Site selection of Micro-catchment water harvesting systems at basin scale, with intersecting methods in GIS (a case study; NazlouChay Basin, Western Azerbaijan)

Iran and accordingly the study area due to placing on the dry belt region of the world are always faced with the drought phenomenon and shortage of rainfall. Accordingly, the efficient use of water and the management of these areas are integral component requirements of such areas. Precipitation pattern in arid areas occurs as storms with the high intensity usually in short time and causing huge runoff in the basin that will carry valuable surface soil and decreasing water infiltration opportunity in the soil. Different techniques of rainwater harvesting from natural lands, improved micro-catchments or agricultural micro-basins will lead to developing sustainable economical agriculture and store runoff into soils, dams, terraces, ponds, ditches, and reservoirs. The study area with 470 mm rainfall and runoff coefficient of 0.26 has the high potential of water harvesting at the basin scale. Previous studies show that lower gammas fuzzy logic values target macro-catchment systems of water harvesting well, but in micro-catchment systems with using fuzzy operators are less researched.
In this research for finding suitable areas for water harvesting, 3 systems including semi-circular bunds, contour furrow, and bench terrace with using GIS in Nazlu basin with 1507 km2 area, of west Azarbijan were investigated. Watershed factors such as climate, physiographic and hydrological factors, six important layers of precipitation, slope, land use, hydrologic soil groups, and drainage and soil depth were selected. For intersecting and making layers dimensionless, Fuzzy logic with trapezoidal membership function and Fuzzy logic with the analytical hierarchical process (AHP) were used for the quantitative and qualitative variables respectively. AND for combining of layers Boolean AND, Boolean OR, Fuzzy algebraic Product, Fuzzy algebraic sum, Fuzzy gamma of 0.1 to 0.9 methods were examined.
The “measure of similarity” is used for comparisons of filed observed and combination outputs. The results show for the crescent bankette and the Gamma-0.9 Fuzzy, this figure equals 0.824 and for counter furrow, equals 0.906. These figures indicate that fuzzy gamma 0.9 has better suitability than other method and also Boolean logic model do not show suitable results. Similarity index in fuzzy logic increases up to 0.9 gamma and returns below 0.9. High Gamma for site selection of Micro-catchment water harvesting systems shows better results. The 30% of the basin is suitable for semi-circular bunds, the 11.5% for contour furrow and 6.3% for bench terrace.
The results show that for determining the locations suitable to micro-catchment water harvesting methods, Boolean methods are less useful due to low precision and the usage of newer methods of gamma fuzzy logic should be considered, instead.