The Middle Medway Sub-catchment
The Middle Medway is a complex sub-catchment covering an area of 579 km2 from the Upper Medway's confluence with the River Eden, west of Tonbridge, to Maidstone where the river becomes tidal. This means that the Middle Medway includes 13 Water Framework Directive (WFD) waterbodies, all of which are at moderate status or below.
The Middle Medway includes several large population centres like Tonbridge and Maidstone. Several large trunk roads and motorways also cross the region.
Alder Stream and Hammer Dyke - The catchment is formed of a number of small streams and ditch systems and has two distinctive characteristics; to the south it is sleep sloped and wooded whilst to the north it is low lying and greatly controlled by the water levels within the River Medway which makes its northern boundary. In the south the geology is Ardingly Sandstone with Lower Tunbridge Wells Sands. The streams have cut through these layers and exposed the Wadhurst Clay. Consequently, there are many springs which coalesce to form the main streams. In the north, the Clays (Wadhurst or Weald) have been overlain with Alluvium and River Terraces. This variability gives different permeability and so parts are heavily drained whilst others can be relatively dry. Mainly run-off fed the streams can be flashy in nature and prone to flooding.
River Bourne - The river rises on the Greensand ridge within the parish of Igtham, and flows in a south easterly direction joining the River Medway upstream of East Peckham. The river flows mainly over Wealden clay and is fed mainly by run-off.
The river ecology shows signs of stress from low flow conditions in the upper reaches and is heavily impacted by the large number of modifications as a result of historic milling activities. A number of large mill ponds along the course create large still water habitats and interrupt the natural river processes and fish migration within the catchment.
Ditton Stream - The East Malling/Ditton stream rises from a distinctive spring near East Malling. This spring is created from the junction between permeable Folkestone Beds and the more clayey Sandgate Beds. The underlying Hythe Beds are highly fractured in this catchment and it is likely that this geological layer is also adding to the spring flow. There is no permanent measure of flow within the catchment; however the lower greensands help to sustain flow even during drought conditions.
The course of the Ditton stream has been greatly altered by man. At its headwater, it immediately passes through an ancient mill and along its course the stream is culverted under railways and many roads including the M20 before it reaches its outflow into the tidal stretch of the Medway. Historical changes for milling purposes and aesthetics have left a legacy of impoundments, canalisation and online lake with little of the streams natural hydrogeomorpholgy still present.
River Len - The Len gains from chalk springs at Lenham but the majority of the catchment is comprised of the Greensand Formation. Gault clays to the north of the water body mean that river flows can rapidly react to elevated rainfall events. The river catchment contains widely varying land uses. The upper and mid reaches are more rural, whereas to the west, the river is heavily urbanised, with many weirs, impoundments and culverts.
The river passes through two notable sites, Leeds Castle and Mote Park, as both sites historic online lake features have been created interrupting the natural course of the river. However as a result wet wood and meres were historically created to help manage siltation of the lakes and these have created important habitats which supports a diverse range of wildlife.
Leybourne Stream - The stream currently runs south from Trottiscliffe, under the intersection of the M26 and M20 then east parallel with the M20 into Leybourne and from there north under the M20. The stream then runs along the western edge of the series of Leybourne lakes and into a confluence with the Medway near Snodland PaperMill.
Within the lower reaches the stream supports a population of water vole and a number of fish species including pike and eel, however fish migration is limited by a large structure at the confluence with the Medway which is likely to be affecting recruitment.
Loose Stream - The source of the loose stream is located in Langley, it then flows through the villages of Boughton Monchelsea, Loose and flows into the River Medway at Tovil. It has a reputation for having the highest concentration of mills in any river in Kent, historically 14 mills were located along the length of the stream resulting in the steep sided stream with several mill ponds we see today.
Coxheath Waste Water Treatment Works (WWTW) contributes to phosphate loading in the Loose. Historically, Southern Water has made substantial investments in treatment facilities at Coxheath, starting in 2000 when the works was completely rebuilt. Since this time the works' performance has been good and the overall impact on the stream has reduced. The amount of phosphorus discharged has increased over the years with population served. This was because the 2000/2007 treatment schemes tackled ammonia and biochemical oxygen demand rather than phosphorus. It is worth noting that ammonia is now in "high" status as a result of this work.
Mereworth Stream - The Mereworth Stream sources from Swanton valley north of Swanton village, running south east, past Mereworth School, and Mere House. After crossing under the A26 the stream runs towards Brewers Hall farm and towards Pizien Well, south of the stream stands Mereworth Castle . After Pizien well the stream runs south of Manor farm and along the southern edge of Wateringbury, past the eastern edge of Wateringbury school to a confluence with the Medway around Bow Bridge and Wateringbury station.
Much of the stream runs through a mix of private land and agriculture land with the western end bordering the urban areas of Wateringbury.
Historically a mill stream with seven mills running the length of Mereworth stream, evidence of those remaining includes the historic site of Mereworth Mill, now located by a waterfall at the far eastern end of Mereworth Castle, Brattle (Upper) Mill and Warden Mill near Warden Farm.
Mereworth stream currently attains a moderate status in the Water Body Assessment, although lack of proper assessment of fish migration and phytobenthos makes a full assessment of the stream under the Water Framework Directive difficult.
Penn Stream - Penn Stream runs north to south from Starvecrow woods through the eastern edge of Tonbridge. The Penn stream then runs along side Hugh Christie Technology college, Higham Wood and under the A26 Hadlow Road. The stream then joins the Medway River at a confluence near Postern Park.
Tudeley Brook - The Tudeley Brook, also known as the Pembury stream runs from east of Pembury northwards to its confluence with the river Medway near East Peckham. The stream runs over sandstone and clay rocks, its headwaters receiving flow from a number of springs in the Tunbridge Wells Sand formation. Land use is predominantly grassland and orchards in its headwaters and arable further downstream. Paddock Wood in the centre, and part of Pembury, are significant urban areas in the water body.