Storm Lateral Runoff Calibration by Direct Hydralic Balances

Storm runoff is usually measured only at the catchment outlet, which restricts hydrological modelling to lumped empirical whole-catchment measures. This defeats physical analysis of the runoff process where the actual catchment has a diversity of permeabilities, slopes and storm intensities. A study of riparian resistance on a suburban reach of the Opanuku Stream in West Auckland demonstrates that stream roughness measurements are highly sensitive to lateral inflows. This means that, provided the mass balance modelling error is negligible, the lateral runoff from the local subcatchment into the reach can be calibrated at the same time as the stream roughness. This residual flow difference between reach inflow and outflow offers a new hydraulic calibration technique to support improved analysis of local storm runoff.