DRAINAGE, ARTERIAL. Rivers form, in every country, the natural system of arterial drainage, but it is of ten necessary to supplement them by artificial means to prevent land in the low-lying districts from becoming water-logged. In some coun tries, notably Holland, large areas lie near to, and in some cases below, the sea-level so that a complete system of arterial drainage, depending for its efficiency on continuous pumping operations, is essential to enable the land to be cultivated or, indeed, to be inhabited.
In England a large part of the country was originally marsh land which was gradually reclaimed and brought into agricultural use. It could only be prevented from reverting to its primitive state by a permanent system of drainage, combined, on the coast, with embankments against the inroads of the sea. Where, as in mediaeval times, vast territories were controlled by individual landowners, the responsibility for executing such work fell upon them, as the improvement would accrue solely to their benefit. But where interests were divided, disputes as to liability would naturally arise. In this way, it may be surmised, the need for the establishment of authorities armed with legal powers arose.
The earliest drainage authority of which there is record was set up in the reign of Henry III., with jurisdiction over Romney marsh, but the first public statute dealing generally with arterial drainage was the Bill of Sewers passed in 1531, "sewer" then meaning only a canal or water-course. That statute, on which all later legislation on the subject was founded, provided for the appointment of commissioners of sewers with extensive powers for the prevention of floods and the improvement of rivers. The Land Drainage Act, 1861, defined more clearly the powers and duties of commissions of sewers (i.e., drainage), and also pro vided, for the first time, for elective drainage boards having all the powers of the old commissioners (who were appointed by the Crown) but were elected by the ratepayers of the area over which they had jurisdiction. Such a board could be established for any "bog, moor or other area of land that requires a combined sys tem of drainage, warping or irrigation," on the petition of the proprietors of not less than one-tenth of the area concerned, provided that the owners of two-thirds of the area were in favour of it. The provisions of this act were extended and amended by legislation in 1918 and 1926, which gave certain powers to the ministry of agriculture and to county councils and county boroughs.
In 1927 there were 361 drainage authorities of various types in England and Wales, viz., 49 commissions of sewers, 198 drain age authorities under special acts and 114 elective drainage boards. In addition, county and county borough councils have certain powers under the Land Drainage Act, 1926, and the county councils of Middlesex, Lancashire, Yorkshire (West Riding) and Surrey have powers under private acts.
The multiplication by the spasmodic legislation of 50o years of authorities having varied powers and functions and exercising jurisdiction over areas of all sorts and sizes has resulted in an imperfect system of arterial drainage, while it is estimated that the productive value of 4,362,00o acres of agricultural land in England and Wales depends on its efficiency. Of this area one third is not included in the district of any drainage authority, and it is stated that over 1+ million acres are in immediate need of considered and more or less extensive systems of arterial drainage.
The lack of a comprehensive and effective system for Great Britain is largely attributable to the fact that principles of legis lation and administration which were applicable to the conditions existing when they were first laid down are not applicable to modern conditions. In the first instance the liability to take action to prevent the flooding and waterlogging of land was regarded as falling on the owners of the land, and it was granted that any depreciation in value was the natural result of its situation, and a normal incident of its tenure for which no other person was responsible or by which they were affected. But as time went on new conditions arose ; improvements in agriculture led to the extensive adoption of land drainage on farms (see DRAINAGE, LAND) which had the effect of sending water from the uplands into the valleys much more rapidly and effectively and so con tributing to the flooding of the lower levels, and, in addition, the growth of towns along the rivers, and particularly at their outfall to the sea, tended to obstruct the escape of flood-water. By their systems of water-supply—in some cases drawn from far-distant sources—and of sewerage, the towns also increase the difficulty and complicate the problem confronting authorities re sponsible for arterial drainage ; whence it appears evident that the old principle of charging the whole cost of arterial drainage on the land directly affected—in practice on that lying at ap proximately the level of the highest recorded flood—has become inequitable.
In 1927 a royal commission was appointed to consider and report whether "any amendment of the law is needed to secure an efficient system of arterial drainage without any undue burdens being placed on any particular section of the community." They recommended the repeal of all existing public acts relating to arterial drainage and the enactment of a single comprehensive statute. They suggested that where drainage problems exist the country should be divided into "catchment areas." Catchment Areas.—This term denotes "the whole of the land which directs the drainage towards one river" discharging into the sea, though a tributary stream, especially when it joins the main river near the estuary, may be of sufficient magnitude and importance as to constitute a separate one. It was proposed to constitute 1oI catchment areas with a responsible authority for each, such authority to consist of representatives of the county councils, and county boroughs lying wholly or partly within the area and of other persons elected by any drainage authorities within the area, or, if none exist, of persons directly interested in the drainage of the lowlands. The complexity of the problem is fairly indicated by the fact that the suggested catchment areas varied in size from 4,133 to 24 square miles, the largest being that of the Yorkshire Ouse, and the next in order the catchment areas of the Trent, Thames, Severn and Great Ouse.
On the long-disputed question of chargeability the royal com mission recommended that rating for drainage purposes should be based, like rates for all other purposes, on annual value. By a wide interpretation of the established principle of "benefit" they proposed that rates should be levied on the whole of a catchment area, but that the rate on the uplands should be pro portionately less than that on the lowlands, the precise amount in each case being determined by the authority subject to con firmation by the ministry of agriculture and fisheries.
One of the difficulties of adjusting the chargeability for works of arterial drainage on a comprehensive and uniform basis is the existence over large areas of a liability ratione tenurae. This in some cases was imposed under old inclosure acts and awards and in other cases dates from time immemorial. These obliga tions are often very difficult to trace, and the land on which they were originally charged cannot now be identified: It is proposed that catchment area authorities should be empowered and directed to commute all such liabilities within their districts either by way of a capital sum or an annual payment. - There already exists a precedent for this course of action in the Somer setshire Drainage Act, 1877.
The subject of arterial drainage overlaps that of the reclama tion of land. Great operations, such as that of the conversion of the Fens in the 17th century, from an immense swamp into a tract of fertile agricultural land, involved the establishment of an elaborate system of arterial drainage. This, like that of Holland, depended for its efficiency on continuous pumping and on effective embankments against the inroads of the sea. Many other areas have been similarly reclaimed and added to the agricultural area, and in all these cases, of ter the initial opera tions, reversion to their original condition is only prevented by the maintenance of a system of drainage, combined very fre quently with the upkeep of sea defence works as the new nodes of the Netherlands in the Zuider Zee. (See also RECLAMATION OF LAND ; CATCHMENT AREAS.) (R. H. R.)