Rainham Silt Lagoons - Water Management IssuesThe Operations Plan takes steps to ensure that water quality and water levels are managed appropriately during (and after) the dredge disposal process. Water Quality
The discharge from the lagoons shall be controlled to ensure that the suspended sediment levels in the water entering the drainage system in the Marshes is in accordance with the criteria set out in the Waste Management License. Maximum Volume per DayThe volume of material that the site can accept is dependent on the grading (size) of the material in suspension. Coarser materials are more likely to cause water level management issues since the volumes of water associated with the pumping operation are greater and the settling time for the material is so short. In consequence, there is a tendency for discharge rates from the sluices to run at the maximum capacity of the marsh drainage system – around 60,000m3 per day. The limit on capacity for placement is set by the capacity of the receiving lagoon structure, since water is retained, rather than discharged. Condition of Ditches and Drainage SystemThe PLA, the Operator and the RSPB will undertake a joint inspection of the ditches adjacent to the lagoons with sufficient notice to allow any remedial works to be undertaken. All ditch management should be undertaken according to best conservation practice, and particular note should be taken of the area’s status as an important site for water voles. Natural England has produced water vole guidance for planners and developers which sets out best practice for water vole habitat management. Ideally ditch management should be undertaken on a rotational basis so as to avoid loss of habitat from a large length of ditch in any one operation. Control of Water Levels During/Post PumpingWhere practicable, sluice gates should remain closed during pumping campaigns. However, there may be a requirement to open the sluice gates when pumping particularly coarse material as this requires large volumes of water to mobilise. If lowering of the sluice gates is required, efforts should be made to lower adjacent gates simultaneously at a consistent level to prevent localised drawdown and the build up of ammonia within the receiving ditches. Sluices should also remain closed post-pumping to prolong water retention and to ensure an even flow of water.
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