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Urban Salinity

Murrumbidgee Catchment Management Authority
Urban Salinity Assessment Report
Narrandera

Executive Summary

Narrandera is one of twelve townships in the Murrumbidgee Catchment participating in the Local Government Urban Salinity Action Project, which is designed to provide local government with information to manage urban salinity. In Narrandera, progress towards a better understanding of the nature and extent of urban salinity will be achieved through the installation of groundwater monitoring network.

The major focus of this study is to produce maps from bore water level data, and review the location of urban salinity damage in relation to areas where aquifers are discharging groundwater. Other factors driving salinisation were also examined such as the preferential development of perched aquifers due to land clearing (controlled by landscape features), the spatial distribution of aquifers characterised by low hydraulic conductivity (e.g. clay-rich material) and the identification of potential fault-controlled discharge areas. Landscape (slope,curvature) and hydrogeology (hydraulic conductivity – GWFS maps) datasets were therefore examined separately and compared with the location of urban salinity damage sites.

Urban water management practices (e.g. irrigation, leaking storm water and sewerage systems) and urban infrastructure design (e.g. causing constrictions to surface and groundwater flow) were also likely to be contributing to urban salinity in Narrandera. A study of these datasets was beyond the scope of this investigation.

A study of landscape information to assess perched aquifer development in Narrandera was limited to an interpretation of slope and curvature information produced from a high resolution digital elevation model. Urban salinity damage was noted to be associated with low slope (less than two degrees) and generally concaveareas The critical parameters interpreted to be controlling the location of the urban salinity sites (based on limited information) is the low hydraulic conductivity of clay-rich sediments in concave areas of the landscape.

Geological structures may be exerting an influence and requires further investigation. The role of groundwater and urban water management practices in the development of urban salinity is not known due to a lack of waterlevel information and require further investigation.

Data collection and interpretation - construction of water level and groundwater management maps

• Collect and interpret the Murrumbidgee CMA urban salinity drilling water level and quality information.
• Collect bore construction and use (e.g. aquifer screened and monitoring/pumping status) information for Narrandera shire council bores to allow water level and quality data to be included in the production of maps.
• Conduct FLAG modelling.

Future work

• An assessment of the design of existing urban infrastructure and effects of urban water management practices, including salinity mitigation measures such as; rubble pit removal and revegetation projects is beyond the scope of this project. It is recommended that urban infrastructure datasets, and areas currently targeted for remediation or further development are reviewed in the context of an interpretation of water level and quality data collected from the Murrumbidgee CMA urban salinity piezometers. This will assist both the planning and assessment processes by providing the extent of high priority groundwater recharge 'minimisation' areas.

• Water level maps should be constructed from bore information in the Narrandera urban watershed to provide catchment scale information on groundwater levels and water quality that can be incorporated into local government water management plans (e.g. Urban Salinity Management Plans, Integrated Water Management Strategy Plans).

• Conduct a quarterly or biannual review of the monthly data collected from the Murrumbidgee CMA urban salinity monitoring bores. These temporal data combined with rainfall and evaporation information can be used to construct a water balance for Narrandera and therefore better understand recharge to the groundwater system from the urban environment.

• Expand the water quality dataset (electrical conductivity - salt content/concentration) by conducting EC1:5 analyses on the drill core from the Murrumbidgee CMA urban salinity drilling and/or geophysically logging the boreholes with an induction conductivity tool (e.g. EM39) to understand thedistribution of salt with depth.

• Urban salinity damage sites could not be assessed in relation to existing urban infrastructure (e.g. road design, 'leaking' stormwater and sewer systems) that could be causing, as well as exacerbating, the problems. This was due to this assessment being outside the scope of this investigation. It is recommended that this takes place in the next stage of the urban salinity review in Narrandera.

• Minimise urban salinity problems across the Narrandera urban watershed through the adoption of  'best'  urban water management practices to reduce groundwater recharge by (1) controlling and phasing out the use of rubble pits and underground tanks/wells to dispose/store waste water (2) reviewing surface and sub surface drainage systems to ensure there is minimal leakage to groundwater, and with respect to surface systems; gradients are transporting water in a timely manner that limits evaporation and (3) redesigning sub surface and surface drains to incorporate vegetation options in water management.

CONTACT US

141 East Street Narrandera
NSW 2700

T (02) 6959 5510
F (02) 6959 1884
council@narrandera.nsw.gov.au