| Popis: |
Recharge to the aquifer through seepage from irrigation canals is often quoted as one of the main causes for waterlogging in Pakistan. In the design of drainage systems to control this waterlogging, rules-of-thumb are often used to quantify the seepage from canals. This paper presents the option to use a groundwater model for a more detailed assessment. Groundwater models can assist in evaluating the effect of recharge reducing measures such as interceptor drains along irrigation canals and lining. These measures are commonly aimed at reducing the drainage requirement of adjacent agricultural lands. In this paper the hydrological concepts with respect to leakage from irrigation canals and interception by interceptor drains are presented. A good understanding of these concepts is critical for the proper application of numerical groundwater models and for the correct quantification of model parameters. Key hydraulic parameters are the infiltration resistance of the bed and slopes of irrigation canals, the drain entry resistance of interceptor drains, hydraulic conductivity and hydraulic resistance of soil layers and equivalent depth of groundwater flow. The paper shows how the hydrological concepts can be transferred into model parameters for the widely used groundwater modelling package MODFLOW. Most concepts, however, can also be applied in other modelling packages. The presented hydrological and modelling concepts have been applied in a numerical model for the Fordwah Eastern Sadiqia project, Pakistan. This model application is reported in a separate paper. |
