River control structures

River structures should serve more than engineering objectives.

Structures are used to control the flow of rivers for a number of purposes, including bank stabilisation, water storage, flood protection, depth regulation, aeration, flow measurement, and storm detention. They also affect fisheries, wildlife, swimming, boating, and the visual appearance of our towns and countryside. Structures can be designed with either single or multiple objectives in view. It is only in exceptional circumstances that multiï¾­objective designs have been attempted [Fig 9.20]. The best examples are in semiï¾­arid countries where water is scarce and highly valued for economic, aesthetic and religious purposes. The stepped tank wells of India were conceived as multiï¾­purpose projects and admired by Patrick Geddes. He tried to halt the European practice of filling-in the tanks to control Malaria. Geddes pointed out that tanks cool the air, help to control flooding and can be stocked with fish (Geddes 1917). In Iran there is a long history of designing structures which serve as dams, weirs, bridges and pavilions. The most famous surviving example is the Khaju Bridge outside Isfahan [Fig 9.21], which carries traffic and feeds irrigation canals. Its superstructure was part of the original design, unlike the adventitious buildings on Old London Bridge and the Ponte Vecchio: From the steps on the lower side of the bridge the people wash their linen or play in the cool water, and interior stairways lead thence up to the second story of the bridge... Poets in contemplation, mullahs and philosophers in argument, families in reunion, gossiping women and friends at various amusements, all may enjoy the beauties of the scene in isolation and comfort (Pope 1939: 1237). 9.21 Kahju Bridge, in Iran, could be the best multi-purpose water-retaining structures which has ever been made Britain also has examples of river control structures which are 'more than engineering'. They occur either in important cityï¾­centre locations or as the product of an enlightened attitude to the landscape of industry. In London, the Victoria Embankment is a historic example of a multiï¾­purpose project, though it spoiled the riverbank. Joseph Paxton was instrumental in its promotion. The embankment serves for river protection, as a promenade, and as the route for an underground railway and a trunk sewer (Chadwick 1961: 216). There are handsome sections of river embankment at Greenwich, Hammersmith and Strandï¾­onï¾­theï¾­Green, but many opportunities were squandered during the period 1972ï¾­84. When construction work began on the Woolwich Flood Barrier in 1972 it became necessary to launch a massive programme of downstream flood protection works, largely funded by MAFF. The opportunity for creative riverside design was taken up in some places. MAFF partï¾­funded the architectural design of the Barrier and the GLC laid out viewing gardens on the adjoining banks. Elsewhere the flood walls and embankments were built in a crude and unsightly manner [Fig 9.22]. Even at Thamesmead, the site of a major GLC housing project, the flood wall was designed by engineers and then 'decorated' by landscape architects. The Otterspool Promenade, designed as part of the 1984 Liverpool Garden Festival, is a very much better example of joint design by landscape and engineering specialists (Turner & Lancaster 1984). Similarly, the Rhine embankment in Cologne is both a flood protection measure and a fine park. Other British cities have also considered the amenity aspects of river engineering. In Bath: Alternative forms of sluice were suggested, one being a radial gate and two vertical lifting gates. These were submitted to the Royal Fine Arts Commission who recommended the radial gate in principle, but requested that the services of a landscape architect be obtained to produce the most aesthetically pleasing overall scheme. Mr Conder, of Casson, Conder and Partners, was appointed and he has produced a scheme which does not derogate from the hydraulic requirements, is aesthetically pleasing and fits in with future proposals of Bath Corporation in the area (Greenhalgh 1968). The Pulteney Weir is beautiful [Fig 9.23]. Equal care should be given to other structures, even when they are not in the midst of historic cities. Weirs and sluices can also be designed for active recreation. Canoeists are often seen paddling into the 'white water' generated by river control structures. In 1972 a group of Bedfordshire canoeists asked the Anglian Water Authority to find a site for a canoe slalom course in a very flat part of England (Anglian Water Authority, 1982). The Authority took up the idea and in 1981ï¾­2 built a slalom course at Cardington Lock 2.5 km east of Bedford. The course has a dual function, acting primarily as a river flood control structure and at other times as a canoe slalom course. There is a control sluice at the head of a concrete lined channel which connects the upper reach of the river to the lower. Immediately downstream of the control sluice is the canoeists launching pool, leading directly to the slalom channel. The cost of the structure was ,273,000 of which 50% came from the Great Ouse Local Land Drainage Account (with grant aid from MAFF), 24.5% from the Anglian Water Authority's Recreation and Navigation Account, 18.3 % from the Sports Council and 7.2% from a group of 8 local councils. From a landscape planning viewpoint the Cardington slalom is a notable achievement, and superior to any river control structure in the Lea Valley Regional Park. But as a landscape design it is only a moderate success. The Teesside Whitewater Course on the River Tees, near Stockton, also succeeds as a landscape design [Fig 9.24]. It was made possible by Teesside Development Corporation's construction of the Tees River Barrage. The whitewater course is on land previously operated as a tip for construction industry material. It was shaped to form a bowl. The scheme incorporates a navigation lock, a fish pass, a warm-up lake, a caravan and camping park. It also makes an addition to the local network of wildlife corridors. It is an admirable example of a multi-purpose river control structure (Davis, 1995).