Abstract
Abstract. Contributing Catchment Area Analysis (CCAA) is a spatial analysis technique developed and used for estimation of the hydrological connectivity of relatively flat catchments. It allows accounting for the effect of relief depressions on the catchment rainfall-runoff relationship which is not commonly considered in hydrological modelling. Analysis of distributed runoff was based on USDA runoff curves numbers (USDA, 1986), which utilised the spatial information on land cover and soil types, while CCAA was further developed to define catchment area contributing to river discharge under individual rainfall events. The method was applied to the Southern River catchment, Western Australia, showing that contributing catchment area varied from less than 20% to more than 60% of total catchment area under different rainfall and soil moisture conditions. Such variability was attributed to a compensating effect of relief depressions. CCAA was further applied to analyse the impact of urbanisation on the catchment rainfall-runoff relationship. It was demonstrated that in addition to an increase in runoff coefficient, urbanisation leads to expansion in the catchment area contributing to the river flow. This effect was more evident for the most frequent rainfall events, when an increase in contributing area was responsible for a 30–100% rise in predicted catchment runoff.
Highlights
Prediction of the rainfall-runoff relationship in flat catchments and under land use alteration is challenging
The analysis of the model outcome was based on simultaneous estimation of the areas Aa and Ab contributing to the river flow under two scenarios a and b and associated runoff Qa and Qb generated from those areas
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Summary
Prediction of the rainfall-runoff relationship in flat catchments and under land use alteration is challenging. Hydrological connectivity concepts are an emerging approach for the analysis of runoff generation (Bracken and Croke, 2007). It allows accounting for landscape connectivity and/or hydrological connectivity, defining various aspects of the water transport from one part of the catchment to another and overall contributing to catchment runoff. The concept of a “catchment contributing area” used in this study is closely linked with a term “hydrologic connectivity” as suggested by James and Roulet (2007) They defined it as hydrologically relevant spatial patterns of properties (e.g. permeability or soil or land cover) or state variables (moisture content of soil) that facilitate flow and transport in a hydrologic system. This definition is broadly in agreement with that by Bracken and Croke (2007) used in their conceptual framework describing relevant “landscape position” and “delivery pathways”
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