Texas A&M University

Permanent URI for this communityhttps://hdl.handle.net/10850/532

Browse

Now showing 1 - 20 of 363

An Interindustry Model of El Paso and Hudspeth Counties, Texas
(Texas Water Resources Institute, 1976-04) Adams, J. W.; Jones, L. L.; Beattie, B. R.; Coffman, W. S.
Establishing Crop Acreage Flexibility Restraints for Subregions of the Texas High Plains
(Texas Water Resources Institute, 1977-01) Lacewell, R. D.; Condra, G. D.
Cropping pattern shifts in many aggregate linear programming (LP) models need to be constrained due to institutional, marketing machinery, and price uncertainty factors. The purpose of this study was to estimate constraints which are referred to as flexibility restraints for major crop acreages in subregions of the Texas High Plains for use in a LP model that was developed to derive water and other input demand. Alternative estimating models for establishing acreage flexibility restraints were developed using methodology and model formulation presented in the literature. The results of these models in estimating flexibility restraints were evaluated using statistical measures and subjective analysis. Models which were analyzed ranged from a simple linear regression model in which the current year's acreage is expressed as a function of last year's acreage to a multiple regression model in which economic and climatological variables were considered. The multiple regression model as formulated and estimated did not provide satisfactory results. However, as in many of the earlier studies the simpler models did provide acceptable performance. From among the simpler models one was selected based on statistical measures and a prioria expectations. The model was used to calculate crop acreage flexibility restraints for three subregions of the Texas High Plains.
Influence of Vegetation Management on Yield and Quality Surface Runoff
(Texas Water Resources Institute, 1977-03) Smeins, F. E.
Water requirements for the United States will triple by the year 2000 (Water Resources Council, 19689. In Texas and many western states about 75% of the total water used is from ground water and this source in many areas is rapidly being depleted. To meet future demands water will have to come from other sources (Runkles, 1972). A possible source is increased water yield from watersheds. The quantity and quality of this surface runoff is influenced by many factors which include precipitation pattern, vegetation-type, soil-type and land use. If surface runoff from watersheds is to be a potential water source, the impact of these factors on water quality and yield must be evaluated. Forests, grasslands and shrublands cover vast watersheds in Texas and North America. Many watershed studies have been conducted in forested regions, but rangeland areas have received only limited attention, particularly in Texas. The significance of these latter types cannot be overlooked since 40% of the land surface in the United States and 60% of Texas support this type of vegetation. The major use of rangeland is domestic livestock and wildlife production. The impact of this use on water yield and nutrient and sediment loss from watersheds requires investigation. The influence of various grazing systems and intensities must be determined in order to coordinate ranching practices with increased high quality runoff. The effect of brush control on runoff yield and quality has not been thoroughly investigated. The purpose of this study was to determine the influence of vegetation characteristics, grazing systems and precipitation on surface runoff from rangeland on the Edwards Plateau region of Texas. Water yield, organic-N, N03-N, NH4-N, N02-N, total and ortho-P, Ca, Mg, K, pH, conductivity, total and calcium hardness, turbidity and suspended sediment load were quantitively evaluated. Field sampling was conducted on small-gauged watersheds on the Texas A&M Agricultural Research Station at Sonora, Texas. These gauged watersheds, which have been established over the past 13 years by the Agricultural Research Service (ARS), represent a variety of grazing systems ranging from continuous heavy grazing with poor vegetation cover to fourpasture and seven-pasture deferred rotation systems with good cover. In addition several different techniques have been used for woody plant control on the watersheds. The Sonora Research Station, with over 25 years of grazing management research, provides a unique area for study of the effects of grazing management and brush control on surface runoff, nutrient load and sediment yield.
Select Minerals and Potable Use of Reclaimed Wastewaters
(Texas Water Resources Institute, 1977-03) Wolf, H.
The long-observed relationships of an influence of drinking water mineral content on heart-circulatory deaths are developed to indicate that sodium -- when present in sufficiently high concentrations -- may be detrimental to human health. An hypothesis is presented that suggests that drinking water sodium contributes more to the health effects picture than is ordinarily attributed to this normally minor avenue of ingestion by virtue of its influence on taste behavior. Mechanisms of action for metals as they relate to cancer and for sulfates as they relate to urinary calculi were also observed in the literature.
A Report on the Effectiveness of Texas Water Resources
(Texas Water Resources Institute, 1977-05) Ruesink, L. E.
A readership survey conducted in May 1977 found that readers of Texas Water Resources find it useful, attractive and informative. The bulletin is published by the Texas Water Resources Institute to generate public awareness and understanding of water resources issues. The 31 percent response rate from the survey was evidence that the publication is well received. Results indicate that each copy is read by an average of three individuals. Ninety-eight percent of all responses were in favor of the publication.
Outlook for Energy and Implications for Irrigated Agriculture
(Texas Water Resources Institute, 1977-09) Lacewell, R. D.; Patton, W. P.
Agriculture uses large quantities of energy to pump groundwater for irrigation. This means the cost of energy has important implications for the industry in terms of costs and profitability. Increases in the prices of energy sources such as natural gas, electricity, liquid petroleum gas and diesel can cause economic hardship for irrigators, particularly if those increases are unanticipated. The purpose of this paper is to briefly summarize important trends in the current domestic energy situation that could have significant impacts on the future cost and availability of energy, and to show what the implications of those trends are for irrigated agriculture. The primary focus of this study will be on trends in natural gas, since natural gas is the major fuel used for irrigation in the Great Plains states.
The Impact of Energy Shortage and Cost on Irrigation for the High Plains and Trans Pecos Regions of Texas
(Texas Water Resources Institute, 1978) Petty, J. A.; Zavaleta, L.; Hardin, D. C.; Condra, G. D.; Lacewell, R. D.
The High Plains and Trans Pecos regions of Texas are semi-arid crop production regions located in the western part of the state. Relatively low levels of rainfall are supplemented by irrigation from groundwater supplies. These regions produced 51 percent of the cotton, 42 percent of the grain sorghum, and 48 percent of the wheat produced in Texas in 1974 (Texas Crop and Livestock Reporting Service). Considering only irrigated production these percentages were 75, 85, and 91 percent of Texas irrigated crop production for cotton, grain sorghum and wheat respectively. The importance of the High Plains and Trans Pecos regions to Texas crop production are not limited to these three crops, however, these statistics do serve to illustrate the significance of these regions in the Texas agricultural economy. While it is easily seen that the majority of irrigated production (for the crops mentioned) in Texas occurs in these regions, it should be noted that the importance of irrigation in the High Plains and Trans Pecos regional economies is much greater than these statistics show. On the High Plains 86 percent of the cotton, 90 percent of the grain sorghum, and 75 percent of the wheat produced in 1974 was harvested from irrigated acreage. Rainfall is somewhat less in the Trans Pecos region and 100 percent of the production of these crops was under irrigation (Texas Crop and Livestock Reporting Service). More than 60 percent of the value of agricultural crops in Texas is produced on irrigated land (Knutson, et.al.). Thus, the crop production of these regions is vitally important to the Texas and respective regional economies. Crop yields are heavily dependent on groundwater irrigation and extremely sensitive to any factor which may affect the availability or cost of irrigation water. Availability and price of fuel used in pumping groundwater are the critical factors which directly affect the availability and cost of irrigation water. About 39 percent of the energy used in Texas agriculture in 1973 was utilized in pumping water, compared to 18 percent used in machinery operations. Of this irrigation fuel, 76 percent was natural gas, the majority of which was consumed in the High Plains (Coble and LePori). Current supplies and reserves of natural gas have reached critically low levels in recent years and producers in the High Plains and Trans Pecos regions are faced with possible curtailments of, and certain price increases for their irrigation fuel (Patton and Lacewell). The threat of possible curtailment of fuel supplies during the irrigation season imposes greatly increased risk to irrigated crop production since curtailment of natural gas supplies during a critical water use period would significantly reduce yields (Lacewell). This threat would also increase financial risk and restrict availability of credit. Continued price increases for natural gas will increase costs of pumping irrigation water and hence the costs of irrigated crop production (Patton and Lacewell). The Ogalalla aquifer underlying the High Plains and many of the alluvium aquifers underlying the Trans Pecos are exhaustible; i.e., there is a negligible recharge from percolation and other sources. Therefore, even with unchanged natural gas prices, these groundwater supplies are being "economically" exhausted over time as pumping depth increases. Increases in fuel prices will lead to reduced groundwater pumpage and result in less groundwater being economically recoverable. Although life of the physical supply will be exhausted, a greater quantity of groundwater will be economically unrecoverable for irrigation without significant product price increases.
Institutional Arrangements for Effective Groundwater Management to Halt Land Subsidence
(Texas Water Resources Institute, 1978) Jones, L. L.; Brah, W. L.
In the Upper Galveston Bay region of the Texas coastal zone, water from naturally replenished underground aquifers provides much of the freshwater supply for municipal, industrial and agricultural needs. The availability of these easily accessible low cost freshwater supplies has contributed to the building of a strong and dynamic economic base. However use of these common water supplies in excess of natural replenishment has resulted in a gradual but accelerated and irreversible subsidence of the land surface throughout the region. The cause is long term and due to collective use of groundwater. This natural phenomenon generally exhibits the range of characteristics expected when the carrying capacity of valuable common property resources is exceeded under dynamic socio-economic use pressures. These characteristics include competing and conflicting resource use, externalities (socioeconomic and environmental impacts) and complex social, legal and political dilemmas. Regional use of groundwater in excess of the "safe" production potential of the underground water bearing system has caused physical and economic losses in the coastal areas. Surface subsidence in excess of 8.5 feet has resulted in serious socio-economic and environmental impacts because of the loss of land elevations in already low shoreland areas. Bay waters have permanently inundated previously valuable commercial, industrial, recreational, municipal and private property. Subsidence has increased the susceptibility of much of the region to destruction through tidal surges generated by tropical storms and hurricanes. Conceivably, the somewhat inchoate interests of approximately 350,000 persons and large numbers of state and private enterprises located in susceptible coastal areas are affected. The natural phenomenon of subsidence, and its technical solution decreased groundwater use and/or use of alternative surface water supplies, pose difficult institutional questions and equity issues both to public and private sectors that as yet remain unanswered and unresolved. Traditionally, groundwater has been treated as a free good or at least a relatively cheap one. Since owners of private property overlying the water bearing system are afforded legal proprietary interest in the water in Texas, the regional groundwater resources have been developed and used primarily on an individual, uncoordinated basis with little or no concern for the relationship between extraction and natural replenishment, or regard for any collateral effects of groundwater use. Social costs are unregistered under such an arrangement and only private costs are considered by users. Institutions governing the use and allocation of groundwater resources were primitive or nonexistent. Therefore, effective action to arrest the ever increasing overdraft was absent. With increased water use, however, subsidence related costs have become apparent. For many years the majority of groundwater users ignored the subsidence problem since it was thought to affect and indeed was only felt by a minority of local land owners and waters users bordering on coastal bays and other water courses. Even though the implication (for example, hurricane threat) of subsidence to the region was recognized, an internal cost differential between groundwater and surface water sources hindered voluntary conversion to the higher cost surface water by the collectivity of groundwater users. Aggregate social costs generated by overuse of groundwater exceeded the aggregate price differential, but these social costs were largely unregistered. They were felt only by a minority of community interests in a manner disproportionate to their use of the groundwater. Logically, therefore, intensive use of inexpensive groundwater continued. Although industrial, municipal, agricultural and private interests were interrelated through the common use of the aquifer, a basis for collective action was difficult because of conflicting interests. In the early 1970's a movement began to form some collective organization to soften the conflict and aid individuals to allocate the regional water resources in such a manner as to abate and control surface subsidence; to enable individuals to compete peacefully for scarce resources in a manner that would lead to a satisfactory allocation of currently available or potential supplies of water resources. Water users were thus confronted with the problem of rearranging decision-making capabilities. The execution of a solution was generally beyond individual water user's scope of action due to physical, legal and economic factors. Existing collective organizations and institutions were also viewed as inadequate for this purpose. Water related institutions were vertically and horizontally fragmented, each dealing with some aspect of groundwater use and development but political entities with adequate scope to deal with the problem were either unwilling or unable to engage in regional water management. Indeed, these political organizations and other institutions may have actually contributed to the subsidence problem. They were not only ill equipped to respond, but also were primarily designed for water use, and may have provided incentives to their constituents to continue using groundwater and to generally disregard the overall community interest. Hence, the greater problem in the short run was not one of a shortage of water, but one of creating institutional arrangements to interrelate users of common water supplies and to obtain conjunctive use of surface water with groundwater so that effective management and subsidence control could result. The issues to be addressed were not how shall a resource be allocated among users competing for the inexpensive supply, and the more complex question of how users shall allocate their use of groundwater as against the more expensive surface water. It is an economic dilemma of how best to use existing water supplies and how and when to expand existing water supplies as the demand for water increases. If aggregate demand for water were not met, pressure would be brought to bear upon "scarce" groundwater resources, exacerbating the subsidence of the land. A management institution was needed to devise an acceptable decision system to reorder incentives for groundwater use into disincentives and to reorder disincentives for surface water into incentives. In short, legal, physical and economic relationships between the community of interests embedded in existing institutional arrangements needed to be redefined and restructured. This implied a progressive departure from the traditional way of allocating groundwater resources. Much time, energy and resources was spent by the local community in deciding upon an optimal institutional strategy and devising self-governing organizational arrangements to express their interests and solve their problems. However, the community was hampered in its efforts by obstructions imposed by existing institutional arrangements and by a change resistant political climate of the State Legislature whose authorization for local proposals for an instititutional solution was needed. The political mechanism attained by the community through concerted effort was a special purpose subsidence control district which could respond to the threatening problem only in a limited fashion. The emphasis was on subsidence control through well spacing, regulation and permits, rather than on a more comprehensive approach of integrated and coordinated conjunctive water resource management. Such a district is able only to force important management issues and problems onto other political entities, and must leave many equity issues and needs unresolved and unanswered. It is the purpose of this report to evaluate alternative political structures for comprehensive management of the subsidence area's complex water problems. Alternative arrangements of legal, economic and political institutions with the capacity and ability to conjunctively manage regional ground and surface water resources to abate and control subsidence are developed and examined. These alternative institutional arrangements are based on both practical and theoretical management methods advanced in the literature on water resource management for solving commonality problems in the use of groundwater resources.
Silvicultural Activities in Relation to Water Quality in Texas: An Assesment of Potential Problems and Solutions
(Texas Water Resources Institute, 1978-02-01) DeHaven, M. G.; Blume, T. A.; Jackson, B. D.; deSteiguer, J. E.; Hickman, C. A.; Blackburn, W. H.
Southern forests are expected to supply a large portion of the Nation's future timber requirement. Projected demands on southern forests continue to exceed allowable cut. As an outgrowth of this demand, intensive management of pine forests enabled the South to produce 45 percent of the Nation's timber harvest in 1970 (USDA, Forest Service, 1973). The Southern Forest Resource Analysis Committee (1969) stated that, if projected timber needs of the year 2000 are to be met, at least ten million acres of bare or poorly stocked land must be planted with pine by 1985 and another twenty million acres converted from low-grade hardwoods to pine. The challenge facing forestry in the South is how to meet this increased demand and maintain an acceptable forest environment in the face of increased taxes, rising labor and equipment costs and predicted petroleum shortages. Undisturbed forests are generally recognized as primary sources of high quality water. Although the Federal Water Pollution Control Act Amendments of 1972 (Public Law No. 92-500) make pollution from forest practices increasingly more important, the effects of these practices on water quality are not known for East Texas. The quality of streamflow from forested watersheds fluctuates constantly in response to natural stress, and can be influenced greatly by man's activities. Forest management practices can potentially influence the following water quality parameters: (1) sediment, (2) nutrients, (3) temperature, (4) dissolved oxygen/organic matter, and (5) introduced chemicals. It must be realized from the onset that sediment due to geologic erosion is a natural component of fresh water streams and that high concentrations may have occurred naturally for short periods due to perturbations in the ecosystem such as wildfires. Sediment is not necessarily a pollutant and only becomes one when it can be demonstrated that it is exceeding natural levels and is interfering with the beneficial use of water. A certain amount of sediment and nutrients are needed in Gulf Bays and Estuaries to maintain their productivity (Mathewson and Minter, 1976; Diener, 1964; Ketchum, 1967). Texas does not have a stream water quality standard for sediment and due to the complexities involved will probably not develop one. Thus, sediment as used in this report, becomes important: (1) as a carrier of plant nutrients and forest chemicals, and (2) in that practices which reduce sediment loss will usually reduce nutrient, organic matter and introduced chemical losses and prevent water temperature increases, as well. This report is the result of an interagency contract between Texas Department of Water Resources, Texas Agricultural Experiment Station and Texas Water Resources Institute to: (1) develop an overview of commercial forests and forestry operations in Texas, (2) identify, describe and characterize control strategies for nonpoint sources of pollution from silvicultural activities, and (3) develop and demonstrate a methodology for selecting control strategies in given problem situations. The following topics are covered: (1) an overview of forestry in East Texas, (2) silvicultural practices and nonpoint sources of pollution, (3) control strategies, (4) methodology for the selection of control strategies, (5) institutional aspects of controlling silvicultural nonpoint source pollution, (6) ongoing research and research needs, and (7) hydrology of East Texas. It is important to recognize that this report does not specify that nonpoint pollution from forestlands in East Texas is a problem. Likewise, the report does not set pollution control goals or criteria that should be met by a control plan, since this is the responsibility of the State. In areas where a potential nonpoint pollution problem exists; the suggested control strategies should be useful in selecting control measures that are appropriate to the special conditions imposed by differences in climate, soil, topography, and forest practice.
Economic Impacts of Controlling Soil-Loss from Silviculture Activities: A Case STudy of Cherokee County, Texas
(Texas Water Resources Institute, 1978-03-01) Jackson, B. D.; Hickman, C. A.
Section 208 of the 1972 Amendments to the Federal Water Pollution Control Act (Public Law 92-500) requires the states to develop plans which: (1) contain processes to identify nonpoint sources of pollution, and (2) set forth procedures and methods to control such sources of pollution to the extent feasible. Among the land use activities which are explicitly identified within Section 208 as potential sources of nonpoint pollution problems is silviculture. Texas, since it contains an estimated 12.5 million acres of commercial forest land (Murphy, 1976), has for some time been actively involved in developing the required planning procedures and materials. This document represents one component of this overall planning process. The "extent feasible" clause of Section 208 can be interpreted as recognizing the need to consider economic tradeoffs in reaching a decision as to what level of control, if any, should be exercised to limit nonpoint source pollution from whatever type of activity. This would seem to be a reasonable interpretation since it would be illogical to envision extending controls to the point that their marginal costs would exceed their marginal benefits. Broadly conceived, the purpose of this investigation has been to make a first approximation of the economic tradeoffs that would be associated with any effort to limit the extent of nonpoint pollution resulting from silvicultural activities in Texas. More specifically the study has sought to achieve the following objectives: 1. To develop a methodology For assessing the economic impacts associated with imposing alternative silvicultural nonpoint source controls at varying intensities. 2. To demonstrate how the methodology could be applied to a specific study area to facilitate decision-making about the economic rationality of imposing controls. As the study plan for this project was developed, choices had to be made regarding the range of potential pollutants to consider, the range of alternative control techniques to consider, and the range of economic impacts to consider. Since the nature of these choices represent limitations on the scope of the project, they should be made explicit from the outset. As regards the range of potential pollutants considered, it is recognized that silvicultural nonpoint source pollution can conceivably assume a variety of forms -- nutrients, chemical, thermal, and so on. Nonetheless, in this investigation sediment is the only potential silvicultural pollutant which has been addressed -- and this only indirectly.1 The focal point of the analysis is on the economic impacts of restricting soil loss (i.e. sheet and rill erosion) which is not directly equivalent to sediment yield. Conversion of soil loss figures to sediment yield figures requires knowledge of an appropriate sediment delivery ratio. While this might appear to be a significant limitation of the study, the investigators are of the opinion that it is not. This conclusion rests upon essentially two facts. First, the bulk of the available evidence pertaining to the potential impacts of silvicultural activities on water quality indicates that in those instances where such activities appear to be creating a problem sediment is generally the potential pollutant of greatest importance. Secondly, sediment yields will bear a constant proportional relationship to soil loss. Indeed, if the study unit used in this investigation had been a physical watershed instead of a county, the analysis could have dealt directly with sediment yields rather than soil loss.2 In turn, if actual sediment yields had been estimated, other potential pollutants could have been introduced into the analysis, if so desired, by the use of appropriate loading functions. As regards the range of alternative control techniques that might conceivably be used to limit silvicultural nonpoint source pollution, this investigation specifically considers four possibilities. These are: (1) a countywide limit on allowable soil loss, (2) a per acre limit on allowable soil loss, (3) a tax on excess soil loss, and (4) a subsidy for reduced soil loss. While other policy choices undoubtedly exist, these four alternatives are felt to encompass a fairly broad range of possibilities. Accordingly, this limitation on the scope of the study is not perceived to be a serious deficiency. Finally, as regards the range of economic impacts considered, the present investigation explicitly deals with the impacts of the various alternative control techniques on aggregate income to forest landowners, levels of timber production, and governmental tax revenues or subsidy expenditures. While these items represent a fairly broad range of impacts, they do not completely exhaust the full array of factors which ideally should be considered. Among the relevant variables which have not been dealt with are: (1) off-site damages averted by reduced soil loss and consequent sedimentation, (2) governmental administrative or enforcement costs, (3) indirect or induced economic impacts attributable to an increase or decrease in landowner income or timber output, and (4) the equity implications of silvicultural nonpoint source controls. Failure to consider the full range of benefits and costs is unquestionably a significant limitation associated with the present investigation. Its practical importance is to complicate the task of drawing inferences about the economic rationality of imposing controls. In this study, time and data limitations were the primary reasons for restricting the range of economic variables considered. In future investigations of this type, if study areas are carefully chosen, it may be possible to estimate off-site damages using a procedure developed by Lee and Guntermann (1976). In addition, Everett and Miller have shown how the indirect or induced economic impacts associated with the imposition of silvicultural controls can be estimated if a regional "Input-Output" model is available for the study area (1975). These types of technical improvements should be introduced in the future. However, it is the opinion of the investigators that the methodology as developed and used in this study can still serve as a valuable aid to rational decision-making. The techniques that are described in this report entail additional limitations beyond those already identified. Prospective users need to be aware of these limitations, but it is felt that any discussion of them is best deferred until after the methodology itself has been presented. At this point the reader will be in a better position to evaluate their significance. The material in the remainder of this report has been organized around four chapters. The first describes the study area, giving special attention to the nature of the forest resource base. The second sets forth the methodology for economic impact assessment that was developed as part of this project. The third presents the results obtained by applying the chosen methodology to the selected study unit. Finally, the last chapter sets forth some concluding observations about the remaining methodological limitations previously referred to, future research needs, and the economic rationality of imposing silvicultural nonpoint source controls within the study area.
Optimal Operation of Large Agricultural Watersheds with Water Quality Restraints
(Texas Water Resources Institute, 1978-04) Hann, R. W.; Williams, J. R.
Improved technology is needed for use in properly managing large agricultural watersheds. Proper watershed management means selecting land uses that are appropriate for each subarea, using erosion control measures where necessary, and applying fertilizers at rates that maximize agricultural production without polluting the environment. Watershed runoff and industrial and municipal effluents pollute streams and reservoirs. Point source pollution (industries and municipalities) can be monitored. Nonpoint-source pollution (watersheds) is widely dispersed and not easily measured. Mathematical models are needed to predict nonpoint-source pollution as affected by watershed characteristics, land use, conservation practices, chemical fertilizers, and climatic variables. Routing models are needed to determine the quality of water as it flows from nonpoint sources through streams and valleys to rivers and large reservoirs. Models are also needed to determine optimal strategies for planning land use, conservation practices, and fertilizer application to maximize agricultural production subject to water quality constraints. Three of the most important agricultural pollutants are suspended sediment, phosphorus, and nitrogen. Robinson [1971] pointed out that sediment is the greatest pollutant of water in terms of volume. Sediment also transports other pollutants, like phosphorus and nitrogen. These two elements are principally involved in lake eutrophication. Frequently algae blooms develop in nutrient-laden water and cause it to have an off-taste and an unpleasant odor. The odor of decaying plants becomes offensive; fish are killed because of reduced dissolved oxygen in the water, and recreation is deterred. The objective of this research was to develop models for use in managing large agricultural watersheds to obtain maximum agricultural production and to maintain water quality standards. The models were designed to: 1. Simulate daily runoff, and sediment, phosphorus, and nitrogen yields from small watersheds (areas < 40 km2) and determine frequency relationships. 2. Route various frequency hydrography and sediment, phosphorus, and nitrogen yields from subwatersheds through streams and valleys of large agricultural watersheds (areas < 2500 km2) to obtain frequency relationships at the entrance of a river or reservoir. 3. Determine strategies that are acceptable to the decision makers (land owners and operators) for planning land use, fertilizer application, and conservation practices on subwatersheds. 4. Determine the optimal strategy for each subwatershed to maximize agricultural production for the entire watershed subject to water quality constraints. Generally, water-quality models are developed by adding chemical modeling components to existing runoff and sediment models because runoff and sediment provide transportation for chemicals. Several conceptual models for predicting chemical yields from small watersheds have been presented [Crawford and Donigian, 1973; Donigian and Crawford, 1976; Frere, et al., 1975; Hagin and Amberger, 1974; Kling, 1974; Johnson and Straub, 1971]. However, these models are not applicable to large watersheds because they have no routing mechanism. For this reason, runoff, sediment, and nutrient models were refined and developed here for application to large watersheds. Probably, the most widely used and accepted model for predicting runoff volume is the Soil Conservation Service (SCS) curve number system [U.S. Soil Conservation Service, 1972]. The SCS model was modified by adding a soil-moisture-index accounting procedure [Williams and Laseur, 1976]. The modified water yield model is considerably more accurate than the original SCS model. On a watershed near Riesel, Texas, the modified model explained 95% of the variation in monthly runoff as compared with 65% for the original model. The water-yield model was refined here by replacing the climatic index (lake evaporation) with daily consumptive water use for individual crops. Besides predicting individual storm runoff volumes, it is also necessary to predict hydrographs and to perform flood routing for water quality modeling on large agricultural watersheds. HYMO, a problemoriented computer language for building hydrologic models [Williams and Hann, 1973] was selected to compute hydrographs and perform flood routings. Worldwide use has shown that HYMO is convenient and reliable for extremely varied hydrologic conditions. The Variable Travel Time (VTT) flood routing method [Williams, 1975a] used in HYMO is about as accurate as an implicit solution of the unsteady flow equations of continuity and motion and is free of convergence problems. The USLE [Wischmeier and Smith, 1965] is the most widely used and accepted erosion model. It can be used to predict long-term average annual sediment yields for watersheds by applying a delivery ratio. However, the USLE was not designed for application to individual storms and is, therefore, not appropriate for individual storm water quality modeling. The USLE was modified [Williams, 1975c] by replacing the rainfall energy factor with a runoff factor. The modified universal soil loss equation (MUSLE) increased sediment-yield-prediction accuracy, eliminated the need for delivery ratios, and is applicable to individual storms. In tests with data from Riesel, Texas; Chickasha, Oklahoma; Oxford, Mississippi; Treynor, Iowa; Hastings, Nebraska; and Boise, Idaho, MUSLE generally explained 80% or more of the variation in individual storm sediment yield for each watershed. These tests included 60 watersheds with areas ranging from 0.01 to 234 km2 and slopes ranging from less than 1 to about 30%. The MUSLE was combined with the modified SCS water-yield model and HYMO to form a daily runoff-sediment prediction model [Williams and Berndt, 1976]. Satisfactory results were obtained when the runoff-sediment model was tested with data from 26 watersheds in Texas. The MUSLE is useful in predicting sediment yield from small watersheds (area < 40 km2), but sediment routing is needed to maintain prediction accuracy on large watersheds with nonuniformly distributed sediment sources. A sediment routing model was developed for large agricultural watersheds [Williams, 1975b] and has had limited testing. The sediment routing model was refined here and combined with nutrient-loading functions to develop a sediment-phosphorus-nitrogen routing model. Nitrogen and phosphorus loading functions [McElroy, et al., 1976] were developed for use on small agricultural watersheds. The loading functions were designed for predicting long-term average annual phosphorus and nitrogen yields based on predicted sediment yield, nutrient concentration in the soil, and enrichment ratios. However, there is no provision for predicting nitrate yield, since it is not attached to the sediment. There are no functions provided for determining nutrient concentrations in the soil as affected by fertilizer application. Also, relations were not developed for predicting enrichment ratios. Here the loading functions were adapted to individual storm prediction of phosphorus and nitrogen yields from small watersheds. A nitrate component was added and the enrichment ratios were related to particle-size distributions of the soil and the sediment. Since water quality models are not well developed for large agricultural watersheds, little has been done to develop models to determine optimal watershed management strategies subject to water quality constraints. Onishi and Swanson [1974] used linear programming to determine crop systems and practices that are economically optimal on a 4.86-km2 watershed subject to sediment and nitrogen constraints. Wade, et al. [1974] described a model that uses linear programming to minimize national agricultural production costs subject to meeting agricultural production demands and sediment yield constraints. Miller and Gill [1976] used a linear programming model to maximize net revenue to farm firms constrained by acreage limits and soil loss limits. Heady [1976] developed a national model to minimize the cost of producing and transporting farm commodities subject to soil loss and other constraints. None of these models are directly applicable to large agricultural watershed management, because only soil loss or nutrient losses are considered constraints. By including routing models, yields of sediment, phosphorus, and nitrogen can be determined and used as constraints. Considering yields to rivers or reservoirs provides more flexibility in management and higher potential agricultural production for the large watershed. Soil loss may not contribute to pollution because it may never reach a point to cause damage (permanent stream or reservoir). Yields of sediment, nitrogen, and phosphorus depend upon location of the source within a watershed, hydraulic efficiency of the channels, and the particle-size distribution as well as soil loss. If only soil loss is considered as a constraint, agricultural production cannot be truly maximized. The model presented here uses linear programming to maximize agricultural utility subject to constraints of sediment, phosphorus, and nitrogen yields at the watershed outlet. Decision analysis, as described by Raiffa [1970], is used to determine strategies that are acceptable to the decision makers (landowners and land operators) and to calculate the utility of the strategies. A strategy specifies land use, fertilization rate, and conservation practice. Utility is described with a multiattribute utility function based on gross income, production cost, dependability, and disease, insect, and weed control. Utility theory expresses the decision makers' preferences on a scale from zero to one. This provides for easier and clearer decisions because attributes with various units can be compared and combined directly. To apply decision analysis, each subwatershed is subdivided according to land capability classes. This simplifies the selection of strategies for the decision maker because different land classes have different production and pollution potentials. The number of possible strategies for operating each land capability class within a subwatershed approaches infinity, but the number can be reduced greatly by considering only strategies that are acceptable to the decision makers. Generally, crop production records are not adequate to evaluate the attributes for all strategies. However, the analyst or modeler can evaluate the attributes through the use of subjective probability distributions. Raiffa [1970] suggested special techniques for developing subjective probability distributions by interviewing the decision makers. Each year as the crops are harvested, the probability distributions are revised using Bayes' Theorem [1763] to include the observed data. Since there is usually more than one decision maker per subwatershed, most decisions concerning utility functions and probability distributions are group decisions. Raiffa [1970] suggested using Pareto-optimality in making group decisions. A joint action is Pareto-optimal if no alternative action exists that is at least as acceptable to all and definitely preferred by some. Decision analysis has been used very little in water-resources planning. McCuen [1973] used decision analysis to determine benefits from recreation facilities; Dean and Shih [1973] showed the advantages of subjective decision making for urban water resources development; and Russell [1974] applied decision theory to reservoir operation.
A Cross-Sectional Investigation of the Determinants of Urban Residential Water Demand in the United States, 1960 and 1970
(Texas Water Resources Institute, 1978-05) Beattie, B. R.; Foster, H.S.
This research was undertaken to specify and estimate a model relating household demand for urban water to its principal determinants. Four specific tasks were accomplished: 1. An appropriate economic demand model for urban-residential water supplies was postulated. An improved specification of the rainfall variable was developed to account for turf maintenance demand. The price of water was specified in exponential form making its elasticity price dependent. 2. Parameters of the model were estimated based on pooled data representing a cross-section of U.S. cities. 3. Parameters were estimated for a regionalized version of the model by incorporating sets of dummy variables. Tests for statistical differences among key economic coefficients were made to ascertain regional differences, if any. 4. Parameters were estimated for a model disaggregated by size-of-city categories again by incorporating dummy variable sets. Tests for statistical differences among key economic coefficients were made to ascertain differences among size-of-city categories, if any. The demand models were fitted using 1960 and 1970 data and ordinary least squares regression techniques. Explanatory variables included price, income, precipitation (during the defined growing season) and number of residents per meter in addition to sets of dummy variables on the constant factor and price and income coefficients. The results suggest that size of city is not statistically significant in determining the residential demand for urban water. However, regional differences are significant. For the regional model, price, income, and residents per meter were significant at the 1 percent level for the 1960 data; price and precipitation were significant at the 1 percent level for the 1970 data. R2-values were .74 and .71 for the 1960 and 1970 data, respectively. Income and price elasticities are presented for all regions at the mean price level and for one standard deviation above and below this price level. Mean price level elasticities ranged between -.30 and -.82 and between -.33 and -.67 for the 1960 and 1970 data, respectively, suggesting an inelastic residential water demand at present price levels. The elasticity estimates derived from the regional coefficients of this study compare favorably with those of earlier more micro-level analyses.
An Economic Analysis of Erosion and Sediment Damage in the Duck Creek Watershed, Dickens County, Texas
(Texas Water Resources Institute, 1978-08) Harris, B. L.; Reneau, D. R.; Taylor, C. R.
The Federal Water Pollution Control Act Amendments of 1972, Public Law 92-500, established a national goal of eliminating the discharge of pollutants into the nation's waterways by 1985. As a step toward that goal an interim water quality standard of "fishable, swimmable waters nationwide" by July 1, 1983 was determined. Under section 208 of this law, each state was required to establish a "continuing planning process" to define controls for agricultural non-point sources of water pollution. Section 208 calls for the development of state and area-wide water quality management plans The plans are to include "a process to (i) identify if appropriate? agriculturally and silviculturally related non-point sources of pollution, including runoff from manure disposal areas, and from land used for livestock and crop production, and (ii) set forth procedures and methods (including land use requirements) to control to the extent feasible such sources." The water quality issue of concern in this study is fertilizer and pesticide residuals carried into waterways by sediment. Since sediment is a potential transporter of pollutants, practices to control agricultural non-point source pollution would probably be aimed at reducing soil loss. Conservation and conservation related practices are, at present, considered the best technical practices to abate agricultural non-point source pollution. This study examines the economic impact of various policies that could be used to reduce soil loss. Both regulatory and voluntary policies are considered. Economic impacts examined include: (a) impacts of the policies on farm income; (b) government costs associated with the policies, including administration costs; (c) off-site sediment damages that would be abated; and (d) social desirability of the policies. The first section of the report describes the selected "Best Management Practices" and examines the on-farm economics of soil conservation. Then, the second section postulates various sediment damage control options and models the economic consequences, both to agricultural producers as a group? and to society of implementing them.
An Economic Analysis of Erosion and Sediment Damage in the Lower Running Draw Watershed
(Texas Water Resources Institute, 1978-08) Mueller, P. E.; Lacewell, R. D.; Harris, B. L.; Reneau, D. R.; Taylor, C. R.
The development and implementation of agricultural non-point source (NPS) pollution control plans was mandated by the 1972 Federal Pollution Control Act Amendments, Public Law 92-500. The purpose of this particular report is to present the results of a study on the economic impact of implementing potential agricultural NPS pollution controls in Lower Running Water Draw watershed. The study focuses on: (a) the effects of erosion control on farm income, (b) off-site sediment damages in the watershed; (c) the costs of administering and enforcing alternative erosion controls, and (d) on-farm economics of soil conservation practices. Erosion controls considered include the traditional voluntary programs combined with economic incentives as well as possible regulatory programs. The focus of the study is on erosion and sedimentation because sediment is a potential transporter of pollutants. Practices to control agricultural non-point source pollution would probably be aimed at reducing soil loss. Conservation and conservation related practices are, at present, considered the best technical practices to abate agricultural non-point source pollution. This is a study of both conservation and environmental economics, two areas that tend to be closely related. For this project, the concern was over potential pollution (an off-site problem), but because of long-run farm income consequences, this concern cannot be separated from conservation problems (an on-farm problem). Accordingly, the report contains substantial information on the short and long-run on-farm benefits and costs of various soil conservation practices for the specific soil mapping units in Lower Running Water Draw watershed. The results of this study are applicable to the majority of the soils in the High Plains Land Resource Area. Only sheet and rill erosion are considered in the study. The first section of the report describes the selected "Best Management Practices" and examines the on-farm economics of soil conservation. The second section postulates various sediment damage control options and models the economic consequences of implementation, both to agricultural producers as a group, and to society.
An Economic Analysis of Erosion and Sedimentation in Lavon Reservoir Watershed
(Texas Water Resources Institute, 1978-10) Harris, B. L.; Reneau, D. R.; Taylor, C. R.
Public Law 92-500 - the 1972 Federal Water Pollution Control Act Amendments - mandates the analysis of agricultural non-point source (NPS) pollution controls. This report presents the results of a study of the economic impact of implementing potential agricultural NPS pollution controls in the watershed above Lavon Reservoir. The study focuses on: (a) effects of erosion controls on farm income, (b) off-side sediment damages in the watersheds; (c) costs of administering and enforcing alternative erosion-sedimentation controls, and (d) effects of adopting cotton pest management methods. Erosion controls considered include possible regulatory programs as well as voluntary programs combined with economic incentives. While the stimulus for this study was concern over pollution (an off-site problem) it can not, because of long-run farm income consequences, be separated from conservation problems (an on-farm problem). Thus, the study is as much an analysis of conservation economics as it is an analysis of environmental economics. Accordingly, the report contains substantial information on the short and long-run on-farm benefits and costs of various soil conservation practices for all soil mapping units in Lavon watershed The results are applicable to much of the Blackland Prairies Land Resource area.
Erosion and Sediment Damages and Economic Impacts of Potential 208 Controls: A Summary of Five Watershed Studies in Texas
(Texas Water Resources Institute, 1979-01) Taylor, C. R.; Reneau, D. R.; Harris, B. L.
This report summarizes results of economic analyses of erosion and sedimentation in five agricultural watersheds in Texas (see fig. 1). Economic analyses of the study areas considered both the on-farm economics of soil conservation and the economic consequences of various sedimentation control options. These topics were joined in the studies because they deal with different facets of the same problem. Unlike some potential pollutants, soil particles transported from a farmer's field that may become a problem downstream are a valuable resource, not a waste product. Because soil is valuable in itself, some level of soil conservation is going to be economically desirable even if downstream damages are not present or are not considered by the farmer. Results of the studies show that soil conservation does indeed pay in many situations and that its value is greater the longer the planning horizon of a farmer. This suggests that an educational program in this regard may reduce sediment damage while increasing farm income at the same time . Sediment can cause environmental damage (off-site costs) both directly and indirectly. Directly, the soil particles can cause environmental damage by filling up reservoirs and flood control structures and by deposition in other places. Indirectly, sediment can cause environmental costs by carrying plant nutrients that are potential pollutants. For the study watersheds, no evidence was found that the concentration of plant nutrients in the water posed health hazards to livestock or humans, nor caused undue eutrophication in the watersheds. Consequently, the study focused on off-site sediment damages resulting from shortened economic lives of reservoir and flood control structures and from sediment deposition in the watershed. Annualized off-site sediment damages ranged from a high of 26 cents per ton of gross erosion in Lake Lavon watershed to 14 cents per ton of gross erosion in Duck Creek, to 13.5 cents per ton of gross erosion in Lower Running Water Draw, to a negligible amount in Turkey Creek and Cameron County. These estimates are considerably lower than off-site sediment damages in corn belt watersheds (Lee & Guntermann). Policy Options for Controlling Sediment Public policies that can be implemented to abate off-site sediment damages include direct regulation, provision of economic incentives, education, and public investment. For point sources of pollutants, regulations are typically directed toward the pollutant at or near the point of emission into waterways. However, this is infeasible with non-point sources such as sediment because they enter waterways at an infinite number of points. Hence, regulations must be directed toward the practices that cause erosion and thus sedimentation. The economic incentive option includes alternatives such as Federal or State cost-sharing for adoption of conservation practices, and disincentives such as taxes or penalties on erosion. Education is a viable policy option in situations where producers are not adopting soil conservation practices that would be profitable. In these situations a successful education program would increase producer's income as well as reducing off-site sediment damages. Public investment could be used to pay for dredging sediment from reservoirs and flood control structures to prevent loss of flood control, water supply and recreational benefits. Social benefits and costs of various policy options based on direct regulation, taxation, and provision of economic incentives were estimated for three watersheds: Lake Lavon, Duck Creek, and Lower Running Water Draw. Items considered in the benefit-cost analysis were: (a) farm income consequences; (b) off-site sediment damages abated; (c) governmental cost or revenue; and (d) administration and enforcement costs associated with each policy. The major conclusion of this social benefit and cost analysis is that off-site damages are not large enough to warrant controls on agricultural activities in any of the watersheds; that is, the costs to society of controls exceed the total benefits to society for all of the policy options considered. Another conclusion is that an education program that emphasizes the on-farm profitability of conservation practices may reduce sediment damages while simultaneously increasing farm income.
An Economic Feasibility Study of Irrigated Crop Production in the Pecos Valley of Texas
(Texas Water Resources Institute, 1979-03) Whitson, R. E.; Lindsey, K.; Hardin, D. C.; Lacewell, R. D.; Condra, G. D.
Public concern over the potential effects of energy price increases on the U.S. food and fiber system has been dramatically justified in the Trans Pecos region of Texas where a 450 percent increase in the price of natural gas was followed by the idling of thousands of irrigated acres and the departure of many of the farmers. This study was conducted to provide the answers to two questions: (l) Can an irrigated farm survive in the Trans Pecos? and (2) If it survives, how profitable will it be? Coyanosa, one of the irrigated areas of the Trans Pecos, was selected as a study area, and the St. Lawrence area of the Edwards Plateau was selected to provide comparative estimates of survival and profitability. A modified MOTAD linear programming-simulation model was developed to generate estimates of survival and profitability by recursive simulation of multiple time periods, as follows: (l) development of a farm plan, (2) generation of stochastic prices and yields, (3) simulation and evaluation of the farm plan in operation, and (4) update of the planning situation to reflect adjustments in expected prices, expected yields, and credit restrictions. The model then returns to step l for simulation of the next time period. The model was applied to the Coyanosa and St. Lawrence regions under alternative future scenarios for inflation rates, energy prices, crop prices, and interest rates. The Coyanosa model was also applied under most likely scenario conditions to analyze the effects of alternative levels of risk-aversion and alternative tenure situations. Each application included 20 simulations of a 1O year planning horizon to develop a distribution of outcome. The Coyanosa farm survived about 8 years under the optimistic scenario and 5 years under all other scenarios. The most likely rate of survival was 20-30 percent with a range of 1O percent to 65 percent for other scenarios. The average life and rate of survival was higher for the St. Lawrence farm under all scenarios. The internal rate of return on equity capital for the Coyanosa farm was 36.8 percent under the optimistic scenario and negative under all other scenarios. The rate of return for St. Lawrence was not significantly different for the optimistic scenario; however, it was higher than Coyanosa for all other scenarios. The level of risk-aversion described by the baseline model appears to be relatively high compared to other studies, but there are indications that it may be relatively low for the St. Lawrence area. Both rate of return and survival increased in response to decreased levels of risk-aversion, however, the latter result may be related to the specification of the risk restraint. Land purchase provided higher estimates of survival and profitability than rental or combined rental and purchase. These results seem to relate to the finding that traditional crop share rental arrangements are unsatisfactory for the Coyanosa area. It was concluded from this study that (l) survival and profitability of irrigated crop production in the Coyanosa area will depend greatly upon future levels of inflation, energy prices, crop prices, and interest rates, (2) survival and profitability for Coyanosa will most likely be lower than St. Lawrence, and (3) land purchase provides greater potential survival and profitability than traditional crop share rental arrangements. These conclusions were limited by need for additional research regarding the effects of beginning equity levels and consideration of risk in farm planning. Conclusions were also limited by the data and assumptions utilized in the study.
The Economic Value of Irrigation Water in the Western United States: An Application to Ridge Regression
(Texas Water Resources Institute, 1979-03) Beattie, B. R.; Frank, M. D.
Reliable estimates of the demand characteristics of irrigation water are crucial to successful water policy formulation in the West. Although various studies concerning irrigation water demand exist in the literature, most are somewhat limited in scope and present their results in varied forms. Thus, comparison of results presents a problem. This study follows a more comprehensive approach by determining the demand characteristics, viz., water value, demand elasticities, etc., for major western irrigated regions. These results should prove useful in water policy formulation and evaluation. Eleven homogeneous regions were identified as major irrigated areas of the West. Agricultural output (in value terms) in each region was hypothesized to take the form of a multiplicative function with nine domain variables, i.e., irrigation water applied, value of land and buildings, hired labor expenditures, fuel and lubricant expenditures, fertilizer and lime expenditures, feed expenditures, value of machinery inventory, value of livestock inventory and miscellaneous expenditures. Using 1969 Census of Agriculture data, each regional function was statistically fit using both ordinary least squares (OLS) and ridge regression. As expected, parameter estimates under OLS were highly unstable due to high correlations among the explanatory variables (multicollinearity). One-third of the estimated coefficients took on nonsensical signs and the standard errors were generally high. To circumvent the multicollinearity problem ridge regression was employed. While admittedly a biased estimation technique, the credibility of the estimates appeared to increase. All parameter estimates, except for one out of 99, took on the expected positive sign and the standard errors were decreased in every case. Returns to scale were estimated to vary from a high of 1.200 in the Northwestern Ogallala to a low of .887 in the Lower Rio Grande Basin. Overall, the functions estimated with ridge regression were more compatible with theoretical expectations than those based on OLS estimates. From the fitted production functions, the demand for irrigation water was derived for the long run, two intermediate runs and the short run. Generally, water demand was found to be slightly elastic for all lengths of run considered with the more elastic demand in the Desert Southwest and Upper Colorado Basin, and slightly less elastic demand in the Snake-Columbia, Lower Rio Grande Basin and Northwestern Ogallala. The quantity of water applied was found to be most sensitive to product price in the Central California, Desert Southwest, Upper Colorado Basin and Northwestern Ogallala Regions. In terms of cross-factor effects, water application rates were found to be most responsive to changes in the prices of land and labor for all regions. Marginal irrigation water values for each length of run considered were estimated for 1969 at the respective regional mean values of water usage, fixed input levels and variable input prices. These estimated values varied from a high of $27.79 for the long run in Central California to a low of $1.71 in the short run for the Snake-Columbia Basin. It appears that the value estimates may be distorted in some instances due to the influence of livestock variables in the model. Subsequent research should attempt to correct this deficiency. Projections of values for 1974 (a census year) and 1978 were made with the assumption of no change in technology and level of "fixed" input and water - usage since 1969. Though a somewhat gross projection, water values were found to increase until 1974 and then decrease in 1978. These projections should serve as a basis for possible later validation by other researchers.
An Economic Analysis of Agricultural Soil Loss in Mitchell County, Texas
(Texas Water Resources Institute, 1979-03) Taylor, C. R.; Reneau, D. R.; Harris, B. L.
The Federal Water Pollution Control Act Amendments of 1972, Public Law 92-500, established a national goal of eliminating the discharge of pollutants into the nation's waterways by 1985. As a step toward that goal an interim water quality standard of "fishable, swimmable waters nationwide" by July 1, 1983 was set. Under section 208 of this law, each state was required to establish a "continuing planning process" to define controls for agricultural nonpoint sources of water pollution. Section 208 calls for the development of state and area-wide water quality management plans. The plans are to include "a process to (i) identify if appropriate, agriculturally and silviculturally related non-point sources of pollution, including runoff from manure disposal areas, and from land used for livestock and crop production, and (ii) set forth procedures and methods (including land use requirements) to control to the extent feasible such sources." In an earlier group of technical reports (TR 87, 88, 90, 93) in this series a model was developed to measure the net social benefits from controlling agricultural sediment given various policy options. This was done by contrasting benefits to be gained from reducing the sediment load in a watershed against costs involved in achieving that reduction using various voluntary or mandatory policies to accomplish the reduction. It was a major conclusion of these studies that no policy that restricted soil loss to less than that which was economically desirable from the farmers own viewpoint would generate benefits greater than the costs involved. This finding, in the watersheds of major sediment control concern lead to a decision to change the base area for this report to a county instead of a watershed and to only deal with the on-farm consequences of various management practices. These on-farm consequences would include the changes in topsoil loss and the yield losses that result from losing topsoil. Also included are profit levels that could be expected from different management practices and how the present value of a stream of these profits would vary over different planning horizons.
Economically Optimum Irrigation Patternsfor Grain Sorghum Production: Texas High Plains
(Texas Water Resources Institute, 1979-03) Zavaleta, L. R.; Lacewell, R. D.; Taylor, C. R.
Agricultural production and associated economic effects of irrigation on the Texas High Plains are seriously threatened by a rapidly declining groundwater supply and a swift upward trend in energy costs. To optimize the amount of irrigation water to be applied during specified periods of the production process, a stochastic open-loop feedback control policy was built into a grain sorghum growth simulation model. The control policy operated under the basis of constant revision of the expectations generated at every starting point for each of the production periods. If discrepancies between the expected and the realized values existed, then, based on current conditions a reevaluation of the control variable, irrigation water, was made and the decision for the first period adopted. This process continued throughout each period of the growing season. Within the stochastic policy designed, the values for the control variable were obtained by numerical search. The model was applied to estimate optimal irrigation strategies and the impact of fuel curtailments on them. Initially, optimal irrigation strategies were developed under the assumption of perfect knowledge. Under this assumption, the results indicated there was not a unique strategy to be applied at all times. The quantities of irrigation water to apply at each period depended on the initial or starting conditions. Since one of the purposes of building the model was to make it perform under stochastic or real world conditions, the assumption of complete knowledge was relaxed to consider the case where the climatic environment was unknown. As in the deterministic case, the optimal amounts of irrigation water, by period. It was also observed, that with the open-loop feedback control, the results obtained for yields did not differ substantially from those obtained in the perfect knowledge case. The discrepancies among the two cases were primarily in the optimal amount of water applied and therefore in net returns. In the stochastic case, the use of irrigation water had a mean value approximately 25 percent more than in the case of perfect knowledge. The effect of a fuel or irrigation curtailment was estimated for alternative time spans. When curtailments had a length of 10 days, there were no perceptible changes in the amount of net returns or yields, as compared to the no-curtailment case. The implication drawn was that by having frequent irrigation periods and applying optimal amounts of water, the adverse effects of 10-day curtailment periods were buffered. The cases of twenty and thirty-day periods were found to have highly negative effects on the outcomes, especially net revenues, which decreased about 50 percent (from $99 to $50) in the curtailment case of 40 - 70 days after plant emergence compared to the no-curtailment value. The effects were not only on a decreased amount of returns perceived but also on an increased spectrum of relative fluctuation (from 18 percent to 68 percent for the same situations mentioned above). It was also found that for the same time-span type of curtailments the effects were conditioned to the period in which they Occurred. However, the 20 or 30 day curtailment period might be applicable to much shorter actual fuel curtailment periods. Producers lose not only the time of fuel curtailments, but also, they must cover many acres with a limited number of wells. As a result, a 10-day fuel curtailment could easily result in a 20 to 30 day delayed irrigation. To summarize, improved irrigation distribution technology could result in increased yields and less irrigation water by simply having very close control on timing and quantity of water applied.

Browse

Browsing Texas A&M University by Issue Date