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Water levels, flood risk, discharges and water quality

Although typically much less variable than river navigations, which can have very considerable level changes over short periods, canal water levels can still vary, sometimes quite rapidly.

The range of level variation will be dependent on a number of factors, such as length of pound, proximity to controlled and uncontrolled inflows, amount that upstream and downstream locks are being used, navigable depth in relation to pound datum, and canal freeboard, to name a few.

Most canal water levels are managed around a normal operating zone (NOZ) which is typically +/- 200mm, but water levels outside of the NOZ may be experienced at times. The design of your marina will need to take account of reasonably foreseeable water level variations to ensure safe access to and egress from moored boats.

Solutions include floating, rather than fixed, pontoons. Please seek advice from the relevant New Marinas Technical Manager for specific information on the likely range of water level variation at your proposed marina location, whether on a canal or river navigation, to assist appropriate design.

The Environment Agency can advise on whether your site is in one of these locations. Any development in flood plains will need Environment Agency consent.

Flood risk

There are two main impacts of a mooring development on flood risk.

The first impact is the increased risk to the waterway from the development associated with the mooring site. For example, the construction of hard standings, new buildings and infrastructure may increase the rate of run-off to the waterway. Refer to our guidance below on accepting surface water discharges.

The second impact is the risk to the mooring site and its infrastructure from the waterway. A Flood Risk Assessment (FRA) is required with your planning application and it should be consistent with this guidance. It is important that you include us early in the scoping of the FRA.

Basins or marinas retaining more than 25,000m3 of water above natural ground level are likely to come under the provisions of the Reservoirs Act 1975. The approximate dimensions of a marina of this magnitude are 15,000m2 in area and 1.5m deep which would accommodate approximately 150 boats. The marina will require specialist input from Reservoir Panel Engineers and a rigorous maintenance and inspection regime under the auspices of the Environment Agency.

Surface water discharges

We generally don't encourage discharges of surface water from rainfall events to the proposed marina basin or adjacent canal. This is because these flows occur when the canal system is already dealing with high flows. However, if you wish to make a proposal to discharge surface water from your site, either into the proposed basin or into our waterway, it will require our consent.

Any discharges, including surface water drainage of impermeable surfaces, will only be agreed to if there is no increase in the flood risk and they will not cause the water quality of the waterway to deteriorate, either in the long term, or as a result of increased discharges. We will only accept clean surface water. We will not accept foul, polluted or contaminated water. Discharges of trade or sewage effluent are not normally accepted on water quality grounds due to the relatively static nature of our waters.

To allow us to consider your proposal, you will need to provide detailed information including calculations showing the relevant catchment areas, run off quantities, outfall size(s) and location(s), and the sizing of oil and silt traps that will be required. We will advise you what detailed information we will need and the extent of any modelling/assessment we will expect you to undertake.

If consent is granted we expect you to use best available technology to treat and regulate any discharge. We may require oil interceptors and silt traps to be fitted. We support and encourage sustainable methods such as reed beds filtration. We may also require mitigation against any increased flood risk, for example additional weir capacity or works to another structure, which would be funded by the marina developer.

In addition you will require a separate licence with us which includes standard clauses to ensure that issues of water quantity and quality as well as any construction issues are properly addressed. There is no charge for surface water discharges made from property and structures directly connected to the provision of mooring. Payment is however likely to be required in respect of discharges for all other purposes. Refer to the Our Application Process - Legal Agreements page for more information on the Surface Water Discharge Licence.

Surface water discharges may also require consent from the Environment Agency. This includes roof and car parking drainage and will depend on the size of the area drained and the risk to the waterway. Drainage from areas with commercial activities, e.g. working boatyards, can be subject to Trade Effluent Agreements with the Environment Agency. They also issue Pollution Prevention Guidance.

CIRIA (The Construction Industry Research and Information Association) have information and good practice relating to sustainable drainage in the built environment.

Storage of fuel and other substances

Diesel tanks, hazardous substances and other commodities will need to be stored in bunded areas that are capable of holding at least 110% of the volume of material stored. Storage tanks and dispensing equipment will need to be installed in accordance with current legislation and should be located so that the use avoids spillages into the mooring area and subsequently entering our waterway.

Oil emergency facilities should be kept on site including spillage clean up and, if appropriate, the means to isolate the marina described in Design-Construction Performance Criteria. Measures may include oil absorbent materials being available and attention to any refuelling facilities that might be provided at the marina. Fuel storage facilities may require a fire officer's approval which may influence their siting. An emergency plan for dealing with a pollution incident should be written in line with Environment Agency guidance.

Discharges from boats

Sewage from boats must not be discharged into the water. Facilities such as pump-outs and Elsan disposal units should be provided on site for the emptying of boat holding tanks. The location of these facilities must be carefully planned to minimise effects from spillage. Residential boats can be directly hooked up to mains sewage disposal via their service bollard when they are at their mooring. This can remove both sewage and grey water (see below) for this 'high use' group of customers. Because this facility avoids the customer handling any waste, it is greatly valued by them.

Consideration should be given to 'grey water' from boats, which includes waste water from sinks, showers and washing machines. We encourage recycling processes and collection of waste water to prevent overboard discharge into the mooring site.

Whilst clean rain water may be pumped from bilges, engine compartments must not be emptied into the water.

Water quality and stagnation

Basins, marinas or areas within them may become stagnant when there is little boat movement. This in turn can lead to formation of scums, possibly blue-green algae blooms and gassing sediments. Formal monitoring is not usually necessary but problems will become self-evident. Failure to address this issue at the design stage may lead to customer complaints as the perception of poor water quality is heavily influenced by surface water appearance.

Good design and management can overcome this by ensuring regular boat movement across all areas. Otherwise, aeration and circulation technology may be required. There are a number of low-cost solutions available based on solar and wind power that simply ensure that water is kept moving. A 'sweetening flow' could be considered using a by-pass pipe, although this must be capable of being closed off when required.

Environment Agency
Government planning portal
CIRIA (The Construction Industry Research and Information Association)

Last Edited: 13 May 2024

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