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Ground conditions

At the feasibility stage a detailed site investigation is not required unless you are proposing to construct a lay-by marina (see section below).

However, it is advisable to assess the site conditions which will impact on issues such as excavation, disposal of spoil, potential contamination and ultimately determine the method of construction and the major project costs. It is also advisable at this stage to identify whether or not the site has utility equipment or private services crossing it which will impact upon construction and use.

A detailed contour map and site walkover would give an idea of the levels and therefore any need to excavate or raise banks. The cost of disposing of excavated material off site can be significant. It will assist the viability of your scheme if you can dispose of this within the site of the marina or on other land which you may own. This may require planning permission. If this is not an option seek estimates of disposal costs from local landfill operators.

The permeability of the ground is of critical significance to the cost of construction. A geotechnical desk study and ground model at the initial feasibility stage will identify, quantify and determine how to manage the risks associated with the ground. Best practice is to compile a geotechnical risk register, which should include issues related to contamination, disposal, etc.

If the marina basin will hold more than 25,000 cubic metres of water above ground level it may come under the provisions of the Reservoirs Act 1975.

Lay-by marinas

Lay-by marinas on the towpath side of the canal will not be permitted and an entrance (isolation) structure must be provided along with a towpath bridge to accommodate the towpath. Permission is unlikely to be granted for a towpath to be diverted markedly from its original line, such that it cannot be used for its original design function to facilitate the towing of boats.

Lay-by marinas on the offside of the canal will be permitted and must satisfy design criteria for marina entrances to ensure the lay-by footprint extends far enough into adjacent land to accommodate all types of boats and allow sufficient room to manoeuvre boats safely, and without encroaching on the navigation.

Typical Marina/layby marina entrance detail

Where an isolation structure is not used, it is extremely difficult to establish whether the new marina satisfies our requirements for water tightness, as it is not often possible to carry out initial or secondary stilling tests.

  • It will be necessary for the applicant to carry out a more comprehensive and extensive ground investigation to prove the suitability of the ground where a lay-by is planned. Refer to Design - Requirements for site investigation.
  • It will be necessary to excavate trial holes along the full length of the proposed lay-by to prove the ground conditions are suitable for wet working.
  • Site investigation and soils testing will be necessary to prove the soils on site satisfy the requirements of our Puddle Clay Specification.
  • Construction of this type of marina can present a much greater risk of undermining the structural integrity of the canal bank and lining.
  • Further investigation/analysis may be required to satisfy our concerns where the proposed works may undermine the integrity of the canal.

British Geological Survey

British Dam Society

Last Edited: 16 February 2022

photo of a location on the canals
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