Last edited 15 Nov 2016

River engineering

Contents

[edit] The importance of rivers in the built environment

Many of the world's greatest cities were founded on the banks of rivers. This was to enable their inhabitants to benefit from the opportunities offered by rivers in terms of food, trade and defence.

As well as providing a secure source of water to drink and irrigate crops, rivers provided early settlements with a ready source of nourishment. According to Natural England, the inhabitants of London consumed over 700 million oysters in 1864.

Before railways, which is when many of the world's cities were founded, boats and ships were the only economic means of transporting goods. Cities required efficient trading links to be able to provide for their inhabitants as well as to prosper. In the UK extensive canal networks were built to connect rivers and facilitate trade. The longest is the Grand Union Canal which links the north of Britain into the Thames and London.

London was first settled as a sheltered inland port with quick access to the open sea. The Thames made the location of strategic defensive value.

Over time, as cities prospered and the use of the railway spread, the population's connections with rivers declined. Rising populations put increasing pressure on land; embankments were built and marshes drained. Rivers were contained, sometimes channelled underground. As more and more riparian land was claimed for development, urban watercourses were systematically polluted by industry. Many brownfield sites show the legacy of these times.

Below: The wetland bowl was an important element of the waterspace masterplan of the Olympic Park developed by Buro Happold. This brownfield development was designed to provide amenity, improve biodiversity and reduce the area's risk of flooding, with 4,000 homes removed from the local flood envelope following the development. (Image copyright LOCOG)

Olympic Park wetland bowl.JPG

[edit] The role of the water engineer

Water engineers are working to reverse these negative trends, reclaiming rivers as focal point of recreation, amenity and environmental value. Water engineers help developments understand the likely behaviour of rivers and help design teams reduce the risk of flooding.

The range of their work is outlined below:

[edit] Riverbank protection

This includes

  • Asset appraisals.
  • Flood defence.
  • Moorings.
  • Access.
  • Outfalls.

Below: Steel sheet piling on the River Avon. In this project, ground anchors were relocated, surface water outfalls upgraded and moorings provided by timber fenders along the river frontage. (Image courtesy Buro Happold.)

Riverbank protection Buro Happold.jpg

Some river edges are undermined by geese eating riparian plants providing banks with their structure while others are at risk because of shipping or lack of maintenance. The scale and nature of an engineer's work depends on the project.

[edit] Environmental and ecological enhancements

This may include working with environmentalists and ecologists, for example in the construction and planting of reedbeds. Reedbeds serve a number of important functions:

  1. They provide habitats and promote biodiversity
  2. They offer opportunities for education.
  3. They act as a water purification measure (at Heathrow Airport reedbeds were included in the scheme to purify water off the runways)
  4. They provide a visual and recreational amenity.
  5. They act to slowing the flow of water. This action needs to be balanced with the water capacity required of the river to ensure its flood risk does not increase. It may be necessary to widen the river at the point at which the reedbed is created to offset its slowing effect.

Below: The wetland bowl was an important element of the waterspace masterplan of the Olympic Park. The site under construction makes it clear how the river wall is stepped down and the surrounding area sculpted out to hold water following a rainfall event further up the catchment of the River Lea.

Wetland Bowl on the Olympic Park during construction.JPG

Below: Once the wetlands had been planted with reedbeds the enhancement for local biodiversity and amenity is clear. Image copyright Alex Harvie.

Reedbeds on the Olympic Park.JPG

[edit] Canals

Below: Sluice gate on a canal.

Canal sluice gate.JPG

Canals are human-made channels that have been used throughout history for water conveyance (supply), or to service water transport vehicles.

Canals use engineered structures such as:

  • Weirs and dams: To raise river water levels to usable depths.
  • Looping descents: To create a longer and gentler channel around a stretch of rapids or falls.
  • Locks: So that ships and barges can ascend and descend.

The two types of canal are waterways and aqueducts. Aqueducts are water supply canals used for transporting potable water for human or agriculture consumption. Waterways are used for carrying vehicles transporting goods and people. They can be connected either:

  • To existing lakes, rivers, other canals or seas and oceans.
  • In a city network: such as the Canal Grande in Venice, the gracht of Amsterdam and the waterways of Bangkok.

Canals can be construction in different ways, such as:

  • A new canal can be created by excavating the body of the canal and providing water from an external source, like streams or reservoirs.
  • Dredging a channel in the bottom of an existing lake which is then drained.
  • A stream can be canalised to make its navigable path more predictable and easier to manoeuvre. This involves dredging, damming and modifying its path.

[edit] Wadi design

Below: Wadi Hanifa Wetlands in Saudi Arabia, (image copyright Arriyadh Development Authority).

This 120km long, 4500m2 watershed passes through the capital city of Riyadh. It has been developed into an environmental, recreational and tourism resource following an extensive development. The focus of the masterplan was to restore the Wadi's natural beauty which had been spoilt by decades of unfettered dumping and development. The Wadi had also suffered from seasonal flooding every 5-10 years and works improved its flood performance booth in terms of flood and dry weather flow performance, channel conveyance and water quality remedidation and scour protection.

Wadi Hanifah Wetlands Buro Happold.jpg

[edit] Level control structures

Level control 3d lock gate Buro Happold.png

Above: A 3D image showing a lock gate with curved doors and a hydraulic control mechanism. Image copyright Buro Happold Water Group.

The work water engineers undertake on level control structures includes:

  • Spillway design.
  • Weirs.
  • Gates.
  • Larger structures like tidal barriers. For example, as part of the development work on the Olympic Park, water engineers designed and installed Three Mills Lock to make the upper part of the Lower Lea Valley non tidal. This was undertaken to enable navigation without the constraint of the tidal window and to improve water quality. By closing off the potential for outfall from The Becton Sewage Treatment Plant at Lea Bridge Sluice, contaminated water could no longer rise up the river on the high tide, depleting oxygen reserves in the water body and killing fish.

[edit] Navigation

This includes:

  • Dredging works.
  • Ship impact protection.
  • Camp-shedding.
  • Jetties.
  • Locks.
  • Canals.
  • Transportation strategies.

[edit] Waterspace masterplans

This includes:

  • Developing strategic masterplans to balance competing needs such as commerce, waterfront, navigation, environment, education, amenity and recreation.

Below: A waterspace masterplan by Buro Happold for Little Belhus.

Waterspace masterplan Buro Happold Little Belhus.jpg

[edit] Stakeholder consultation

The primary individual in a project is the client. However on most construction projects, and particularly on those which involve water, there are a number of stakeholders, consultees and other third party groups. These include:

All these groups have valid and vested interests in river and coastal projects. The biggest cause of problems in the consultation of water engineering projects is late or insufficient communication with stakeholder groups. This may be caused by a lack of understanding on the part of the client team. For example, many clients are not aware that of range of roles undertaken by the Environment Agency. A client may have a positive meeting with one team (eg ecology) without realising they need to hold separate talks with other parts of the organisation (eg flood risk). This almost makes the EA a project in their own right.

It is always better to connect with stakeholders early and to be open about plans so there is time to establish relationships and build mutual trust.

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