Combining GIS ArcHydro tools with a distributed HEC-HMS model for the Upper Waimakariri River Basin: A dissertation submitted in partial fulfilment of the requirements for the degree of Masters of Applied Science

Abstract

A distributed hydrologic model within the HEC-HMS modelling software was applied to the upper Waimakariri catchment as study area. The model was parameterised for the ModClark direct runoff model by deriving input parameters using GIS analysis and applying ArcHydro and other GIS tools. The ArcHydro GIS datamodel structure was explored and a hydrological geodatabase for the study area created.

Radar reflectivity and rain gauge data for the rain event on the 8./ 9. January 2004 were obtained. The radar data were calibrated with the rain gauge data and processed for modelling input. The data had to be converted into DSS format, the HEC-HMS specific data storage format for rainfall grids. In GIS a grid was superimposed on the catchment area containing catchment information for each grid cell such as flow length to sub catchment outlet, SCS curve number and the cell co-ordinates. A method was developed to derive the information and extract a catchment characteristic file in ASCII format for direct model input. The SCS curve numbers were originally developed for agricultural catchments in the United States. Several assumptions had to be made and local data analysed to assign SCS curve numbers to the study area. All required model input data was acquired and processed. Although there was a number of formatting and model configuration issues, a first model run was performed successfully. No calibration or optimisation was carried out, but the results indicate that the SCS curve numbers were generally too low and require modifications.

The ArcHydro tools and data model were useful for deriving general hydrological modelling parameters for manual model input. For the HEC-HMS ModClark model in particular, no direct automatic data transfer was possible with existing software. The opportunity exists for future users to overcome this by writing Visual Basic programs. It is expected that more utility programs and routines will be available over time, although they might not be compatible to the New Zealand co-ordinate system.