Journal of Irrigation and Drainage Engineering

The subsurface drainage operation of shallow soils is characterized by sudden and brief peak flows followed by long‐lasting tail recessions. A field experiment was conducted on a seasonally waterlogged, shallow loamy soil in Arrou, France, under temperate climate. Rainfall and drainage discharge were recorded on an hourly basis, as well as water tension profiles and water‐table levels at different distances from the trench. Observed peak flows are related to sudden increases in the horizontal hydraulic gradients near the trench and to the stability of the water‐table shape. Using these results and extending Boussinesq's usual transient‐state approach, SIDRA, a theoretical model in which soil vertical heterogeneity is taken into account, has been elaborated and applied to simulate by finite differences hourly water‐table levels and drain flow rates. The paper compares observed and measured values of the winters of both 1980–81 and 1985–86.

A procedure has been developed to increase irrigation efficiency by estimating probabilistic irrigation requirements for lowland rice cultivation. The procedure uses a water balance equation with random components to maintain minimum desired water levels in paddy fields at the end of each irrigation period. The procedure estimates weekly pan evaporation and rainfall at different probability levels, which are then used to estimate weekly irrigation requirements through the water balance relationship. The method has been applied to the Kalawewa irrigation scheme in Sri Lanka. Different statistical transformations were used to normalize observed weekly rainfall and evaporation data and to describe their variations. The power transformation was best able to transform the weekly data to normality. Comparison of the use of the model and current system practices shows that a significant amount of water can be saved even when the system is operated at high probability levels.

The Al‐Hassa irrigation system, which consists mainly of open concrete canals with different shapes and sizes, is complex in nature due to the presence of features such as gates, bottom falls, and junctions. The distribution of water through such a network is more complicated due to time‐dependent inflow from the springs and reservoirs into the system. In order to decide gate‐operating policies for irrigation scheduling purposes, the unsteady flow phenomenon used throughout the system to simulate depth and discharge at various reaches with time was studied. The applicabilities and limitations of various models for approximating the solution of Saint‐Venant equations were discussed. The applicabilities and limitations of various unsteady flow packages were also reviewed considering Al‐Hassa network configurations. Among all the available packages, the dynamic wave operational (DWOPER) model developed by the National Weather Service was updated, and hydraulic equations on features such as junctions with distributaries, gates of submerged and free‐flow types, and bottom falls were introduced. Other features, such as interactive capability and use of subsystems, were also added. The modified version of DWOPER is known as the Channel Network Model. Parameters such as gate coefficients and Manning's n‐values of the channel network model were calibrated. Depth and discharge at various reaches of a subsystem were simulated and compared with the observed values.

An analytical solution is derived for a two‐dimensional soil with a sloping surface under steady and water‐saturated flow conditions. The soil was assumed to consist of several layers, each horizontally stratified. The lower layer was assumed to extend to a great depth. Each layer was considered anisotropic in nature where the hydraulic conductivity in the vertical (κ) and the horizontal (ξ) directions are dissimilar. Potential and stream functions are obtained and several flow nets are presented for two‐layered soils with varying degrees of anisotropy. The range of values chosen was $\xi =(1/25)\kappa -\xi =16K$ and equivalent hydraulic conductivities for two soil layers $(K_1/K_2)$ were 1:1, 1:10, and 10:1. The results illustrate the significance of the degree of anisotropy of each soil layer on the water flow pattern, the relative flow rate, and the volume of water passing through individual soil layers. The presence of an anisotropic lower layer did not influence the relative flow rate entering (or leaving) the soil. Moreover, for most cases, the location along the soil surface which separates seepage into and out of the soil was not influenced by the degree of anisotropy of the infinitely thick lower layer.

Annual streamflow records for 124 stream gages in and near Idaho are examined to determine four annual flow statistics: the mean; the standard deviation; the skew coefficient; and first‐order serial correlation coefficient. Using step‐wise regression analysis, the mean and standard deviation are related to the basin characteristics of drainage area, mean annual precipitation, and percent forest cover, with the data regionalized geographically. Two sets of equations for north‐central and southern Idaho provide the best predictive results, with the equations for north‐central Idaho yielding multiple correlation coefficients in excess of 0.97. For the skew and serial correlation coefficients, maps of generalized regional values are prepared by the application of kriging theory, with the resulting maps illustrating the spatial variability of these statistics. The developed equations and maps can be used to estimate annual flow statistics at ungaged locations throughout the state.

An analytical and experimental program was conducted to study the deflection and load‐carrying capacity of small‐diameter corrugated plastic drain pipes. The pipe samples were buried in different soils with various compaction conditions around the pipe. Measurements were taken of the vertical deflection and the pressure around the pipe under a wide range of surface loads. It was found that the most important parameters governing the pipe deformation are the pipe stiffness and the type and degree of compaction of the soil around the pipe. The variation of the modulus of elasticity of the pipe with deformation should be taken into account in pipe deflection prediction. This factor is particularly important in the case of small‐diameter pipes buried in loose soil. The pipe stiffness was found to deteriorate under cyclic loading and unloading. The measured lateral pressure distribution was found to be almost uniform, which departed from the simplified parabolic assumption.

A process that uses the field‐scale model DRAINMOD to simulate the hydrologic response of a watershed to peat mining is presented. An eastern North Carolina watershed has been proposed as the site of a peat mining project. Within the watershed are several distinct soils, land uses, and drainage characteristics. Land use, drainage, and even soil characteristics change as peat soil is mined and reclaimed. The hydrologic response of this watershed is determined for each year of the proposed mining project by combining the field hydrology model with a simple reservoir model, a spreadsheet program, and a statistical program. Results show that peat mining alone increases the annual runoff volume and peak outflow rates. However, by mining land in small sections, by reclaiming the land for agricultural and forest uses, and by installing water retention reservoirs, the annual runoff and peak daily flows from the watershed can be reduced to the magnitude of those presently occurring on the unmined site.

Landsat Multispectral Scanner System (MSS) data in conjunction with the unsupervised classification technique of Earth Resources Laboratory Application Software (ELAS) were used to determine land use/land cover classifications. The Landsat computer compatible tapes (CCT) for February 9, 1976 were analyzed to spectrally classify unique land use/land cover conditions within the Econlockhatchee (Econ) River basin, Florida. The results showed that the scatter diagrams of Band 4 $(0.5-0.6\mu m)$‐Band 7 $(0.8-1.1\mu m)$ and Band 4‐Band 6 $(0.7-0.8\mu m)$ can be utilized as well as the traditional Band 5 $(0.6-0.7\mu m)$‐Band 7 scatter diagram approach for classifying land use/land cover. Both the zoom transfer scope and the geographic information system have been demonstrated to be very useful tools for land use/land cover classification of Landsat data. The Landsat data can be successfully used to monitor the USGS land use/land cover Level I, and the cost and time requirements for the Landsat approach are much less than for the conventional method. Another benefit of Landsat data is that new data are periodically available for updating the land use/land cover information.

A simple device to measure discharge in sewers and drainage channels is described. The unit can be quickly fixed and removed for short‐time use in circular channels. Its major advantages include low cost, reading precision, insensitivity to backwater submergence, and rapid installation in running water. A disadvantage is its limited use in terms of time whenever the water contains significant undissolved matter; the unit should be removed if it is not being supervised, since flooding or clogging might otherwise result. The governing equation for discharge as a function of approaching flow depth is established, and several recommendations for its practical use are given.

The temporal distribution of an irrigation water delivery and demand ratio was used to analyze the performance of an irrigation water delivery system in the Bhakra Canal Command in India. A high degree of mismatch was found to exist between water demand and supply. Based on historical canal deliveries, agroclimatic data, and crop production with dated inputs, yields of wheat, a major irrigated crop of the region, were simulated over a period of 20 years. It was found that crop production was constrained by 34% (20‐year average) due to unfavorable water delivery characteristics. An evaluation was made of introducing auxiliary storage at the farm outlet level to modify the water delivery schedule. Based on the increase in crop yield due to improved distribution of water supply delivery and the cost of auxiliary storage (including the cost of pumping), it was found that auxiliary storage could be used to considerable economic advantage.

For the purpose of irrigation and water resources planning, it is important to know the water loss for a drainage basin. Unfortunately individual measurements of elements of the total water loss are not realistic, at least for the large watersheds studied in this research. Based on the water budget approach, annual water loss series are formulated in this paper. A modeling technique that includes the homogeneity test of data and the best model selection is developed to fit the water loss series by a stochastic process. The results of this study reveal the existence of data nonhomogeneities in the annual water loss series from the Ohio River Basin, which requires adjustments before the mode! fitting by a stochastic process. The selected best model by the criterion of the parsimony of parameter was successfully used to forecast the regional water losses based on the proposed procedure.

The solution for accumulated infiltration using the Green-Ampt equation requires an iterative solution. By using a power series approximtion to a logarithmic term, an equation has been developed to directly calculate the accumulated infiltration for nonuniform soils. A second equation developed primarily for computer models predicts the potential change in the depth of infiltration for discrete time steps. The expression is relatively simple and may be easily programmed for use in hydrologic models. The maximum error resulting from the power series approximation is 8% and will usually be much less. These solutions may be used by engineers and hydrologists to predict infiltration and runoff for vertically nonuniform soils without a time consuming iterative process.