Ipswich City CouncilWaterwaysErosion and SedimentErosion - The Creeping Catastrophe Erosion is recognised as the greatest land degradation issue facing rural Australia. However with proper understanding and application of good land management practices, it is perhaps the most preventable form of land degradation. Erosion is basically the dislodgment and movement of soil from one location to another by wind or water. There are five main types - raindrop splash, sheet erosion, rill erosion, gully erosion, streambank collapse, and tunnel erosion. More than one type of erosion can be involved in any erosion problem. Surprisingly large quantities of soil can be lost with erosion. One centimetre of soil lost from a one hectare surface area is equivalent to approximately 100 cubic metres of soil being removed - weighing about 100 ton's. Losses of 5 to 10 cm of top soil from many hectares are fairly common during intensive summer rain. In fact, an average 10 ton's per hectare per annum soil loss from cultivation land is considered ‘acceptable'. Erosion risk is increased markedly when the soil is in a bare, cultivated condition. Within the Bremer River Catchment, Deebing Creek sub-catchment (3457ha), located south of the Ipswich urban area, is somewhat different to the other twelve sub-catchments. It consists largely of solodic soils which are highly erosive. Areas of cleared land left uncovered for the construction of residential buildings is the major contributor to this problem. This sub-catchment requires particularly stringent management strategies to reduce future erosion and sedimentation of Deebing Creek. Erosion is also considered to be a serious problem in the Mid and Lower Warrill Creek sub-catchments. Irrigation of agricultural land not only exacerbates erosion but also increases the occurrence of soil salinity. Salinity occurs when mineral salts within the soil are carried to the surface with rising ground water. Salt is then carried into the waterways with soil particles and rain water run-off.
Sediment Sediment or soil particles can consist of gravel, sand, silt and clay. The amount of sediment entering our creeks and rivers has substantially increased as a result of the catchment being cleared for agricultural land, soil disturbance during forestry operations, urban and industrial development and bare areas such as gravel roads and stock paths. It is the sediment that runs off into our waterways that causes our rivers to become brown, dirty and unhealthy. The river becomes out of balance and cannot cope. Creeks and rivers have responded to the changes in the catchment by changing their shape. Streambank erosion is often a symptom that the waterway is responding to a range of changes, and as a result can deliver huge amounts of soil directly to the water. The main contributors to sediment in the Bremer River and its tributaries are:
Suspended sediments have a major impact on the aquatic ecology, altering habitats for aquatic organisms and reducing light penetration for plant growth. Water quality is also degraded due to the addition of pollutants such as nutrients, heavy metals and microbes, attached to sediment particles. Sedimentation is arguably one of the most devastating impacts on our waterways requiring immediate attention.
In The Bremer River Catchment A land degradation survey of the catchment by the Department of Primary Industries in 1979 concluded that land degradation from over clearing of the vegetation, and inappropriate cropping and grazing practices, have been identified as the largest problem facing land managers in the Bremer River Catchment with more than 41 % of the catchment considered degraded. The Bremer River Catchment Management Strategy identifies erosion and sedimentation as a high priority issue within the Bremer River Catchment. The community has identified widespread sheet and gully erosion on agricultural land, gully erosion on streambanks, a lack of natural vegetation on riparian zones and a lack of cover in pasture lands as a few of the priority issues for the catchment. With increasing urban development occurring within the catchment, the ongoing control and reduction of silt and nutrients accessing our waterways is an important issue.
Management and Control of Erosion and Sediment Sediment and erosion problems occur throughout the entire catchment with the majority of sediment coming from cleared agricultural land within rural areas. However, when considering management strategies it is important to realise that urban areas contribute more than twice as much sediment per hectare during rain periods. Instruments to assess the amount of sediment coming from urban areas and construction sites have been set up along Mihi Creek within the Brassall area. Data collected from these sediment samplers will be used to develop and implement effective management plans for the control and management of sediment loads from developing and existing urban areas. Other management and control techniques (existing and proposed) include:
Last Updated 4 Jan 2012 |
 Print this page |  Contact us |  News Feeds
| Copyright © 2012 Ipswich City CouncilPrinted From: http://www.ipswich.qld.gov.au/residents/healthy_lifestyle/waterways/erosion_and_sediment |