Storm water is all forms of precipitation – rain & snow. In a natural setting only a small percentage of rain becomes surface runoff, but as development occurs this percentage increases. Surface runoff usually flows into the nearest stream, river, lake, or wetland and in the case of Tamil Nadu, into the numerous interconnected irrigation tanks that were built between the 6th and 10th centuries.

Storm water management involves the control of this surface runoff. The volume and rate of runoff both substantially increase as land development occurs. Construction of impervious surfaces, such as buildings, paved areas within the landscape and roads prevent the infiltration of rainfall into the soil and management of stormwater runoff becomes necessary to compensate for possible impacts of impervious surfaces. Some of these impacts include a decreased groundwater recharge, increased frequency of flooding, concentration of flow on adjacent properties, and damage to buildings and utility infrastructure.

Since we consider rain runoffs as a resource that provides benefits such as groundwater recharge, we work at retaining it as much as possible in trenches, pits or rain gardens, increasing its opportunity to percolate into the soil. However, Infiltration is many times limited by the soil structure of the areas where infiltration will be directed or targeted. As soils have varying percolation and water holding capacities, which influence both the amount and rate at which water can be infiltrated into the ground, it becomes critical to consider an approach that takes into account not just the possibility of percolation but also decreasing impervious surfaces, create rain gardens, have active rain water harvesting and reducing building footprint