Runoff yield in Bangalore is calculated spatially based on the empirical equation (eq 1) using GIS
Q = C*A*P/1000        ………1
(Raghunath, 1985; Subramanya 2005; Ramachandra et al., 2013, Ramachandra et al 2014)
Where, Q = runoff in cubic meters; C = runoff coefficient (depends on land use of each pixel); C = 0.85 – 0.95 for paved surfaces (Built-up); C = 0.40 – 0.60 for open/agriculture and horticulture; A = area (pixel or catchment) in square meters; P = precipitation as mm

Figure 5.1: Runoff (mm/year) in Bangalore

Runoff (mm/year) is depicted in figure 5.1 and higher surface runoff were observed in the localities with higher paved surfaces.  Water retaining capacity in the catchment is higher dominated by vegetation cover and water bodies, and with this, lower overland flow or surface run-off were observed during monsoon.

Catchment wise water yield analysis indicates that about 49.5% (7.32 TMC) in the Vrishabhavathi valley (including Arkavathi and Suvarnamukhi), followed by 35.2% (5.2 TMC) in Koramangala Challaghatta valley and 15.3% (4.2 TMC) in Hebbal valley and the total annual water yield is about 14.80 TMC.