Remedial measures for Soil erosion and Coastal erosion

Remedial measures for Soil erosion and Coastal erosion

Soil erosion

Using trees to control erosion

Trees are often considered to be the universal answer to control soil erosion. Tree roots help prevent landslides on steep slopes and stream bank erosion but they don’t stop erosion on moderately sloping hillslopes.  In forests, the soil surface is usually protected by a layer of mulch from decaying vegetation as well as a variety of surface growing plants. If the soil is bare under the tree canopy from over grazing, vehicles or pedestrians, soil erosion will still occur.

Contour banks and strip cropping

Runoff concentration is managed by structural measures such as contour banks in upland areas, or strip cropping on floodplains. These systems involve a total change in the way a farm is managed.  Runoff systems must be carefully planned. Flow between properties and across roads and railway lines must be coordinated and suit those affected by the changes.

When runoff water can impact neighbouring properties or infrastructure, land owners are encouraged to discuss with their neighbours and seek professional advice.

Approximately 80% of soil lost as a result of poor cover can be trapped in the paddock by contour banks. The banks channel the runoff at low speed into grassed waterways. Good surface cover between contour banks and in waterways will ensure their stability and dramatically reduce the amount of soil deposited in waterways.

On flood plains, strip cropping is used to spread flood flows rather than allowing it to concentrate.

Green cane harvesting

Another measure that maintains soil cover is green cane harvesting or ‘trash blanketing’. When a cane crop is harvested, the leaves and tops of the cane are left on the ground as a ‘trash blanket’. This protects the soil from erosion by raindrop impact. This practice has been widely adopted in many Queensland cane growing districts.

Coastal erosion

Marshes

creation for shore erosion control can be accomplished by planting the appropriate species, typically grasses, sedges, or rushes, in the existing substrate and addressing the original cause(s) of marsh loss (e.g., altered hydrology, low water clarity, invasive species, erosion from boat wakes, or shading from overhanging tree branches on the bank). Planting of marsh grass to stabilize the shoreline has been used successfully for many years.

Seagrasses

Submerged vegetation such as seagrass stabilizes the sediment and may contribute to wave attenuation at low tide. The value of seagrass beds for shore protection is limited by their seasonality. During the winter months, seagrasses in temperate areas become less dense or may even disappear, providing less protection during the season when increased storm activity may bring increased wave activity. The highest degree of wave attenuation, and hence potential shore protection, occurs when seagrass occupies the full height of the water column.

Replanting of submerged aquatic vegetation (SAV) is typically undertaken to restore habitat after these plants have been lost in the sub-tidal area.

Vegetated Dunes

Dune creation can provide a system to create or maintain a beach because it adds sand that will nourish the area, with or without structural control. Dunes are established along the backshore.

region of nourished beach by planting the appropriate species of dune grasses. Sand fencing, in conjunction with dune grass plantings, helps induce baffling and settlement of wind-blown sands.

Harden

Perhaps the most widely applied shoreline technique is to harden the shore or bluff with some type of fixed structure such as a bulkhead, seawall, or revetment. The primary goal of hardening the shore is to protect the coast from wave attack by creating a barrier to the erosive forces.  Traditional shoreline hardening design involves methods applied at a local or regional scale, often utilizing local materials such as stone, wood, and concrete, and built using techniques familiar to local marine contractors and property.

Seawalls

Seawalls differ from bulkheads in that they are designed to withstand greater wave energy and are more likely to be constructed on open coasts to protect against ocean wave climates. They are most often constructed with castin-place concrete; other materials such as timber are rarely used. These structures can be vertical, curved or stepped to help divert or redirect wave energy. A sloped face may reduce the effect of toe scour but conversion of habitat will still occur if erosive forces continue to remove sand.

Breakwaters

Breakwaters consist of a single structure or a series of units placed offshore of the project site to reduce wave action on the shoreline. The structures are composed of various types of materials but usually employ what is “locally” available. Rock is typically used for construction and has been shown to be very durable when properly designed and installed.

Sills

Sills are generally semicontinuous structures built to reduce wave action and thereby preserve, enhance, or create a marsh grass fringe for shore erosion control. The sill is often built along an existing marsh fringe to maintain its integrity and enhance the protection afforded by the marsh in controlling erosion on the adjacent upland. The addition of sand with marsh grass plantings provides a stable marsh fringe system in low to moderate wave energy environments. Breaks or windows in the sills are recommended to allow the ingress and egress of marine fauna.

Building a sill system requires encroachment bayward or riverward, usually beyond Normal High Water or Mean High Water (MHW), constituting the property limit in most states and complicating the process for obtaining permits for installation. There is often a trade-off of habitats in constructing a sill system. The eroding bank, narrow beach and nearshore are converted to a stable bank, marsh and stone sill. In addition, the sill system may reduce the sediment supply to adjacent shores.

 

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