Journal of Irrigation and Drainage Engineering

This study uses five years of field data from the Land Retirement Demonstration Project located in western Fresno County of California to develop a comprehensive theoretical and numerical modeling framework to evaluate the specific site conditions required for a sustainable land retirement outcome based on natural drainage. Using field data, principles of mass balance in a control volume, the HYDRUS-1D software package for simulating one-dimensional movement of water, heat, and multiple solutes in variably-saturated media, and a model-independent parameter optimizer, the processes of soil water and solute movement in root zone and deep vadose zone were investigated. The optimization of unsaturated soil hydraulic parameters and downward flux (natural drainage) from the control volume against observed vadose zone salinity levels and shallow groundwater levels yield difficult to obtain natural drainage rate as a function of water table height within the control volume. The results show that the unsaturated soil hydraulic properties and the downward flux from the soil profile are the critical parameters. A “natural drainage approach” to sustainable land management for drainage-impaired land is proposed. With this approach it is feasible to design a sustainable land use regimen for drainage-impaired lands in general and retired lands in particular.

In the 1990s, Turkey started a fast transfer program in which a large proportion of government-managed irrigation systems were put into the hands of Water Users’ Associations (WUAs) in a very short space of time. One of the first systems to be handed over was the Gediz Basin. This study aims to set out the effects of the transfer of irrigation management in this basin on water and land productivity and water supply. For this purpose, the indicators of productivity and water supply proposed by the International Water Management Institute have been used to show changes between the pretransfer, transfer, and post-transfer periods. WUA averages for the post-transfer period calculated from the results ranged $\mathrm{\$}2,076–\mathrm{\$}2,898{\text{ha}}^{-1}$ for output per command area, $\mathrm{\$}2,747–\mathrm{\$}4,585{\text{ha}}^{-1}$ for output per irrigated area, $\mathrm{\$}0.26–\mathrm{\$}0.68{\text{m}}^{-3}$ for output per irrigation supply, $\mathrm{\$}0.30–\mathrm{\$}0.63{\text{m}}^{-3}$ for output per unit water consumed, 0.88–1.49 for relative water supply, and 0.99–1.99 for relative irrigation supply. During the period evaluated by the study, there was a decline in water supply indicators, as against a steady increase in the productivity of water and land use. The basic reason for this decrease in supply is the long-lasting and ongoing drought in the region.

Dependency of water demands on the climate variation occurs especially in regions where agricultural demand has a significant share of the total water demands. The variability between demands that are based on annual climate conditions may be larger than the uncertainty associated with other explanatory variables in long-term operation of an irrigation dam. This paper illustrates certain benefits of using variable demands for long-term reservoir operation to help manage water resources system in Zayandeh-rud river basin in Iran. A regional optimal allocation of water among different crops and irrigation units is developed. The optimal allocation model is coupled with a reservoir operating model, which is developed based on the certain hedgings that deals with the available water and the water demands mutually. This coupled model is able to activate restrictions on allocating water to agricultural demands considering variation of inflow to the reservoir, variation of demands, and the economic value of allocating water among different crops and irrigation units. Using this model, long-term operation of Zayandeh-rud dam is evaluated considering different scenarios of inflow to the reservoir as well as agricultural demands. The results indicate that the use of operating rules which consider variable demands could significantly improve the efficiency of a water resources system in long-term operation, as it improves the benefit of Zayandeh-rud reservoir operation in comparison with conventional water supply approaches.

This study used artificial neural networks (ANNs) computing technique for infilling missing daily saltcedar evapotranspiration (ET) as measured by the eddy-covariance method. The study site was at Bosque del Apache National Wildlife Refuge in the Middle Rio Grande Valley, New Mexico. Data was collected from 2001 to 2003. Several ANN models were evaluated for infilling of different combinations of missing data percentages and different gap sizes. The ANN model using daily maximum and minimum temperature, daily solar radiation, day of the year, and the calendar year as inputs showed the best estimation performance. Results showed coefficient of determination $\left(R^2\right)$ of 0.96, root-mean-square error (RMSE) of 0.4 mm/day for 10% missing data and a maximum of half-month gap size data set. Missing data greater than 30% and maximum data gap size greater than 3 months resulted in $R^2$ less than 0.90 and RMSE greater than 0.6 mm/day. The results from this study suggest that infilling of daily saltcedar ET using ANN and readily available weather data where the ET observations exist before and after the gap is a reliable and convenient method. It could be used to obtain continuous ET data for modeling and water management practices.

A preliminary investigation into the feasibility of erecting a solar chimney power plant requires a model incorporating all possible aspects of such a power plant and giving results on an hourly basis. Possible agricultural activities underneath the outer section of the solar collector would require a model predicting the changing state of the air due to evapotranspiration effects as it flows from the perimeter of the collector to the chimney in the center. The vegetation temperature and irrigation requirements need to be determined in order to ascertain how far inward crops may be planted without being subjected to heat stress. A small experimental glass roofed tunnel was constructed, planted with grass, and the changing state of the air, drawn over the grass by a fan, was determined using wet- and dry-bulb temperature measurements and the mass flow rate of the air. Starting off with a known air state inlet condition, conservation and the Penman-Monteith equations were applied to subsequent 1-m lengths of the tunnel and the state of the air at the outlet was predicted and compared with the measured state of the air. The predicted and measured values were found to be in agreement within experimental limits giving confidence in incorporating this model into the larger model of the solar chimney.

The use of low-impact development (LID) storm-water management facilities will grow with gains in understanding of their performance based on field tests. An innovative flow measurement system was designed and tested for monitoring of an interconnected system of underdrained LID components forming a site management strategy. Pressure transducers housed in stilling wells provided in-line flow measurements in pipes connecting the LID components. A combination of laboratory experiments, field measurements, and computer simulations was used to calibrate the flow measurement system to translate depth measurements to estimates of flow. The monitoring system is well suited for high-resolution temporal monitoring and provides important information for evaluating LID component performance. The measurement system is limited to open-channel flow, but calculations indicate that surcharge conditions are expected to occur at the case study site only under conditions more extreme than the 100-year storm event.

In this study the discharge coefficient for circular orifices of different size in two different sizes of riser pipe is investigated experimentally. This type of outlet structure is common in detention ponds to achieve runoff volume control from developed areas in order to meet outflow discharge and water quality requirements. The discharge coefficient is determined by recording the drop in pond water level with time as water flows out of the orifice. The discharge coefficient is found to be a function of head over the orifice, location of the orifice above the floor of the tank, and the ratio of the orifice diameter to riser pipe diameter. The discharge coefficient increases as the head over the orifice decreases and height of the orifice above the floor of the tank decreases. The discharge coefficient reduces as the ratio of the orifice diameter to pipe diameter increases and eventually reaches an asymptotic value. Also, with all other variables being the same, the discharge coefficient is lower for larger size riser pipe. An equation that is a function of head over the orifice and height of the orifice above the floor of the tank is fitted for each ratio of orifice diameter to piper diameter. The coefficients of the equation are found to be a function of the ratio of orifice diameter to piper diameter. A minimum coefficient of determination of 0.78 for the fitted equation suggests that the fit can be used to determine the discharge coefficient for orifices in circular riser pipes.

The question of watershed response to changes in land use and land cover has received a great deal of attention in the hydrologic literature. One of the primary tools for quantifying such changes has been the paired watershed approach. In general this approach applies a linear regression analysis to relate water yield from a control watershed to a physiographically similar watershed in close proximity, and to predict changes in yield following treatment. Although much research on paired watershed experiments has focused on quantification of the impacts of land-use and land cover changes on water yield, little attention has been brought to evaluating explicitly the methodology used to quantify such effects. An alternative method is proposed for examining treatment impacts and their duration, through the application of a cumulative recursive residual test of model stability. The results from a paired watershed study of ponderosa pine watersheds in north-central Arizona are analyzed using both a traditional linear regression analysis and a recursive residuals approach. The results suggest that the linear regression approach may fail to account for the true complexity of watershed response to vegetation treatments, by underestimating the interactions of treatment impacts, shifts in climatic drivers, and revegetation rates.