Our criteria in the design of a mooring basin or marina include:
- water tightness
- the ability to isolate the marina from the main waterway
- integrity and durability of construction including any lining system
- the safe access and egress from the marina (marina entrance design/layout)
- environmental impacts and considerations
- accommodating the towpath, any necessary bridges and service diversions (if the site requires access from the towpath side)
- drainage of water from the development
The site assessment and design needs a structured approach, including a formal geotechnical desk study (with associated report), followed by detailed investigation, and an engineering design stage. Normally, the desk study is required at site evaluation/feasibility stage, followed by detailed investigation and design.
Constructing the edges of the void
The principal functions of the basin edges/bank protection include:
- water retention
- prevention of erosion
- carrying loads
- providing the connection to pontoons
Design of retaining structures is complex, requires an understanding of the ground conditions, structural loads and proposed use, and should only be undertaken by suitably qualified specialists. Many forms of edge creation and bank protection are available. Piling is the most common form but concrete and masonry walls are also a possibility.
A structural system of bank protection, such as interlocking sheet steel piling, is likely to be needed for areas where the retained height is significant, or there will be surcharge loads from other sources such as craneage, car parking, vehicle deliveries, tankers, etc. The design must be appropriate for the foreseeable end-use of the structure.
It is usual to install a reinforced concrete capping beam to structural piles to prevent damage to boats. Galvanised trench sheets are non-structural but are sometimes used where craft must lie alongside the bank. Capping beams should ideally be made to accord visually with vernacular building materials, for instance by laying brick or stone masonry to the upper face and fendering the vertical face.
The method of future maintenance of bank protection systems should also be considered at the design stage.
Soft edge details can look more pleasing in many settings, offer an opportunity for wildlife and can be significantly cheaper than hard bank protection. If they are to provide access to boats, the soft banks will require a 'bridge' detail between the edge and pontoons as there is usually insufficient depth to moor within about 3m of the soft edge because it slopes. Services will also need to be located within any bridging structure.
Fixing the pontoons in place
The solution depends on the site conditions, form of construction and whether water levels fluctuate.
If the bed is natural clay, the pontoons may be located by piles driven into the bed. A lined marina presents more difficulty. Puddle clay may need to be re-puddled around piles. Modern liners have specific solutions such as gaiters.
Pontoons can be fixed or static (supported off the bed or alternatively floating, tethered at suitable locations). Most floating pontoons are supplied on a design and build basis and manufacturers will normally produce a layout as part of their quotation for supply and installation. It is advisable to use a good quality pontoon and fittings, such as cleats, service bollards and fenders. These are likely to be the safest, easiest to maintain, have the longest life, meet customer demands and ensure a standard of quality.
Pontoons and the access to them will need specialist design in fluctuating water levels. Canal water levels vary little and no particular precautions are necessary. Some canals that are constructed near rivers are subject to occasional inundation with rising levels. River levels fluctuate with rainfall and drought. Lock cuts (artificial canal sections on river navigations) are also affected.
Moorings or marinas on river navigations will need to have mooring pontoons capable of operating in a range of water levels with flexible connections to dry land. Floating pontoons accessed by link bridges are normally used. They rise and fall with river levels, removing the need to adjust mooring ropes. There may be some restrictions imposed on boat movement during flood conditions or exceptionally low water levels.
Tidal rivers and waters fluctuate daily and represent a further dimension which may require special consideration in terms of 'rise and fall' access. Boat movement may be restricted at low water levels. Moored vessels may need to 'bottom out' and rest on the river bed at low tide. This may require the creation of flat beds on which they can rest. To maintain a marina in water at all states of the tide, an entrance lock or tide gates may be needed.
Refer to the Design - Water levels, flood risk, discharges page for more information on water levels and flood risk.
Locating the entrance of the mooring basin/marina
The entrance to a basin/marina should be located and designed to minimise the effect on other canal users. Existing structures such as bridges, locks, weirs, sluices, feeders, existing moorings and established reed beds can affect the ability of crafts to manoeuvre safely when accessing/egressing a marina.
Sight lines should also be considered when locating a marina entrance. As a general rule, oncoming boats approaching the entrance should have a minimum line of sight of 40m in each direction from the centre line of the marina entrance. Given this, the marina entrance should not be located within the vicinity of a bridge, lock, weir or other asset or control structure.
(Note: The above entrance layouts are best practice guides only and have been designed to accommodate boat lengths of less than 20m. If you are designing an entrance to accommodate boat lengths of 20m or greater, please contact us to discuss the specific requirements.)
The entrance to the basin should generally be no wider than the standard lock gauge of the navigation unless the manoeuvring of boats requires it.
Please note that our waterway dimensions should act as a guide to where larger craft are limited to navigate safely and as such 'narrow' canals generally cannot accomodate 'wide' craft.
Signage requirements to warn approaching boaters may be required (at your expense). Passing boats may use the entrance to turn around and this should be considered in its design and siting. Your design should consider attributes of the site, prevailing wind, waterway constraints and level of traffic.
The basin should be separated from the main navigation by an undisturbed berm that is lined and armoured as appropriate, so that the entrance cannot be by-passed by water.
Hard bank protection around the entrance to the basin/marina will be required (at your expense) in order to prevent erosion and scour. Similar protection may also be required to the bank opposite to the marina entrance.
You will also need to consider any dredging requirements in the waterway around the entrance. In some cases works may be required to widen the waterway locally, for example to create better turning circles or a lay-by to accommodate a full length boat accessing the basin/marina safely. These areas will need to be constructed to full depth, typically 1.5m. Soft bank protection may be required within the vicinity of the site to reduce erosion from increased boat movement. We may not own the bank and in these circumstances permission to install the protection measures will need to be obtained from the relevant land owner.
Towpath bank protection
Craft accessing and egressing the newly created marina basin will create a wash which will impact the towpath bank. A minimum of 30m of bank protection will be required either side of the marina entrance central line (as demonstrated on 'Typical Marina Entrance Detail diagram). This detail should be included within the DCA submission and the works carried out at the same time as the entrance works.
We will require a bridge over the marina entrance to ensure continuity of the towpath for existing uses which may, in addition to pedestrian use, include towpath maintenance vehicles, other plant and vehicles, existing utilities equipment, and other services. The bridge should also comply with the requirements of the Disability Discrimination Act and as such be designed to allow its use by all sectors of the communities including people with disabilities.
In some locations the towpath is also a public footpath and the consent of the Local Authority will be required for either temporary or permanent diversions or closures. The Local Authority keeps maps confirming the routes of public footpaths and it is recommended that these are checked at this stage in the process to establish whether your scheme needs to take account of this.
We will check our records for the existence of private rights to use the towpath for services or access and include details in our report to you. The information we provide should not be considered as definitive and you should always check with the Local Authority.
Where the marina is on the offside of the canal there may still be a need for a bridge over the entrance where public or private rights are present. You should consult with the Local Authority on the requirements for any bridge in these circumstances. The Disability Discrimination Act will also apply in this case as it will be used by members of the public.
We will advise on the following:
- headroom required over navigation
- width required
- maximum gross vehicle weight capacity required
- horse-drawn boat requirements
Headroom will normally be defined relative to an overflow weir level.
In mining subsidence areas, a means of maintaining headroom, such as jacking plinths, may be required.
Headroom clearances relating to arched bridges need careful consideration. A profile which will achieve the desired visual and clearance objectives is needed. It is usual to use parabolic arches, with raised and set back spring points to achieve the optimum result.
The impact of the bridge on the canal environment will require detailed consultation. Not only are bridge aesthetics of great importance but also the setting of the bridge on the local and wider landscape must be considered.
Aspects which will be discussed with regard to bridge aesthetics include:
- expression of function e.g. a beam bridge should not have false arch facades
- scale, proportions and mass
- order - avoid chaos
- materials and facings
- architectural features
- parapet type
- parapet/approach safety fence interface
- towpath lighting where appropriate
- access ramps, steps, barriers, gates, stiles, etc
Please note, we will require you to complete a separate Bridge Agreement which will set down ownership details and responsibilities for maintenance. This will include the granting of an easement to us where the bridge is constructed on your land. The bridge ownership and maintenance responsibilities will normally rest with the marina owner.
Making the void water-tight
We need the void that you create to be water-tight in order to retain the water within our network. Essentially we require that water losses from the marina/ basin are below a specified rate of 5mm in depth over the surface area a day. Clearly the design solution will depend on the ground conditions at your site.
Water-tightness may be achieved in highly permeable soils provided the water level is proven to be below the local ground water table throughout the year. This can be hard to demonstrate, but may be realistic, for example in a marina excavated alongside a river navigation, or close to another watercourse which will dominate the water table.
A ground model is required (this should have been produced during the desk study), which considers the natural materials present, their permeability characteristics, and also the pre- and post-development hydro-geological (ground water) regimes present. This should then be used to predict water losses. In addition it is likely that Environment Agency consent will be required for any works affecting the characteristics of underground bodies of water.
The soil characteristics will determine the need for, and type of, lining. If the basin is in impermeable ground, lining will not be needed. Sometimes the bed is in watertight ground and only the sides need to be made watertight.
The choice of lining system is determined by a very wide range of technical issues and specialist advice is essential. Examples include Puddle Clay Specification and modern materials such as reinforced concrete, butyl and geotextile/bentonite membranes which may be only suitable in certain conditions.
Any clay-based membrane shall be a flexible, high density natural bentonite membrane comprising a central core laminated between an upper and lower layer geotextile. The membrane should have proven performance and resistance to the ground conditions to be encountered, including saline conditions and should have a proven permeability of 1 x 10-9 m/sec or less. The system should provide waterproof joints at overlaps and any structures to which it is applied.
Uplift should be considered for lined basins in areas of high or fluctuating groundwater level. You must also take account of the durability of a liner since boat manoeuvring can cause scour, and boat propellers, boat shafts and dredgers can cause damage. Jointing details are a challenge and careful detailing of pontoon support systems need to be undertaken so as not to compromise the chosen lining system. If the adjacent or underlying land is contaminated, the seal must also prevent contamination entering the waterway.
Connecting to our waterway and maintaining its structural integrity
Preserving the integrity of the waterway as well as any mooring/marina construction is of fundamental importance to us. As described above, the proposed construction must be structurally sound and capable of being maintained in a watertight condition.
The site should ideally be at the waterway level, thus avoiding the need for a lock to access the waterway for cruising.
Our waterway network has a great range of channel geometry and detail, including various bank protection systems and linings. This will influence the design and method for connecting your site to our network. You will need to 'tie in' to the deep channel section of the waterway. The design of this junction with the main canal bed must be profiled to provide sufficient depth for navigation and continuity of the lining. Refer to this diagram of a typical canal section with sloping sides, which deminstrates the issue. The method of connection will depend on local conditions.
It may not be achieved by dredging because of disruption to the lining of the canal and the inability to achieve a satisfactory interface under water. It may be possible to connect without draining the canal in certain conditions but a cofferdam or even a stoppage may be needed to temporarily drain the canal of water (which must be done during our stoppage programme). Refer to the Construction- Timing and canal closures page for more information.
Isolating the site from our waterway
We require a basin or marina to be capable of isolation from the waterway so that both you and we can protect our respective water-spaces. (We accept that this is not practical on lay-by mooring schemes.) We will conduct a risk assessment, in consultation with you, to determine the range of options for isolating your waterspace.
This will enable you to protect your basin/marina and the boats moored within it in events such as a pollution or low flow on the waterway (e.g. a breach, drought, or planned stoppage requiring de-watering). This will allow you to de-water the basin for dredging or other forms of maintenance. We also require the marina to be isolated from the waterway network in order to conduct the stilling test (see below) and to protect our network in the event of a leakage from your site or other potential impact extending through to our system, such as pollution.
A suitable structure must be built at the basin/marina entrance to form an impermeable seal when connecting to the channel and allow isolation. This can be undertaken using a variety of methods such as piled cofferdams, flexi dams or the usual option of stop logs. Cut off piling may be needed beneath and around the structure. The requirements of any cofferdam are that it will be structurally secure, watertight and able to be inspected by a competent person who will sign the cofferdam register.
All structures must be protected where necessary by fendering designed and installed to resist the impact of moving craft, vertical movements of water level due to flooding or tides, and to protect the hulls and superstructures of craft from damage.
Refer to the diagram which demonstrates a typical timber stop plank structure (for guidance purposes only).
Filling of the basin and stilling test
On completion of the basin, but before connection to the navigation, a stilling test will be required to test its water-tightness. Please note that filling the basin will require a significant volume of water. Dependent on a number of factors (including the site’s location, time of year, weather conditions over the previous months, number of boats, boat movements, proximity to locks, etc) the filling of the basin may need to be undertaken over an extended period or even delayed. Your programme should reflect this risk.
Please note, water supply will be dependent on the availability and supply. You will be required to supply a programme of works together with target dates and rate of fill to officially request water. We will then assess your request based on current water availability. Please note water will not necessarily be available to fill the basin during the period requested. We will endeavour to update you on the situation during the construction phase.
Where contamination is considered to be a risk, the stilling test should be used as an opportunity to test for leaching into the basin. Refer to the bottom of the page for further information.
The stilling test
We will need to test your mooring site for potential loss of water which will be drawn from our network.
The test involves isolating the basin from the waterway by a double cofferdam, pumping out the space between the cofferdams, filling the basin with water and maintaining this over a minimum period of 14 days to monitor the loss of water level for all reasons including evaporation. If this is found to be within reasonable limits, of less than 5mm in depth over the surface area per day, we will permit the basin to be connected to the waterway.
Whilst we will need to approve the removal of water from our waterway for this test, there is currently no need to apply for an abstraction license to use water from our network for this first filling of the marina.
Please note that filling the basin will require a significant volume of water. Dependent on a number of factors (including the site’s location, time of year, weather conditions over the previous months, number of boats, boat movement, proximity to locks, etc) the filling of the basin may need to be undertaken over an extended period or even delayed. Your programme should reflect this risk. We will endeavour to update you on the situation during the construction phase.
Useful references and links
Last date edited: 24 February 2022