4.2.4 Sub-Criteria Standardization?

1.2.4.4 Sub-criteria standardization
The standardization process consisted in conversing cell values of the sub-criteria layers into a common [0-1] scale. The minimum 0 corresponds to the less desirable condition with regards to aquifer recharge with reclaimed water and 1 the most desirable condition. The cell values of all continuous numerical sub-criteria (e.g. slope, soil salinity and unsaturated zone depth) were rescaled using fuzzy linear membership functions. For categorical layers (e.g. soil texture, land use and geology) the categories were first grouped into classes according to their potential for aquifer recharge. Then, they were pair-wise compared using Saaty matrix (Gomez and Barredo, 2005). The resulting values were rescaled linearly
The corresponding formula is as follows:

Where wk is the weights of the sub-criterion k and rik the standardized value of the pixel (i) in the map of the sub-criterion k. Ri varies between 0 and 1 where 0 is the least suitable value for recharging aquifer and 1 is the most suitable value.
1.2.5 Estimation of the required area
To estimate the area required to infiltrate the effluents of SE3 and SE4 we adopted the equation developed by the Environmental Protection Agency of the United States (EPA 1984). The equation considers the bare bottom basin as basins type and it is based on the hydraulic loading rate, the number of wetting/drying cycles and the outflow. The equation is expressed as follow (EPA 1984):
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The hydraulic loading of wastewater L is estimated to be 10% of the hydraulic loading of clean water (Lcw) (EPA 1984). Lcw could be obtained experimentally or using the EPA (1984) following empirical equations (1b). (1b)
Where Kv is the soil hydraulic conductivity. In our study the hydraulic conductivity was obtained by averaging the hydraulic conductivity of the feasible soils for Nabeul-Hammamet aquifer recharge with treated wastewater according to the equation (1c)
Where K is the hydraulic conductivity [cm/hr], i is the index of the soil texture (Fig.4-c), Si is the surface of the soil (i) [ha] obtained from (Fig.4-c), Ki is the hydraulic conductivity of the soil (i) [cm/hr], S is total feasible surface obtained from to the soil texture constraint layer (Fig.4-c). Based on Saxton and Rawls (2005); Raoul Clavet et al., (2003); Rawls et al., (1998) and Clapp and Hornberger, (1978) a Ki value was assigned to each soil texture in Nabeul-Hammamet region (Table.7).
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