Journal of Irrigation and Drainage Engineering

Since 1981, the Sri Lanka Government has been testing a different approach to delivering irrigation water to its numerous small‐scale farmers. Instead of conventional open‐channel rotation irrigation with water controlled by government organizations, a 367‐acre (147‐ha) pilot project has put each farmer in control of his own water supply using a limited‐rate demand irrigation schedule. This system conjunctively utilizes sloping canals, on‐stream regulating reservoirs, automatic float‐controlled canal gates, level‐top canals, and buried concrete pipelines with float valves to maintain low pressure. Discussed are construction costs and materials, the four cropping seasons evaluated, and the advantages and disadvantages compared to conventional irrigation. Current data show that: an adequate and equitable water supply can be achieved and sustained; crop production can be increased from 8 to 20 bushels/acre (160 to 400 kg/ha); the potential exists for reducing water use below that of conventional irrigation; and that farmer contention is nearly eliminated. Project cost was about 5,860 rupees/acre [$325/acre ($810/ha)] compared to 3,350 rupees/acre [$185/acre (465/ha)] for the conventional system. The resulting incremental increased cost is about 75% at the distributary channel level but about only 7–10% of total project development costs.

This paper deals with the management of groundwater in Kansas through the statutory mechanism of the groundwater management district (GMD). A description of the location of water in Kansas and of relevant Kansas law is followed by a short discussion of the history of the development of the law establishing GMD's and by a description of the location of these GMD's. The paper then describes the powers of GMD's, discusses how GMD's have used these statutory powers, and raises legal questions about these powers. Lastly, some innovative measures being taken by GMD's are discussed.

Field conditions have been reproduced in the laboratory in order to investigate the fundamentals governing the mechanism of clogging of recharge wells. Dosing with water of controlled quality and temperature, containing different types of added suspended solids of know size, with concentration in the range 0.5–250 mg/L was carried out in 45° segmental perspex models simulating confined aquifer conditions. Both filter packed and nonfilter packed wells were tested. It was found that, the lower the concentration of the suspended solids in the recharge water the greater the weight of solids required to clog the well. The filter pack has been clearly established as a major factor in controlling the clogging speed.

The flow pattern resulting from a circular cone immersed in a rectangular channel is investigated under critical flow conditions. The apparatus may be used for both permanent and mobile discharge evaluation in open channels. Owing to the low weight, the high precision of finishing, and its reasonable price when compared to the conventional structures, the modified Venturi Channel may be regarded as a useful instrument. The circular cone is particularly well suited to watercourses in which discharge spectrum is considerable, thereby resulting in moderate approaching flow depth variation. Its rating curve is investigated by accounting for streamline curvature effects. Experiments corroborate the theoretical predictions and indicate that the flow characteristics are governed by the Froude similarity law.

A method for determining width and depth of the wetted soil volume under an emitter is described. The proposed method is tested using computed and experimental results from a plane flow model. A procedure for computing optimal emitter spacing based on the geometry of the wetted soil volume and on the cost of the lateral is demonstrated using computed results from a cylindrical flow model.

The effects of land clearing and drainage as well as effect of drainage system design and management upon hydrologic and water quality parameters were determined. The most dramatic effect of agricultural land development on hydrology is the 2–3 fold increase in peak runoff rates. However, there is little effect upon total water efflux. Land clearing for agriculture does significantly increase N and P efflux in drainage water with the magnitude of the increase being dependent upon soil type. Design of the drainage system, particularly with regard to drain spacing and intensity of surface drainage, can have a large influence upon the proportion of outflow that occurs via surface runoff which is fast and that which leaves the field more slowly via subsurface flow. Improvement of subsurface drainage can result in a 10‐fold increase in the ${\mathrm{NO}}_3‐N$ efflux from some soils. However, the increase in ${\mathrm{NO}}_3‐N$ efflux with improved drainage can be partially offset by utilizing controlled drainage which reduces ${\mathrm{NO}}_3‐N$ efflux. Controlled drainage can result in an increase of P loss in drainage water.

A computer model for the simulation of canal operation was developed. The model is applicable for any nonbranching canal system composed of a series of channels separated by control structures. The programming language used was BASIC, a language suitable to most microcomputers. The Delta Field Division Canal of the California Aqueduct was used for an example simulation and verification. A comparison of data computed by the model to observed data indicated good agreement.

In 1982, 405 measurements of the subsurface drainage water quality parameter electrical conductivity (EC) in dS/m were collected. The data were obtained from 15 subsurface drains on 9.3 ha (23 acres) of irrigated agricultural land at Fallon, Nevada. The temporal and spatial variabilities of EC were studied using time series concepts. Autocorrelation functions (ACF) were used to evaluate the magnitude of temporal and spatial variations of EC. Results suggest that an 11‐week period is the maximum time interval for sampling and that the sampling spatial interval of 36.6 m (120 ft) is too large. Autoregressive integrated moving average (ARIMA) models for both temporal and spatial structures were established through the Box‐Jenkins time‐domain modeling process. The degree of uncertainty of the forecasts were tested using after‐thefact forecast procedures. These models can be used for various purposes such as forecasting future values and determining the transfer function, which provides a way to relate water management plans to water quality control.