Rainwater harvesting potential for irrigation and groundwater recharge- Gulberg Greens, Islamabad, Pakistan.

Rainwater harvesting (RWH) is the first-rated and cost-effective measure in resolving water crises issue. The monthly mean rainfall data for 31 years (1986 to 2016) was studied to calculate the RWH potential. The study area (Gulberg Greens, Islamabad) was divided according to its intended use for residential farmhouses, public facilities, commercial buildings, public parks, roads, and graveyards covering 573, 207, 47, 190, 212, and 14 hectares (ha) respectively. The RWH potential of each area was estimated using the runoff curve number (RCN) method considering the landscape slope, soil type, land use, and antecedent moisture content. Three alternative landscaping patterns were studied for each farmhouse, having different areal coverage for fruits, vegetables, and land cover. The Blaney-Criddle equation was applied to estimate the crop water requirements of each landscaping alternative. The monthly harvested rainwater volume from each farmhouse was compared to its monthly irrigation demand for each landscaping alternative. The results indicated similar patterns of RWH potential for farmhouses of 0.506, 0.252, and 0.202 ha, with minimum volume in December (0.07, 0.03, and 0.02 million liters (ML), respectively) and maximum volume in July (1.21, 0.66 and 0.51 ML, respectively). The total RWH volume from farmhouses, roads, streets, public parks, public facilities, commercial buildings, and the graveyard was 4608, 2087, 1205, 1665, 530, and 112 MLy−1 respectively. Similarly, the monthly irrigation water demand for the seven months (Jan, Feb, Mar, Jul, Aug, Sep, and Dec) was completely satisfied by the harvested rainwater and for the remaining months (Apr, May, Jun, Oct, and Nov), the demand was fulfilled from 30 to 80%. Furthermore, the annual saving from RWH is around Rs. 500, 245, and 200 thousand for 0.506, 0.252- and 0.202-ha farmhouses, respectively. [ABSTRACT FROM AUTHOR]