DREC, we installed a pilot-scale drain- hydrogeologic conditions of the field costs for the vertical drainage system age well system in area 70 to evaluate and by burying the disposal pipe and with a 985-foot spacing, and figure 2 vertical drainage feasibility in the wiring network in the field. In addi- illustrates how vertical drainage sys- field. The well system consists of eight tion, the vertical drainage system tem costs depend on well spacing. 2-inch-diameter wells skimming water would require regular maintenance The drainage system costs shown in at depths of 15 to 18 feet and pumping that the lateral systems do not require. figures 1 and 2 indicate that the verti- at a rate of 1 to 2 gpm per well. The cal drainage system costs are less than well field has lowered the artesian wa- Summary and conclusions those of lateral drainage systems for ter level below the clay soil to dis- In many clay fields of the Imperial drainline spacings less than approxi- tances in excess of 120 feet away, as Valley, vertical drainage systems may mately 65 feet (the maximum recom- well as reducing soil moisture in the be more effective than existing lateral mended spacing for clay soils). The clay. The system is roughly equivalent drainage systems. We evaluated the primary difference between the two to a single 6-inch-diameter well pump- economic feasibility of the vertical sys- types of systems in terms of annual ing at 10 to 15 gpm and draining 3 to 4 tems by comparing their costs with costs is that the vertical system is con- acres of land. As a result of increased those of the lateral systems. Based on siderably less expensive to install but water movement through the clay, we projected costs for both drainage sys- has greater operating costs associated anticipate reduction in soil salinity. So tems at installation, vertical drainage with energy (electrical power) and far, after 12 months of continuous systems are much less expensive to in- maintenance. From the initial invest- pumping, small declines in salinity stall and have a net annual cost that is ment perspective, the vertical drainage have been observed. After some diffi- comparable to that of the traditional system is competitive; however, in culties associated with the initial in- tile drainage systems. Computer simu- many fields of the valley, lateral drain- stallation of the well system, the sys- lation and pilot-scale field studies in- age systems already exist and the cost tem has operated smoothly with only dicate that the vertical drainage sys- of "splitting" the existing drainlines regular maintenance (2 hours) of the tem is more effective than the would be similar to that of installing pump and fittings every 6 weeks. Such traditional tile systems in reducing ar- drainlines at the l26-foot spacing, or maintenance would not be required tesian water levels and the overlying approximately $95 per acre. At this for the submersible pumps used in the clay soil moisture, and should over cost, only the most widely spaced well cost estimates given here. time also reduce the salinity of these system (1,400-foot spacing and 50-foot The limitations of the pilot-scale soils. Finally, it appears that a widely depth) may be competitive. The differ- system are the relatively small-diam- spaced drainage well system is similar in cost to "splitting" the existing drainlines, and if a groundwater drill- z280- ing business is established in the Im- perial Valley, vertical drainage may become a cost-effective and desirable alternative for improving saline clay soils in the valley. 5 160- 140- 120- A. K. Yusufzai is Associate Engineering ;100- Geologist, Regional Water Quality Con- 280 IIIIIIIIII 30 40 50 60 70 60 90 100 110 I20 130 600 700 800 9w 1,o001,1001,200 1.3001,4w1,500 trol Board, Sun Francisco Bay Region and Drsinllne spacing (bet) Well spacing (feet) M. E. Grismer is Associate Professor, Hy- Fig. 1. Lateral drainage system costs Fig. 2. Vertical drainage system costs drologic Science, UC Davis.

CALIFORNIA AGRICULTURE, MARCH-APRIL 1995 15