An overview is given for the general characteristics of the Republic of Yemen (ROY) related to water resources management and developments. The hydrological data needed for development processes of water supply projects in ROY are scarce or do not exist especially for small scale projects. For this case of inadequate data, some theoretical and empirical models used in evaluating resources potentials from small watersheds are presented through the different chapters and applied in Wadi Surdud catchment area as a case study. The applied models include SCS curve number method and the Modified Universal Soil Loss Equation (MUSLE). Direct runoff estimations were computed using the curve number method with daily rainfall data for 1988- 1992. For this estimate, the catchment area was divided into three basins, and the average rainfall was obtained using Thiessen polygon method. The annual water yields for each basin were obtained from the estimated direct runoff. These annual water yield volumes are then used in constructing the needed flow duration curves and in obtaining a runoff general equation with curves for extraction the equation's coefficient of each basin for different conditions ofCNs. Due to the deficiency of the required data for applying the MUSLE, it was applied only for basin# 2 in Wadi Surdud. The purpose of this application was to demonstrate the procedures for determining the different variables of the equation and for developing general curves for use in estimating the sediment yield directly from the relationship between the peak flows and the cropping factor. The developed models of predicting both of water yields and sediment yields can be improved to produce more reliable results by obtaining more accurate data for Wadi Surdud.

The feasibility study estimated that the Wonogiri Reservoir will be able to supply water with a 90 percent reliability. This estimation was supplied by frequency analysis. Twenty years of monthly streamflow data of the Solo River were used in these calculations. The current study estimates a 5.82 percent probability of failures, which is provided by water balance calculations. The streamflow data are extended by the first-order autoregressive (Markov) model. The generated streamflows are multiplied by a runoff factor. The feasibility study specified that a flood having 4,000 cms peak with the March-1966 flood standard hydrograph can be effectively reduced to 400 cms by the reservoir, where the water level will reach an elevation of 137.7 meters. The current study researches the reservoir's flood control ability by reservoir routing. Assuming the water level reaching 138.2 meters the reservoir can reduce a flood of 4,400 cms peak.

An analysis of NOAA'S Advanced Very High Resolution Radiometer (AV HRR) Normalized Difference Vegetation Index (NOVI) was made with gauged rainfall data and potential evapotranspiration estimates ( derived from the Penman equation) for the Republic of Niger's 1985 through 1992 rainy season. The purpose of this study is to (1) analyze the spatial and temporal variations in ground-derived NOVI in the Republic of Niger during the 1992 rainy season, (2) examine the variability and strength of the long-term and interannual relationship between satellite derived NOVI, grouped rainfall and potential evapotranspiration estimates and (3) compare the 1992 ground-based measurements of NOVI with long-term and short term satellite-derived NOVI. The West Central site of the National Atmospheric and Space Administration's (NASA) Hydrologic Atmospheric Pilot Experiment (HAPEX), located in the Republic of Niger, West Africa, 13° 32'N and 02° 31 'E was chosen to evaluate the accuracy and applicability of satellite data for use in areas where ground-based measurements are not possible. A transect of three climatological stations in Southern Niger was constructed. A general trend of decreasing rainfall and increasing potential evapotranspiration estimates with increasing latitude was observed. This transect demonstrated how variable rainfall is over a small region in Niger. The Republic of Niger's rainy season as a whole was examined over five different vegetation zones. The rainy season for Zones I and II (located furthest sou~) began in April, in May for Zone ill, and in August for Zone IV (located furthest north). Zone V which is located east of Zones II and ill, showed the rainy season starting in May. To demonstrate how vegetation responded to this spatial climate variation, I looked at the view taken by satellite NOVI. Zone I showed a sine curve distribution of greenness where maximum greenness occurred during the month of September, representing a one month lag after the peak rainy season in August. Zone I had the greatest NOVI values with Zone II showing lower NOVI values bQt with a similar sine curve distribution. Zone ill and IV showed little to no satellite • J NOVI response with the rainy season. Zone V showed a great increase in the satellite NOVI at the peak of the rainy season. NOVI data gathered at the ground of the HAPEX SAHEL West Central site taken at three homogeneous field sites (Fallow, Degraded and Grassland), were compared to NOAA' S satellite NOVI. Overall, satellite NOVI recorded lower values in comparison to the ground-based NOVI. This was due to the influence of moisture and water vapor in the atmosphere during the onset of the rainy season. Differences of scale in the two types of observations also played a role.

A water resources assessment of the Casa Grande Ruins National Monument (CAGR) was conducted using historical and recent data. The data were sorted and analyzed to determine whether the monument grounds have the potential for subsidence, and in particular, differential subsidence. Further research was conducted to ascertain the cause of the loss of the mesquite woodland on the monument grounds in the 1940's. To determine the potential for subsidence at the monument, a subsidence model was constructed based on geology developed from well logs of local wells. The model allowed the water table to fall from the predevelopment level to the present, and to possible future levels. The region of the Casa Grande Ruins National Monument has the potential for subsidence and differential subsidence on a geological basis, should the water table drop sufficiently. The majority of the mesquites on the monument grounds died in the 1940's. This has been attributed to groundwater pumping that lowered the groundwater table, but may also have been caused by drought, loss of a perched aquifer, disruption of overland flow by construction around monument grounds, and construction of the contour dykes at CAGR.

General water rights adjudications are now taking place in Arizona. The Gila River and Little Colorado River adjudications are among the largest court proceedings ever undertaken in the United States, involving more than 78,000 water rights claims scattered over 50,000,000 acres of land. The cost of individually proving such a number of individual claims in a formal trial setting would be enormous — often greater than the water's economic worth. Also, the time required to complete such a proceeding would take decades. Consequently, alternative procedures are needed to streamline the investigations and forestall a potentially serious water resource management problem. There are an estimated 22,800 stockwatering ponds (stockponds or stocktanks) in the Gila River Basin alone, and each potentially could be tried as an individual case. If small claims such as those for stockwatering could be considered de minimis in their impact on other higher priority uses, they might be adjudicated as one class of use, thereby fore-stalling a case-by-case trial of each individual water right claim. However, a major obstacle in granting special treatment to small claims lies in demonstrating to litigants that certain small water uses do not, in fact, have a discernible impact on other downstream water right holders. This study was undertaken to quantify the actual losses to a river system from stockwatering ponds, and to compare those losses to other naturally occurring impacts on the hydrologic system. Employing a watershed model, portions of the Walnut Gulch Experimental Watershed at Tombstone, Arizona, an area located within the San Pedro watershed, were analyzed. Storm runoff was simulated with and without the presence of stockponds. Different storm events and storage conditions were modeled in order to measure the impact of stockpond storage under a wide range of field circumstances. This study demonstrated that the hydrologic effects of stockwatering ponds are de minimis with respect to their impact on other water users many tens or hundreds of miles downstream on the river system. Stockpond numbers, capacities, volume/surface area relationships, quantification methods, and effective retention are also evaluated. Statutes in other states are reviewed for their approach to handling stockwatering uses.

The lagged responses of tree-ring indices to annual climatic or hydrologic series are examined in this study. The objectives are to develop methods to analyze the lagged responses of individual tree-ring indices, and to improve upon conventional methods of adjusting for the lag in response in regression models to reconstruct annual climatic or hydrologic series. The proposed methods are described and applied to test data from Oregon and Southern California. Transfer-function modeling is used to estimate the dependence of the current ring on past years' climate and to select negative lags for reconstruction models. A linear system is assumed; the input is an annual climatic variable, and the output is a tree-ring index. The estimated impulse response function weights the importance of past and current years' climate on the current year's ring. The identified transfer function model indicates how many past years' rings are necessary to account for the effects of past years' climate. Autoregressive-moving-average (ARMA) modeling is used to screen out climatically insensitive tree-ring indices, and to estimate the lag in response to climate unmasked from the effects of autocorrelation in the tree-ring and climatic series. The climatic and tree-ring series are each prewhitened by ARMA models, and crosscorrelation between the ARMA residuals are estimated. The absence of significant crosscorrelations Implies low sensitivity. Significant crosscorrelations at lags other than zero indicate lag in response. This analysis can also aid in selecting positive lags for reconstruction models. An alternative reconstruction method that makes use of the ARMA residuals is also proposed. The basic concept is that random (uncorrelated in time) shocks of climate induce annual random shocks of tree growth, with autocorrelation in the tree-ring index resulting from inertia in the system. The steps in the method are (1) fit ARMA models to the tree-ring index and the climatic variable, (2) regress the ARMA residuals of the climatic variable on the ARMA residuals of the treering index, (3) substitute the long-term prewhitened tree-ring index into the regression equation to reconstruct the prewhitened climatic variable, and (4) build autocorrelation back into the reconstruction with the ARMA model originally fit to the climatic variable. The trial applications on test data from Oregon and Southern California showed that the lagged response of tree rings to climate varies greatly from site to site. Sensitive tree-ring series commonly depend significantly only on one past year's climate (regional rainfall index). Other series depend on three or more past years' climate. Comparison of reconstructions by conventional lagging of predictors with reconstructions by the random-shock method indicate that while the lagged models may reconstruct the amplitude of severe, long-lasting droughts better than the random-shock model, the random-shock model generally has a flatter frequency response. The random-shock model may therefore be more appropriate where the persistence structure is of prime interest. For the most sensitive series with small lag in response, the choice of reconstruction method makes little difference in properties of the reconstruction. The greatest divergence is for series whose impulse response weights from the transfer function analysis do not die off rapidly with time.

Many planning decisions related to the land phase of the hydrologic cycle involve uncertainty due to stochasticity of rainfall inputs and uncertainty in state and knowledge of hydrologic processes. Consideration of this uncertainty in planning requires quantification in the form of probability distributions. Needed probability distributions, for many cases, must be obtained by transforming distributions of rainfall input and hydrologic state through deterministic models of hydrologic processes. Probability generating functions are used to derive a recursive technique that provides the necessary probability transformation for situations where the hydrologic output of interest is the cumulative effect of a random number of stochastic inputs. The derived recursive technique is observed to be quite accurate from a comparison of probability distributions obtained independently by the recursive technique and an exact analytic method for a simple problem that can be solved with the analytic method. The assumption of Poisson occurrence of rainfall events, which is inherent in derivation of the recursive technique, is examined and found reasonable for practical application. Application of the derived technique is demonstrated on two important hydrology-related problems. It is first demonstrated for computing probability distributions of annual direct runoff from a watershed using the USDA Soil Conservation Service (SCS) direct runoff model and stochastic models for rainfall event depth and watershed state. The technique is also demonstrated for obtaining probability distributions of annual sediment yield. For this demonstration, the deterministic transform model consists of a parametric event-based sediment yield model and the SCS models for direct runoff volume and peak flow rate. The stochastic rainfall model consists of a marginal Weibull distribution for rainfall event duration and a conditional log-normal distribution for rainfall event depth given duration. The stochastic state model is the same as employed for the direct runoff application. Probability distributions obtained with the recursive technique for both the direct runoff and sediment yield demonstration examples appear to be reasonable when compared to available data. It is therefore concluded that the recursive technique, derived from probability generating functions, is a feasible transform method that can be useful for coupling stochastic models of rainfall input and state to deterministic models of hydrologic processes to obtain probability distributions of outputs where these outputs are cumulative effects of random numbers of stochastic inputs.

Few studies have been made regarding the efficiency of water use in irrigation systems in operation. Therefore, in this work the search for methodologies to evaluate the actual efficiency of water use in a Mexican irrigation district as well as methods which may improve this efficiency is emphasized. The work has been divided into four parts. In the first part, the analysis of the economic activities in the irrigation district by means of linear programming has permitted finding the marginal productivity of water which is used as a shadow price for economic evaluation of the operating rules. In this part a relationship between the marginal productivity of water and the conveyance efficiency has also been found. In the second part, using hydrological historical data and a pattern of monthly water demand for crops obtained in the first part, control curves of the reservoir levels which permit knowledge of the probability of risk of spill and shortage were computed. Utilizing these curves and a simple linear programming model for finding the optimal economic annual average release, operating rules for the reservoir have been deduced. These rules were tested by means of a simulation model and their economic effectiveness was estimated using a benefit-cost analysis, showing a significant improvement in benefits for the farmers as a consequence of using these rules. In the third part, the conveyance losses in the canal network are analyzed using a linear regression between releases and deliveries. The proposed model permits an estimation of the conveyance efficiency and its division into two component factors, the intrinsic efficiency directly related to the physical characteristics of the canals, and the operational efficiency related to water management in the canal network. Knowing these components, it is possible to classify the conveyance losses as well as deduce operating rules for improving the operational efficiency. In making decisions about the methods to be used for improving the conveyance efficiency, benefits and costs must be taken into account. Therefore, a practical relationship for evaluating the economic feasibility of lining canals, considering those benefits and costs, is found as well as a method for economic evaluation of the operating rules. Finally, in the last part of this work, a practical methodology for estimating the application efficiency at the farm level in an irrigation district and small divisions as well is shown. This method is useful in finding where the problems in water use are more important within the district and which could be their principal causes. Utilizing data from experiments, which are available in most of the Mexican irrigation districts, production functions relating yields of crops to the amount of water applied and the percentage of moisture depletion in the soil before and during the flowering season of the crop, have been found. These functions can be used not only for obtaining the optimal economic depth of water to be applied and irrigation timing but also for deriving the optimal water use efficiency, whi6h, when related to actual values of this water efficiency in each subdivision of the district, permits the deduction of a practical water use efficiency index which is useful for detecting where the problems in water use are and what are the potential returns for the farmers in each of the considered subdivisions.

The compilation, collection, analysis, and simulation of UPRP streamflow and water-quality information were undertaken in order to assess the expected levels and variability of the quantity and quality of the surface waters in relation to the meteorology and hydrology of the area--the intended objectives of the project--and the modes of system operation. Under the two major phases of the study, important aspects which were examined were the availability and adequacy of the data base, and the applicability of modeling schemes to simulate the observed properties of the data. The major objective in the operational hydrology phase was to test the applicability of operational hydrology in a tropical environment. A stochastic model was fitted to the streamflow data of the extended UPRP inflows in order to serve as a generator of synthetic monthly streamflows which are used as inputs to operational studies of the project. As an initial requirement, the historical record was augmented by means of regional estimation techniques and a statistical data augmentation scheme. The percent deviation method of data augmentation was selected and applied, based on the results of a comparison of four augmentation methods. Two normalizing transformations were applied on the augmented-historical data in order to express them as statistical variables amenable to synthesis. These were the logarithmic transformation and Harter's table interpolation scheme. A time series analysis applied on the normalized data prescribed the adoption of the separate-monthly Matalas model for synthesis. The application of the model yielded synthetic streamflows which satisfactorily reproduced the correlation coefficients, means, and standard deviations of the augmentedhistorical monthly flows. Model extensions and refinements were recommended in order to surmount model limitations. In general, the applicability of operational hydrology in a tropical environment has been demonstrated. The quality of the UPRP surface water was characterized in order to provide background information which is essential in determining the suitability of the water for fishery development in the reservoir, for irrigation, and for domestic and industrial use. The Pantabangan reservoir was characterized in terms of observed patterns of temperature, dissolved oxygen, and salinity. An annual cycle was observed which exhibits intermittently disturbed and moderate stratification in the wet season, full circulation and isothermal condition during the cool, windy, and dry months, and a short warm period favorable to stratification prior to the heavy rains. Atmospheric reaeration was identified to be the major contributor of dissolved oxygen to the reservoir water. The application of the Markofsky-Harleman predictive model for reservoir temperature and dissolved oxygen emphasized the need for substantial data on the hydrology, meteorology, hydrodynamics, and water quality in the reservoir which are required as model inputs. The best agreement between observed and predicted temperature and DO was obtained for cool, windy, and dry months of December to February. Limitations in the input data and in the assumed parameters were observed. The available and collected water-quality data in the reservoir and streams of the UPRP indicated a salinity level as low as or less than 100 ppm in the headwaters to as high as 300 ppm in the outflows from the irrigation service area. The surface water is essentially the alkaline-bicarbonate type. The heavy runoff during the wet season produces a dilution of the TDS, but causes the conveyance of considerable amounts of sediment to the reservoir and river channels. An approximate salt balance for the project area yielded estimates of net amounts of salts leached from the area per season.

A gas-diffusion tracer experiment was conducted at the ChemNuclear, Inc., nuclear waste burial site near Barnwell, South Carolina, on June 1-10; 1981, testing a new methodology to measure the in situ gaseous diffusion characteristics of unsaturated porous media for the purpose of estimating the diffusive flux of volatile contaminants from the burial ground. The tracers used were CClBrF₂ and SF₆. They were released in the subsurface from permeation devices that closely approximate an ideal point-diffusion source. The permeation devices contain the tracer in liquid form and allow the tracer to escape at a constant rate by diffusion through a Teflon membrane. The release rates for CClBrF₂ and SF6 during the test were 105 and 3.3 nanograms/second, respectively. These compounds were selected on the basis of their compatabi1ity with the permeation-release device, their absence in the subsurface, and detectability in the part-per-tri11ion range in soil gas. Analyses were made in the field on a Varian 3700 series gas chromatograph equipped with an electron-capture detector. The instrument was modified to introduce soil gas through sampling valves and a Nafion tube desiccant. The diffusion sources were placed in the unsaturated soil at depths of 2 meters and 13 meters below land surface. Diffusive movements of tracer were monitored for a period of 7 days and tracer breakthrough was observed at points up to 3.5 meters away. Diffusion was modeled using a three-dimensional, continuous point source, transient-state, analytical model which allowed estimation of the effective diffusion coefficient of the porous media, and an independent assessment of the media's sorptive effects on the tracer gas. The model was calibrated using least squares and curve matching techniques, the latter of which enables a field technician to quickly interpret observed field data. Field values obtained for effective diffusion coefficient ranged from 0.026 to 0.037 cm²/sec. The average tortuosity factor observed for test site was 0.705.