New Zealand Journal of Agricultural Research abstracts

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Hydrological approaches to the delineation of critical-source areas of runoff

M. S. Srinivasan

R. W. McDowell

AgResearch Ltd
Invermay Agricultural Centre
Private Bag 50034
Mosgiel 9053, New Zealand
m.srinivasan@agresearch.co.nz
richard.mcdowell@agresearch.co.nz

Abstract   Five hydrological approaches, ranging from empirical to physically based, were applied in two headwater catchments (Silverstream and Glenomaru) in Otago, New Zealand, to delineate the critical-source areas (CSAs) of runoff, the areas that are directly linked to contaminant transport to surface waterways. Comparison of observed and simulated flows for selected rainfall events indicated that in one catchment (Glenomaru) the empirical approaches performed better than physically-based approaches, while the converse was true in the other catchment (Silverstream). However, spatial mapping of simulated CSAs indicated that the approaches failed to recognise areas where subsurface flows can potentially emerge to the surface as seeps and springs on steep hillsides bordering the valleys. The approaches were also evaluated based on the availability and processing times of input data, representation of hydrological processes, reliability of simulations, likely economic impact, and the ease of implementing alternative management on the CSAs identified. Due to minimal input data needs, minimal likely economic impact, and ease of CSA management, empirical approaches may prove to be the most useable approaches. Process-based approaches simulated unconnected and poorly manageable CSAs that if managed would have a negative economic impact. Economic analysis based on CSAs simulated using the empirical approaches indicated that by managing CSAs to mitigate phosphorus losses, significant decreases in phosphorus losses on a catchment scale can be achieved without any loss in profitability, or even a gain. However, we concluded that these approaches should be examined further and the simulated CSAs validated to allow a better linkage of sources of contaminants and runoff at a catchment scale.

Keywords   critical-source areas; hydrology; modelling; rainfall-runoff processes

A06059; Online publication date 24 May 2007; Received 31 October 2006; accepted 12 March 2007

New Zealand Journal of Agricultural Research, 2007, Vol. 50: 249—265
0028—8233/07/5002—0249 © The Royal Society of New Zealand 2007

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