Sep 24, 2015 - The imported material is being trucked along Westover Road to the ... resulting in material becoming sort
Milford-on-Sea Recharge, September 2015
(Updated 24/09/15)
A beach re-nourishment operation commenced at Milford-on-Sea on Tuesday 22nd September. This operation involves bringing in mixed shingle material by road from a local quarry and is similar to previous operations undertaken at this site. The imported material is being trucked along Westover Road to the car park on Hurst Road and tipped directly onto the beach in the corner of the car park (see below). The material is then being spread out along the beach to fill up the groyne bays above the level of mean high water (MHW).
The beach will then be graded using an excavator. It is planned that the work will be completed in about 1 week, subject to suitable tides and weather. Due to continued coastal erosion, the beach at Milford-on-Sea requires regular top-ups of shingle material. These works are typically undertaken in spring or autumn. Typically 3,000
to 4,000T of material are added each year. The imported material is placed to the west of the frontage and under coastal processes it is gradually transported in an easterly direction resulting in material becoming sorted and spread out along the frontage. The site at Milford-on-Sea is very exposed to high energy storm waves. Naturally, the beach would roll back landwards during storm events; however, the seawall is a fixed line and prevents this from happening. Therefore, if the beach is inadequate then the seawall is at risk of significant damage or failure. By maintaining the beach, the risk of damage occurring is reduced. The composition of the beach is important in relation to how the beach responds to wave conditions. In order to add material similar in composition to the existing beach, gravel and sand has been sourced from a local quarry. It is therefore very representative of the material which would naturally erode from the cliff at this location if it were not defended by the seawall. Visually, the appearance of the imported material will change over time. A comparison of how it will look after being worked by coastal processes is demonstrated in the following 3 illustrations: 1. Until the beach sorts and washes the material it will be an orangey-brown colour due to the oxidised sand component.
Imported material
* This is a sample of the imported material that the beach is being recharged with and is typical of the plateau gravel beds that comprises the top few metres of the cliff around Christchurch Bay.
2. During the winter months the beach will become worked by the sea and the fines will wash off resulting in the material reverting back to the colour you would normally expect to see.
Imported material (following washing)
* This is a sample of imported material that has been washed and visually demonstrates the range of material sizes through different grades of sand up to course gravel.
3. The existing beach (shown here) is a mixture of sizes (from fine sand to course gravel). The imported material will be naturally sorted and become mixed with the existing material. It is hoped that this will improve the stability of the beach.
Existing beach material
* This is a sample taken from the existing beach that shows the wide distribution of material sizes. This is visually very similar to the imported material.
Once the imported material is in place, the sea will gradually work the beach and this will release some fine sand which will colour the water. This is likely to occur at an increased rate during the works period and then follow at a more gradual rate, possibly increasing during storm conditions. It is anticipated that at the end of the winter period coastal processes would have had time to wash and sort the material. In addition, because there are fines in the mixture the beach may become compacted and lead to ‘cliffing’ to occur. This is when the sea carves a vertical cliff into the beach. Again, this will naturally disappear with wave action and if it persists into next spring then this will be re-profiled using a small excavator. Other than being better material for the beach, by using local, unwashed gravel it is considerably cheaper than having to be previously processed and mechanically washed. Therefore, more material can be brought in for the same cost and the material can be left to be naturally washed and sorted. Once all the material has been placed, a team of surveyors from the Channel Coastal Observatory will carry out a ‘post works’ survey of the beach in order to assess the changes over the winter.
