LAND DRAINAGE – Talk by K.H. Lambert, Member. At the Durrington Community Centre, 11th December, 1991.
Land Drainage in its legal sense covers all types of drainage from Hill Gripping in mountain areas to the sea defence of lowlying lands, and includes the control of soil water. The subject is a very wide one and the talk was divided into 4 parts i.e.
1. The legal and organisational background.
2. Arterial Drainage.
3. Field Drainage.
4. Sea Defence.
These parts were illustrated by examples from South East England.
1. The Ministry of Agriculture, Fisheries and Food is the Department of Government which is responsible for the Administration of and financial support to Land Drainage and co-ordinates the work of public authorities involved. It provides finance by means of Grant Aid, e.g. 75% to G.L.C. for Thames Barrier.
The talk described the responsibilities of Internal Drainage Boards and traced how rain arterial drainage was catered for by successive authorities from Catchment Boards in 1930 to National River Authority at the present time. Local authorities have also powers to carry out drainage works under grant aid, e.g. the former Greater London Council and Surrey County Council.
2. Arterial Drainage was illustrated by two large schemes i.e. the Rother in Kent and Sussex and the Ravensbourne in South East London. The Rother was a scheme which catered for agricultural land at a very low level and the difficulties in arriving at a truly suitable scheme were described. The solution involved the construction of 23 pumping stations as well as extensive channel improvement and river embankment.
The Ravensbourne scheme was of a completely different character, being in an entirely urban and heavily built up area. The flows to be catered for were very much greater on an area basis since rainfall entered watercourses very much more quickly and concrete lined channels were largely used, together with extensive culverting.
3. Field Drainage had been carried out extensively in England and Wales during the 19th century when 12 million acres were drained, largely due to the efforts of Bailey Denton, a prominent Civil Engineer. During agricultural depressions much work had fallen into disrepair but the food store during the 1939-45 war had necessitated a survival which had continued until the early 1980‘s. For example during the year 1970-71 over 200,000 acres had been underdrained.
Slides and Drawings were shown of field drainage problems and their solutions together with slides of drainage machinery and materials including Plastics.
The importance and scale of this work has now greatly lessoned due to the agricultural surpluses resulting from the Common Agricultural Policy of the E.E.C.
4. The arterial drainage authorities are responsible for the sea defence of lowlying land and during the war and immediate post-war years insufficient attention had been paid to this. In many areas Development had taken place without adequate protection. The disastrous North Sea floods of 1953 altered the situation completely and revised all concepts of standards. In Kent 400 breaches of sea walls had occurred resulting in the flooding of 50,000 acres and extensive damage to industry, e.g. at Erith, Littlebrook, Isle of Grain, Sheppey, together with demolition of the railway line behind the North Sea Wall from Reculver to Birchington.
The types of wall built after these floods were illustrated and described.
Future,sea defence measures were touched upon, in particular the extension of beach feeding to reduce depth of water in front of sea walls.. This practice had first been used in this country on the Wall and foreshore east of Rye’ and involved the deposition of large volumes of shingle.
The effect of Global Warming has not yet been fully determined but at present time an allowance of a rise of 6 mm per year during the projected lifetime of the defence is being made. This may be varied in the light of events and research.
M.A.F.F. is now responsible for an oversight of all sea defence works, both those by N.R.A. and by local authorities.
Following the talk various questions’ were raised and discussed. In particular Mr. E. Jones described the damage to Ridham Dock near Sittingbourne in Kent and remedial measures taken. Similar damage had occurred elsewhere.