Application of random walk algorithm into finite element numerical groundwater model for capture zone depiction

Determination of wells' capture zones is one of the most remarkable issues that should be carried out in each aquifer. Methods used for depicting this area has been divided into two simple and complex method. Through the simple one several mathematical equations are used and in the complex approaches, numerical models are applied. In this study, the capture zone of extraction wells in a confined aquifer is determined using random walk algorithm and finite element numerical model. The studied aquifer consists of three extraction wells and one injection well in which the extraction and injection operation are performed for 10,000 days. After the simulation procedure, the groundwater head is obtained. Simulation results show high accuracy which its root mean square error is 0.141 m while this value for finite difference solution is 0.249 m. then the capture zone for each well was depicted individually in two periods of 50 and 180 days. Results showed that the extension of the capture zone for all three wells is toward the part of the aquifer, which has a higher groundwater level than other areas. Also, the results revealed that, in areas of the aquifer that have a higher transmissivity coefficient, the zone is more extended and for the areas with lower transmissivity coefficient, its width decreased and became narrower. In the second well, the width of capture zone in zone 2 and 3 were 302.86 m and 267.46 m, respectively.