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E n v ir o n m e n t A g e n c y
NATIONAL LIBRARY & INFORMATION SERVICE
SOUTHERN REGION
Guildbourne House. Chatsworth Road, Worthing. West Sussex BNII 1LD
a I Ri vers Authority uthern Region
Guardians of the Water Environment
_ A G E N C Y
054487 the North to the South. The rupted this river system when leaving the nearby River Itchen THE oldest rock is the Cretaceous the sea breached a ridge be unaffected. The net result is Chalk, a porous, fine grained tween the Isle of Wight and that water taken from the river limestone which outcrops over Purbeck. Southampton Water for public supply is subsequently RIVER the whole o f the valley to the is a drowned, low-lying valley returned in high quality and in North o f Eastleigh. Rain soaks dating from that time. the same general location from ITCHEN into the chalk rock rather than which it was taken. running off and then gradually The NRA sets stringent con percolates through the pores WATER ditions on the quality and quan or small fissures under the in tity of all permitted effluents to fluence o f gravity until it issues QUALITY ensure that river and ground COURSE AND from springs in the valleys. The water quality are preserved to chalk thus forms a massive The remarkably high quality o f high standards. The standards GEOLOGY natural underground reservoir natural chalk streams owes for rivers are known as Environ or aquifer. Chalk rock is in much to the geology. Rain is mental Quality Objectives. The River lichen is perhaps the itself split into three main sub filtered by the chalk as it per Altogether 55 km of the River best example of a chalk ground divisions, these being the colates through to the under Itchen and its tributaries above water fed river that exists Upper, Middle and Lower ground reserves. The crystal Eastleigh have an objective of anywhere in the world. It rises Chalk. Most of the catchment clear springs have an almost Class 1A (water of the highest on the Upper Chalk as three is Upper Chalk but there is an constant temperature, varying quality, suitable for potable spring-fed tributaries; the inlier of Lower Chalk in the little with the seasons. The supply abstraction, game and Candover Stream, the River St. Catherine’s Hill area to the quality of chalk stream waters, other high class fisheries and of Aire, and the Cheriton Stream. East o f Winchester. coupled to their hardness and high amenity value). Between These flow from three points It is the very permeable alkalinity, accounts for their Eastleigh and the tidal limit o f the compass to unite just chalk with its natural storage capacity to assimilate effluents. there is a 4 km length of river West of New Alresford. capacity that gives the river its This capacity is important in which has an objective of Class The accepted source is at special character. The river has South Hampshire where there IB (high water quality, suitable Kilmeston just South o f New few tributaries and these seem has been continuing develop for game and high class Cheriton. This stretch of the to fail on a right angle grid pat ment based on good communi fisheries). The downstream river before it joins the other tern, reflecting the structure of cation links. tributaries, the Monks Brook, tributaries is known not only the underlying chalk. The Increases in population have Allington Lane Stream, and Bow as the Cheriton Stream, but as shape o f the river (drainage resulted in three large sewage Lake are also Class IB. To ensure the Upper Itchen or the Tich- pattern) contrasts sharply with treatment works discharging that quality objectives are met, bom e. It has been suggested that o f rivers on impermeable directly to the lower and tidal the NRA limits the strength and that the River Meon upstream clay catchments, such as the reaches of the river. The largest quantity of effluent and pre of Wamford was once a tribu River Medway, where rainfall is the Chickenhall sewage treat scribes a minimum residual tary o f the River Itchen and flows overland, creating a host ment works at Eastleigh which flow for the river (the lowest was later captured by the o f tributaries with a branching has a consented dry’ weather flow which will not prejudice Meon which had the advantage pattern. Chalk streams are flow of up to 30,000 mVd. The its well being). This prescribed of a more direct route to therefore described as having a two others at Portswood and flow is set to give a satisfactory the sea. low drainage density, whereas Woolston discharge to the dilution for effluent as well as From Alresford the river for Wealden rivers the density estuary’ and have consented dry being sufficient to attract flows West to Winchester is high. weather flows of 27,700 m3/d salmon and sea trout into the where it collects the Nun’s From Eastleigh to the sea the and 15,000 mVd respectively. estuary’ and to enable them to Walk Stream from the North river flows over younger sands, Above Winchester, near Hcad- pass upstream. At times of low West. It then flows southwards silts and clays of Tertiary origin. boume Worthy about 4,100 flow, the NRA pumps under through the outskirts o f East These are much more imper mVd of treated effluent are dis ground water into the head leigh collecting a small tribu meable than the Chalk. charged to the river. waters to support the river and tary, the Bow Lake which The landscape of the Itchen Sewage from Winchester is to achieve the minimum resi drains from Fishers Pond to the catchment was sculpted in the cleansed, after settlement, by dual flow. This is particularly East. The river enters the tidal last Ice Age. Although it is un utilising the natural properties important to ensure that the estuary at Woodmill where it is likely that the ice sheet reached of the chalk and over 9 Ml/d water quality below Eastleigh is also joined by the Monks so far South, the ground would (2 mgd) of effluent reaches the maintained at a sufficiently high Brook. This principal tributary have been frozen. Under these river by an unusual and indirect standard to be abstracted for drains the expanding conur permafrost conditions, frost route. The very fine grain public water supply above bation o f Chandlers Ford, East action and rapid runoff from nature of the chalk allows settled Swaythling. leigh and Swaythling. The total rainfall would have shaped the sewage to be discharged to the catchment area o f the Itchen is dry valleys that exist today. ground by the ‘soakaway’ 400 sq. km, o f which 360 sq. At that time the Itchen is method. The chalk is an excel HYDROLOGY km is chalk. In addition Monks thought to have been a tribu lent physical and biochemical Brook drains a catchment o f tary o f the ‘Solent River’ which filter, removing viruses, bacteria, AND RESOURCES 49 sq. km. flowed from the River Frome and organic load almost entirely’ The underlying rocks form in Dorset to Littlehampton and reducing inorganic pol Annual rainfall varies from part o f the northern flank of when the Isle of Wight was still lution significantly. The effluent about 750 mm in the South of the geological structure known connected to the mainland. A has been discharged to the the catchment to more than as the Hampshire Basin. Its sea level rise of 45 metres ditches on the side of St. Cath 900 mm in the North, giving an rocks slope gently, or dip, from some 10,000 years ago dis erine’s Hill for over 100 years average rainfall of 875 mm per annum. In the summer the evaporation always exceeds the rainfall, hut in the winter the rain percolates down through the chalk and moves underground to springs in the river valley, a process that may take many months. The maxi mum flow in any year is typic ally only 3 to 4 times the minimum, unlike most of the Wealden rivers where the ratio can be as high as 500 to 1. Underground reserves of water which saturate the chalk are known as aquifers. The NRA collects information about the levels of groundwater hy taking measurements from over 250 wells and boreholes in the area. The Rivers Test and Itchen provide much of the water used for public water supply in Hampshire but about 21,230 Ml (4,700 million gallons) are pumped annually by Southern Water Services Ltd from bore holes sunk into the chalk aquifer at Otterbourne. There are smaller groundwater abstrac tions at Totford, Easton, Winchester and Twyford. The water quality is extremely high and little treatment is required. At Otterboume, Southern Water also abstracts up to 45 Ml/d (10 mgd) of river water. Similarly at Gaters Mill, just near the M27, Portsmouth Water Company abstracts up to 45 Ml/d (10 mgd). This is several kilometres downstream of Chickenhall sewage treat ment works, so that the effluent is well diluted by the river and is partly reabstracted. The licences which permit water to be taken at these loca tions are known as ‘Ijcences of Right’ because the abstractions existed before the Water Resources Act ( 1963). This Act was the first attempt to preserve the quantity of water in the environment in England and Wales. At that time established abstractions were licensed to continue taking the same amount as previously and at the same location. There are a number of licensed private abstractions within the catchment. Most are for general agricultural pur poses, but a small number are for spray irrigation and indus trial use. K (?A kv::
Applications for abstraction means o f boosting river flows in species of invertebrates have licences must be made to the impermeable catchments such been recorded horn the River NRA which considers the as the Medway and Ouse. Itchen. In consequence there potential environmental effects Groundwaters collect rain over are fine brown trout fisheries and any effects on other lawful a far larger area and to a greater throughout the upper and water users. Licences which are depth, they do not suffer from middle reaches o f the river. granted normally impose re evaporation, they supply high From its source to Bishop- strictions which ensure that quality, cool water free from stoke the river is designated as a water is only taken from the the algal growths that trouble salmonid fishery under the EEC right places and at times when surface reservoirs and their Fisheries Directive which rein it can be spared. development does not affect forces the duty to ensure that One important consider the landscape. water quality objectives are Salmon rearing ation is whether water will be The NRA monitors river met and secures the free pas for dace, roach, perch and gray exported from the river system flows using specially designed sage of migratory fish into and ling, principally between or ‘consumed’. Some uses such gauging weirs. There is an ultra within the river. Woodmill and Gaters Mill on as spray irrigation, evaporative sonic flow gauge at Riverside The lower reaches are an the East bank, although the cooling or bottling mineral Park above Woodmill and con important rod and line fishery fisheries are privately owned. water are almost entirely con tinuous flow gauging stations for salmon and sea trout, which sumptive. In the case o f public near Allbrook and Easton, and enter the tidal river early in water supply and general indus on each o f the three upper trib spring, depending on rainfall FLOOD try, about 80% o f the water is utaries. The longest flow record, and flow. The main upstream returned to the river. dating from 1959, is at Allbrook spawning migration is generally DEFENCE Watercress growing, fish (which roughly coincides with at the end of the fishing season. farming and non-evaporative the Chalk/Tertiary geological The eggs are laid in gravel nests For much of its length, the cooling return almost all o f the boundary) where average flow known as redds, mainly between River Itchen is not one stream water at the same point from is 5 3 m3/sec. Bishopstoke and Winchester. but two, three or even four which it was taken, so the over Woodmill, at the top o f the separate channels running all effects on flow are small, tidal Itchen estuary is the site o f parallel to each other. The despite the large quantities FISHERIES an ancient salmon net fishery braided channels and cross involved. In all, there are six with private rights pre-dating channels have a considerable teen watercress farms in the The salmon and trout fisheries Magna Carta. In 1979 a new fish number of structures to regu Alresford and Micheldever area on the River Itchen are among pass with an electronic fish late flows and levels. These accounting for. about 25% of the finest in the South of England counter was constructed to result in a very controlled river UK production. There are four and the fine trout fisheries o f record the passage of migratory with high retention levels. commercial fish farms on the the upper and middle reaches fish. Many sluices are operated by upper reaches of the Itchen have been managed by riparian The NRA uses the data to riparian owners though some, at sites near Itchen Abbas, owners for hundreds o f years. establish the size of the salmon such as the automatic outfall Avington and New Alresford. population in the lower reaches sluice at Woodmill, are owned In order to preserve the river of the river. Another fish pass and operated by the NRA. in the face of the wide range of and counter at Gaters Mill near Three historic uses of the demands for water and for the the M27 enables fish m ove river gave rise to this multipli disposal o f effluents, the NRA ments to be related to environ city of channels, these being and its predecessors developed mental variables such as river the harnessing of water power two groundwater schemes to flow, daylight conditions or for milling, the use of water boost river flows when neces water temperature. This will be meadow systems to promote sary. These utilise water from an invaluable aid to preserving the early growth of pasture, and boreholes in the Candover and the salmon and sea trout fishery the development of the river Aire catchments. in the face of future demands for navigation. The schemes take advantage on the river. Traditional water-based ind o f the time lag between rain fal Young salmon are bred and ustry included wool processing, ling on the Chalk Downs and it released to the headwaters to paper making, tanning, flour finding its way to the water enhance stocks. Since 1985 and grist milling, as well as the table. Underground water these ‘parr’ have been implanted generation of electricity. The reserves reach their peak when with microtags to help the NRA last working mill ceased opera river flows are declining at the Chalk streams are renowned develop a better understanding tion in the 1960s. onset o f summer. By siting bore for the abundance and diversity o f the movements of migratory The valley floor contains evi holes at sufficient distance from of water life on which fish feed. fish when they leave the river dence o f extensive systems o f the river and piping the pumped Unlike the soft, acidic waters o f and go to sea to feed. Adult fish surface irrigation, the true water to the river, winter rain the Wealden streams, chalk carrying tags have since been ‘water meadows’. High level fall can be ‘borrowed’ to water provides ample calcium recorded off the West o f Ireland ‘carriers’ (which often still enhance low summer flows. with which shrimps, snails and and in home waters. exist) supplied water to the Groundwater was used in this other creatures can build Radio tracking of 36 salmon meadows which were drained way in the drought years of external skeletons. Some eight tagged with micro-transmitters via low level channels. For 1976, 1989 and 1990. species o f stonefly nymphs, was carried out in 1990 to many reasons, including re Groundwater schemes have twenty species o f mayfly study migratory fish behaviour duced demand for early pasture, many advantages over surface nymphs, thirty-eight species o f in the estuaries. the systems have become dere reservoirs which are the only caddis and sixty-seven other There is some coarse fishing lict. Between Winchester and Shore, circa l^OO. Hampshire', byR. Murdie, and REFERENCES Canals o f Southern England', by Eastleigh, the former Itchen The Hampshire' collection, Surt>ey o f Agriculture o f Hadfield. Winchester City Reference Hampshire '(Vancouver). Navigation flows parallel to, or Inform ation on the Candover Library. coincident with the river. In The Dorset volume of'Land and Aire Groundwater Schemes the 12th Century the river was Proceedings o f the Hampshire Utilisation Surt
More recently some urban J ^ l l l n s t w i L o rw S t r e a m ^ . ■ Claygate Beds and areas have flooded, particularly London Clay on the Monks Brook which drains mainly from sand and 'S/S/ r a Chalk clay soils. The Brook flooded four times in the first half of this Tunbridge Wells Sand. century. Following serious Wadhurst Clay and S * / Ashdown Beds J flooding in Chandlers Ford and Southampton Water Swaythling in I960 a scheme was carried out to improve the Sections showing the general relations of the rocks along the lines Y—Y' drawn on the map flood carrying capacity of the Brook. Portsea Ports Down Chichester Ryde Spithead Island Antkline Syndine Petersfleld The NRA and riparian owners 0 .0. dear weed on the Cheriton Stream and the River Aire in order to control stream levels and prevent flooding. Conjectural base of recent deposits
National Rivers Authority Southern Region Headquarters Guildboume House Chatsworth Rood Worthing WestSussex BN11 1LD Purbeck and Portland Claygafe Bed* and Upper Greenland Beds. Kimmeridge 0 10 2 0 km and Gault (0903) 820692 March 1991 □London Cloy and Oxford Cloy