**9. Estimation methods**

In order to maintain the sustainability, the process of ground water recharge is adopted at which the recharge rates are usually difficult to measure. The difficulty in quantifying the rate of ground water recharge has become a tedious process because [13], it is in need to measure the related processes such as transpiration, evaporation and infiltration for achieving balance in the environment. **Figure 5** shows the cycle of water flow [14].

## **9.1 Physical**

For the purpose of estimating the recharge at the ground water table, it is necessary to employ physical methods for determining soil physical principles. The direct physical methods are also incorporated to quantify the amount of water that passes through the soil pores below the root zone. While the indirect methods depend on determining or identifying soil parameters, which is used for measuring the potential of actual ground water recharge. At this method, the quantified ground water denotes that amount of drained ground water during no rain season and if the area of catchment is already known, then the recharge rate could be identified through the base flow itself.

#### **9.2 Chemical**

This kind of method could used while the ground water is found at a deeper zone, where the chemicals like chloride, isotropic tracer [15] are utilized in presence of relatively inert water soluble substance poignant through the soil.

#### **9.3 Numerical models**

The ground water recharge is identified using numerical codes such as Hydrologic Evaluation of Landfill Performance, UNSAT-H, SHAW, WEAP, and MIKE SHE. HYDRUS1D, a 1D programme that is available online. These kinds of codes usually use datas obtained by monitoring climate and soil to determine the amount of

**Figure 5.** *Cycle of water flow.*

recharge to be done. At these numerical models, the flow of water at the vadose zone in the aquifer could be modeled with the consideration of Richards's equation.
