Floodplain Management
Management Strategies | Flood Data Mapping
Flooding is a recurring issue in the Alluvial Soils Resource Management Unit on the intensively used lower reaches of the Mitchell and Snowy Rivers. These events cause mass soil loss, stream degradation, damage to infrastructure and loss to agricultural production. Between 1950 and 1992, there have been 63 serious floods on the Snowy River alone. Flood warning procedures were upgraded since the major 1990 flood on the Mitchell River, as an action to prevent loss of stock and structures. However, floodplain management, including planning controls on levee banks and drainage structures, is a contentious and unresolved issue in the East Gippsland region (East Gippsland CaLPB, 1997).
Following heavy rain in East Gippsland in June, 1998, major flooding occurred in the Mitchell, Nicholson, Tambo, Snowy, Brodribb and Bemm Rivers. Other streams in the region also experienced high flows during this time. The cost of flood damage to East Gippsland Water was approximately $225 000. As a result, all high priority flood restoration works have been completed (East Gippsland Region Water Authority 1999).
Flood Data and Planning
The majority of floodplains in the East Gippsland region have been cleared of native vegetation and are utilised for cropping or pasture. These land uses are contributing to the deterioration in the natural riverine, floodplain, and estuarine environments. Within many parts of Victoria and the East Gippsland region, natural processes of upstream erosion and downstream deposition of alluvial material have resulted in many waterways being perched above their floodplains. A characteristic of such systems is a generally low river capacity, resulting in frequent overtopping of natural levee banks (SKM, 1999). In the past, many of these rivers have been subject to "river improvement" activities to improve their capacity to convey flood flows. Such activities include de-snagging, artificial levees, channel widening, and channel straightening. The effect of these activities has been to reduce flood attenuation and increase peak flows and in-stream erosion. These impacts must be balanced against the benefit to some landholders in flood mitigation and drainage improvements.
The main river systems within the East Gippsland region are:
- Mitchell River Basin,
- Tambo River Basin
- Snowy River Basin
- East Gippsland Basin.
Approximately 300 km2 of rural and urban land across the East Gippsland region under public and private ownership is subject to inundation. This does not include land adjacent to the Gippsland Lakes in which a further 390 km2 may be inundated (EGIS 2000, EGCMA Draft Regional Floodplain Management Strategy). The need for floodplain management is recognised in the East Gippsland Regional Catchment Strategy (RCS) that notes the soil loss, stream degradation, damage to infrastructure and loss of agricultural production caused by flood events. Average annual flood damage is estimated to exceed $5.3 million per year and this is believed to be escalating as development on the floodplains and on lake frontages continues for urban, agricultural and infrastructure purposes. Only few flood mitigation works exist to interfere with the natural spread of floodwaters and interaction between the stream and floodplain environments. The floodplains of these basins and the industries that are affected by flooding are described in the Table below.
Areas prone to flooding in the East Gippsland region
Catchment / Floodplain | Area km2 | Land uses | Works on floodplain | Major flood duration (days) | Population |
| Mitchell River | 60 | Residential, Commercial, Horticulture, Dairy Grazing | Private Levees, Floodgates | 3 to 40 | 14 000 |
| Dargo River at Dargo | n/a | Residential, Commercial, Grazing | None | 2 | n/a |
| Nicholson River | 8 | Grazing | None | 3 | 100 |
| Bruthen Flats | 15 | Grazing, Dairy | Limited Levees - both private and public, Floodgates | 2 | 600 |
| Swifts Creek | 3.4 | Residential, Commercial Grazing | None | 1 | 250 |
| Lower Tambo Floodplain | 12 | Grazing | Limited public Levees | 2 | n/a |
| Buchan Floodplain | 2.9 | Residential, Grazing, Timber milling, quarrying | None | 1 | 400 |
| Snowy River | 117 | Residential, Commercial, limited Horticulture, Dairy, Grazing | Levees, floodgates, Drainage Scheme | 2 | 2 550 |
| Cabbage Tree Creek | 19 | Grazing | None | 2 | n/a |
| Bemm River | 5.4 | Grazing, Tourism, Residential | Public and private Levees | 2 to10 days (depends if entrance is open or closed) | n/a |
| Cann River | 26 | Grazing, Residential | Public Levee | <1 | 250 |
| Genoa River u/s of Gipsy Flat | 4.6 | Grazing | None | 1 | n/a |
| Mallacoota Inlet | 29.4 | Residential, Commercial, Tourism | None | -? | 1 000 |
Related Links
Information on Floodplain Management on the East Gippsland Catchment Management Authority website (external link).
The Bureau of Meteorology website provides daily River Height Bulletins (external link) across Victoria.
A wide range of flooplain data can be accessed via MapShare (external link) in the form of an interactive map, using information from DPI/DSE. The Catchment and Water Mapper section provides information on themes such as rivers, 1 in 100 year flood, floodways, and river basins.
References
East Gippsland Region Water Authority (1999). Annual Report 1998/99. Bairnsdale, Victoria.
East Gippsland Catchment and Land Protection Board (CaLPB) (1997). Regional Catchment Strategy, East Gippsland CaLPB.
EGIS (2000). EGIS Consulting. Flood Data Transfer Project (the former) DNRE. (formerly)DNRE/NHT. Victoria.
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