灌溉排水系统工程

Policy intervention in the management of community based water storage structures (CBWS) depends on identifying the factors governing collective action and institutions. Institutional factors not only have a direct bearing on the functioning of CBWS but also often interact with physical and technical factors to influence their sustainability. The present study has examined these issues taking sustainability of CBWS as a function of two components, financial viability and CBWS functionality to draw policy implications in Indian context. Data collected from field surveys revealed that Panchayati Raj Institution (PRI) functionality, perception about change in water collection time and number of households served by the water resource significantly affected financial viability of CBWS. The CBWS functionality was, similarly, found to be significantly affected by factors like accessibility and use restriction with respect to the CBWS. PRI functionality in respect of community resource management, therefore, need to be addressed through better representation of women and weaker section of the community in management of these resources as these sections of society are largely affected by their management. Factors such as use restriction of community water source which affected the physical status of the resource and catchment land use and storage to catchment ratio, which affected operational status of the source, are critical while designing location and size of the water resource such as pond.

This paper presents efficient closed form expressions, based on the discrete outflow distribution, to compute the friction head loss and the friction correction factor in center-pivot laterals divided into several reaches. Since such formulas cannot be found in the literature, we develop these expressions based on the discharge required by each sprinkler and each reach to irrigate an annular area.

These expressions can be used in center-pivot laterals with and without end gun sprinkler and with and without closed outlets at the beginning of the lateral. Moreover, these expressions also allow to compute the head loss between the last outlet and the end gun sprinkler usually neglected by another investigators.

These expressions were developed for center-pivot laterals with: 1) a single diameter and with constant spacing between sprinklers along the lateral and 2) a single diameter and a lateral divided into several reaches where the spacing between outlets is constant but the spacing is different in each reach.

This apparently complex method is easy to implement computationally and easy to understand. It can be applied using the Hazen-Williams, Scobey or Darcy-Weisbach friction loss equations.

An application using the Hazen-Williams equation to compute the friction head loss for a center-pivot divided into three reaches is presented. The results obtained with the method of the discrete outflow distribution are compared with the method of the continuous outflow distribution.