This policy statement by the Inland Waterways Association (IWA) covers the standards for construction, restoration and maintenance of inland waterways. It recognises the diversity of the waterways and the importance of their heritage.
It is concerned with all waterways used by commercial craft (of all types and local variations), as well as waterways used primarily for amenity purposes. However, the waterways are a dynamic living system that is continually changing. The needs of modern users are different from those of the past and opportunities continue to arise to enhance the system to meet modern needs.
This policy statement applies to maintenance, repair and enhancement of all existing waterways, whether currently navigable or derelict, as well as to construction of new waterways.
2.1 The Association will oppose all attempts to reduce the craft gauge of a waterway (i.e. the maximum size of vessels able to use it).
2.2 The Association will press navigation authorities to maintain each waterway in a satisfactory condition safely to accommodate vessels of its craft gauge and to permit access by such vessels and to ensure that the navigation channel is not blocked by craft so as to prevent through navigation by vessels of its craft gauge.
2.3 The Association will press for the restoration of dimensions suitable for the passage of vessels of the constructed gauge where subsequent works or deterioration (such as subsidence or structural movement) have created pinch points.
2.4 The Association considers that the opportunity should be taken to make minor improvements to achieve the appropriate constructed gauge where structures of heritage value are repaired or restored.
2.5 Where either temporary or permanent works are planned which will affect a waterway (e.g. road, rail, or utilities crossings; bridge reconstruction; riparian development) the Association will press for retention of dimensions suitable for the passage of vessels of craft gauge. Where such works are planned to cross the route of a proposed new waterway or of an existing waterway proposed for restoration or enlargement, the Association will press for the provision of adequate clearance for vessels of the intended craft gauge so that no new pinch points are created.
The Association has the following views on gauge.
3.1 Any works intended to extend or enhance the waterway network should take into account:
3.2 Works to accommodate craft of dimensions less than the relevant standard craft gauge would comply with Policy 3.1 if the route involved repair (as opposed to rebuilding) of a substantial number of structures (e.g. locks) where these were originally built for craft of less than the relevant standard craft gauge.
3.3.1 For each new narrow or broad waterway, the craft gauge should not be smaller in any dimension than the respective standard craft gauge.
3.3.2 For each narrow or broad waterway which is under restoration or currently navigable:
The Association considers that any study of a project involving construction of a new waterway, enhancement of a waterway or restoration of a derelict waterway should consider:
NOTE: These issues are not listed in order of priority.
The Association will normally:
The Association considers that:
The Association considers that ideally every waterway should have:
In certain circumstances there may be environmental constraints affecting achievement or maintenance of the waterway’s capacity to accommodate vessels of constructed gauge. In these cases the Association prefers environmentally acceptable ways of accommodating vessels of constructed gauge rather than accepting a restriction to vessels of a smaller gauge.
Wherever practicable, heritage structures should be restored with similar materials and building methods as originally constructed, as long as it can meet the current needs for the use of the structure. Lock gates and lock gear should also be restored using designs that were contemporary with the waterway’s construction or were known to have been used at some time during the life of the waterway. However the heritage value and appropriateness of restoring to the original design should be assessed on a case by case basis.
10.1 Overflows take the form of by-washes conducting water supply around locks and side weirs allowing the discharge of excess water to protect navigation works from flooding. Each should be adequate to accommodate reasonably anticipated maximum flows.
10.2 On river navigations, flood locks, flood gates or similar devices are typically needed at the head of each side cut to protect the navigation from flooding.
10.3 The need and adequacy of side weirs should be determined before a pound is first filled on restoration or, if already in water, before being acquired from a third party.
For the purposes of this document, the following definitions will apply.
The constructed gauge varies among waterways and this policy statement seeks to ensure the protection of this gauge as a minimum in each case. Subject to paragraph 3.2, for structures being built new or rebuilt (but not for structures being reconstructed for conservation purposes or being repaired), the standard craft gauges for narrow and broad waterways are:
For modern freight waterways, an internationally agreed classification system is in place (CEMT, 1992). Most principal waterways in western Europe accommodate or are subject to proposals for enlargement to accommodate, vessels of the following craft gauges:
** - for one, two or three layers of containers respectively.
Width and depth - In slack water lengths (e.g. canals and some canalised sections of river navigations), the minimum dimensions of the channel required to accommodate craft of gauge beam B and gauge draught D at normal water level are as follows.
These dimensions will need to be increased in river sections and other sections with significant flow, to allow for the effects of current and changing water levels.
Cross-section - In lengths where the channel is not restricted by structures or other local features, the ratio of the water cross section to the wetted cross section of a craft of craft gauge should be no less than 3.5:1, as an absolute minimum for short lengths, but 6:1 or greater is preferred, to reduce erosion and adverse effects on fringes of vegetation.
Channel lining: - Where new channel lining is installed, the depths and channel cross-section it creates should comply with the above requirements for craft gauge beam and draught.
Tidal and river navigations - On tidal navigations and sections of river navigations not covered in A2 above, including those which may have no constructed gauge, channel maintenance specifications should be derived for each waterway, in consultation with users, so as to facilitate safe and efficient navigation.
Bends - In all cases, fairway width on bends should be increased as necessary to ensure that two vessels of craft gauge can pass safely.
The required headroom should be provided over a width of at least craft gauge beam. For safety reasons the Association considers that there should be at least 0.3 m clearance above the craft air draught.
Towpath headroom - a minimum headroom over the towpath of 2.2 m is desirable under bridges.
Freeboard - minimum channel freeboard at highest design water level should be 0.3 m.
The Association has the following views.
Profile - Whenever dredging is undertaken, it should recover the full constructed channel profile subject to local engineering constraints. Where it is not possible to confirm the dimensions of this profile, it should be estimated as a channel with the dimensions required above to accommodate vessels of constructed gauge or that defined by the original channel lining (e.g. puddled clay), whichever is smaller. Where the channel dimensions have been reduced by subsequent lining (e.g. with concrete or geotextile), dredging should be undertaken to the profile established by that lining in the lined length only.
Triggers - Dredging should be required as soon as the depth in any part of the fairway has degraded to less than the constructed gauge draught at normal water level. Dredging should be required at landings, wharves, and moorings as soon as the depth there has reduced to less than the constructed gauge draught.
Tidal waters - On each tidal navigation, a dredging plan should be agreed in consultation with users.
November 2012 (updated February 2016 and April 2019)