Effect of the Construction of Mamloo Dam on Land Subsidence in Varamin Plain

Mamloo dam in Tehran province has been built to meet the needs of agricultural water in Varamin plain, but due to the drinking water supply in Tehran, a limited amount of stored water is supplied to the plain. One of the most important effects of the insufficient supply of surface water in Varamin plain is the reduction of groundwater aquifers and land subsidence. In this study, the effect of the Mamloo dam on land subsidence in the Varamin plain was investigated.

The changes in groundwater level and the unit hydrograph of the plain and quantitative changes of groundwater in the study area of Varamin plain located downstream of the dam were studied and analyzed in two periods before and after the operation of the Mamloo dam.

Based on the results obtained from the selected piezometric network and according to the division of the study area into northern and southern regions, the greatest amount of decline was in the northern part. After the construction of the Mamloo Dam, new evacuation points were created based on the potential maps in the northern and central parts, where the population and agriculture centers were located. In the south, due to the type of geological structure and less alluvial thickness, the emptying of the pores of the aqueous layer has led to subsidence in some areas. Finally, the adaptation of the areas with the greatest decrease in groundwater discharge to the areas with the highest vertical displacement in the southern and central regions in the radar maps was quite clear.

By investigating the results obtained from the analysis of the drop of piezometers in the study area of ​​Varamin plain and the expansion of the number and depth of deep wells in the mentioned plain, the change in the underground water flow regime and the reduction of the aquifer volume are clear. After the construction of the Mamloo dam, the amount of this drop has increased, especially in the lands of the northern part. In addition, the lack of proper planning in meeting the needs of the agricultural sector of the plain, which has a major share in the consumption of water obtained from underground sources, has caused major challenges in the climatic and social conditions downstream of the dam. Due to the construction of the Mamloo dam at the entrance of the Jajrood River to Varamin plain, the level of the water table has decreased over time due to the significant reduction of surface flow to the region. This decrease had higher values ​​in the northern half of the plain and in the areas where the thickness of alluvium is greater. Based on the output of satellite and subsidence maps, the areas that experienced more discharge and drop during the statistical period correspond to the areas with more subsidence in the subsidence maps.