Implementing the Riparian Particulate Model to assess the impact of Watercourse Project in the Myponga River Catchment

Abstract

Riparian buffers are vegetated strips of land which separate surface waters from areas which contribute water and constituent runoff. They play an important environmental function of reducing pollutant inputs to streams. In the Myponga River Catchment of the Mount Lofty Ranges in South Australia, considerable work was undertaken between 2000 and 2007 to construct and revegetate riparian buffer zones in order to mitigate pollutant loads to streams. This paper describes how the Riparian Particulate Model (RPM) (Newham et al, 2005) can be used to investigate the potential benefits of the work in improving water quality in the catchment. The RPM model is a simple conceptual model of particulate trapping in riparian buffer zones. It simulates the particulate trapping capacity of riparian buffers through settling, infiltration and adhesion. The RPM runs at a daily time interval and operates as a filter module within the Source Catchments modelling framework (eWater CRC, Australian). Source Catchments is a node-link catchment scale model for simulating hydrology and constituents impact in catchments. This paper reports development and application of the RPM in the Myponga Catchment. Development of the RPM in Source Catchments involves three stages: runoff generation, constituent generation and filtering. More specifically; •building the rainfall-runoff model using SIMHYD •building the constituent generation model using event mean (stormflow) concentration and dry weather (baseflow) concentration. These are used to calculate sediment and nutrient loads from flow of streams in the Myponga River Catchment •developing and implementing the RPM model to simulate the trapping of coarse and fine particulate in riparian buffer zones. The Myponga RPM was applied to assess the likely impacts of riparian buffer establishment over the period 2000 to 2007. The model predicted that the amount of fencing and revegetation of the watercourses undertaken in the catchment (around 10%) would have reduced the overall sediment load by approximately 12%. In certain areas of the catchment where more extensive works were undertaken, sediment loads would have been reduced by up to 54%. This indicated that the Myponga Watercourse Restoration Project had made improvements to water quality in the catchment. This paper reports semi-quantitative predictions of potential particulate trapping by grass riparian buffers at a catchment scale. These predictions provide valuable information to the SA EPA and the AMLRNRM (Adelaide and Mount Lofty Ranges Natural Resources Management Board) in their future riparian buffer zone establishment and restoration projects. Furthermore, development of riparian filtering models such as the RPM can be beneficial for government agencies to assess the benefits of on-ground work and to target remedial action.