Translating a risk-based land-use planning issue to a decision making tool using simple GIS approaches

This paper presents the use of simple GIS approaches to translate a detailed risk-based decision framework for on-site-sewage-treatment-facility siting, design and management into the development assessment process. In 2001 the Gold Coast City Council and Queensland University of Technology collaborated in the development of a detailed risk-based approach to the siting-design and management of on-site sewage treatment systems (Septic and aerobic home sewage treatment systems). Within the Gold Coast City area, some 16,000 properties rely on on-site sewage treatment. Studies indicated that about 9,000 of these are septic tanks and that a high proportion of these do not operate to the required standard due to a combination of design, siting and maintenance failures. These data and the increasing recognition of the ecosystem services provided by the Gold Coast hinterland and waterways indicated the need for greater rigour in assessment and management on-site sewage treatment systems. To do this, a risk-based approach was developed that required translation into the development assessment framework. The GIS (MAPINFO - mapbasic) tool developed interrogates a series of existing maintained layers to derive on-site risk-levels for a given parcel of land based on the science from the studies. This tool connects with planning documents and codes that delineate the level of information needed from the applicant to address the identified risks. The tool provides a quick indication of the risks for the assessment officer, allowing information requests to be produced consistently. It is designed to work with layers that the Council has agreed to maintain rather than maps derived during the study. Among the relevant maintained layers are the waterways, geology, soils and slope. In addition, the tool connects with other layers that can assist with the interpretation, such as existing soil data from nearby sites. This approach leads to consistent and science-based approach to development assessment.