Portrack Sewage Treatment Works lie on a 24.8 ha site adjacent to the River Tees that has historically been occupied by marshland. The potential wildlife value of the non-operational part of the site was recognised not long after the construction of the works began in 1980. There was a series of shallow pools on this land, ideally suited to a variety of waders and other waterbirds. The wildlife interest of this site has been promoted by Northumbrian Water Limited (NWL) since the early 1980s, with appropriate site management undertaken by the Tees Ringing Group with the help of other local conservation groups.

In the early 1990s a more rigorous discharge consent was applied to the site, requiring the works to be up-graded. The necessary additional secondary treatment facilities required extra land which meant encroaching upon the marshland area. At about the same time the northern margin of this spare land was given to one of NWL's subsidiary companies to develop as the site for an incinerator (which, in the event, has not received planning permission on the grounds that the facility is not required). The combined effect of these two proposals was to reduce the size of the wildlife area from c.13.5 ha to c.4.5 ha. However, the company were keen that the remnant land should be used to retain the existing wildlife interest. The design of the modified works was very compact and arranged such that the loss of open water was minimised. In addition, new areas of open water were excavated elsewhere on the remaining area of non-operational land to compensate for the losses; the total area of standing water may now actually be larger than it had been prior to the improvements, while the inclusion of islands in the main Pool A (see Figure 17.1) should make them more attractive to breeding waterfowl. Some of the spoil resulting from this excavation work has been used to create an earth platform and screened approach for a viewing hide.

i) to advise on the development and management of Portrack Marsh;

ii) to formulate and update a Conservation Management Plan for Portrack Marsh;

iii) to advise on the implementation of the Conservation Management Plan;

iv) to report annually to NWL.

The members of the group have endorsed a management plan that clearly states: "Much of the area may be required.for future extension of the treatment works to comply with any new water quality standards". In addition, NWL can use the forum to keep members aware of any proposals that might affect the site. Thus, should the need to develop the site arise, all parties should be sympathetic to NWL's requirements.

Figure 17.1 The layout of Portrack Marshes before and after a major modernisation scheme implemented at Portrack Sewage Treatment Works during 1992-93.

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The infrastructure associated with the brining operations occupy only a small proportion of the total area; the flat, low-lying land is crisscrossed with pipelines and access tracks and dotted with occasional well-heads. Amongst these man-made structures is a variety of wetland habitats: pools of various sizes, reedbeds, swards rich in orchids, ditches and extensive areas of grazing marsh. Of particular interest are the scattered pools, which tend to vary in salinity from brackish to highly saline, owing to brine spilling from the well-heads. These pools support a rich saltmarsh community; 20 different species of halophytic plant have been recorded on brinefields 4 and 5, having colonised presumably from the nearby Tees Estuary. The pools are also very attractive to waders; thirty-five species have been recorded. The wader species found feeding on pools vary according to their salinity. Some pools are hyper-saline and support a very limited range of invertebrates confined to chironomids and brineflies (Ephydra, Diptera). However, these insects are very abundant during the summer months and can provide a valuable food source for some of the smaller waders, such as Ringed Plover, Dunlin and Little Stint. Larger wader species generally prefer larger prey which can be found on less saline pools, thus reducing competition between species. Good numbers of waders nest on the site; surveys in the late 1980s found maxima of 8 pairs of Redshank, 25 pairs of Lapwing, 22 pairs of Ringed Plover, a single pair of Oystercatcher and occasional pairs of Snipe (83 (Appendix 11 - Selected references and further reading)). The site is the most important in Cleveland for Ringed Plover which nest on a variety of artificialsites, including bare, stony areas around pools, hardcore around the well-heads, and unsurfaced gravel roads. As well as supporting a high density of Ringed Plovers, studies suggest that nest survival is higher than average, presumably owing to the lack of human disturbance and the absence of tidal flooding which are a feature of many more natural sites.

The extraction of the brine makes the land liable to subsidence (which is the source of some of the pools) and consequently unsuitable for building development. In recognition of this constraint, together with the site's wildlife interest, ICI have started to implement active conservation measures in line with the broad ranging Company Environmental Standards. Based on the various ecological studies undertaken on the brinefields, a range of conservation action points have been drawn up:

1) Wherever possible, operations are planned to avoid damaging or disturbing the important saltmarsh flora.

2) Wetlands and salinity gradients are maintained by controlled releases of fresh water and brine. New wetlands have been designed to maximise the benefits of having a variety of salinities.

3) Roads and hard core areas are kept to a minimum to limit the loss of habitat.

4) Where access roads and hard core are essential, they are left unsurfaced and with a substrate chosen to maximise their attractiveness to nesting Ringed Plovers, Oystercatchers and Common Terns.

5) All nests found on the site are marked to prevent them from being accidentally destroyed.

6) Grading and road maintenance are carried out in late summer in order to minimise disturbance to nesting birds.

7) Opportunities are sought to add features for wildlife (e.g. islands were created for breeding Common Terns in 1993).

Since 1990, a further brinefield (Number 6) has been developed, which has enabled the company to consider the ecological implications of the process right through from the design stages. An ecologically-based management plan was drawn up for the field prior to development, in consultation with various outside organisations. Not only has this ensured that the new field will be of maximum value to wildlife, it has also avoided costly planning delays and enhanced the Company's environmental reputation. The new brinefield contains a greater area of wetlands than existed before development started. The latest innovation associated with this enlightened scheme has been to re-establish a tidal regime around the well-heads in one operational area, providing valuable additional habitat for waders. In the longer term, the intention is to turn over large areas of this land to nature conservation once the brining operations cease. In 1993, ICI was presented an award by the Royal Town Planning Institute for its environmental work associated with the development of Number 6 Brinefield.

View across part of ICI's North Tees Brinefields showing the matrix of infrastructure and wetland habitats

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Feature 17.3 Tophill Low Water Treatment Works, East Yorkshire (Yorkshire Water Services)

Tophill Low Water Treatment Works not only supply water to the City of Hull but now also offer an excellent wetland nature reserve. The 110 ha site occupies a narrow strip of low- lying land sandwiched between the Barniston Drain and the River Hull. The main features of the site are two concrete-walled reservoirs, which were completed in 1959. Two filter washwater lagoons (described in Feature 12.4 (Chapter 12 - Silt storage lagoons)) and some clay pits provided, until very recently, the only other wetland habitat on the site.

The wildlife interest of Tophill Low has been recognised for many years. Lying close to the east coast of England, the expanse of open water has proved a magnet for migrant birds; a total of over 240 bird species has been recorded. The potential appeal of the site to migrant birds is amply demonstrated by a concentration of over 250 feeding Ruff that took advantage of the bed of a drained reservoir in September 1993. The reservoirs, despite their artificial walls and contours, have, in fact, been notified as a SSSI in recognition of their wildfowl interest. The extensive arable farmland surrounding the site provides feeding for dabbling ducks that roost on the reservoirs, while the shallower 'D' reservoir (c.3.8 m deep) provides a feeding area for large numbers of diving ducks (including up to 800 Tufted Duck). The extent and variety of the wetland complex also makes it of value for other groups of wildlife. An area used for small scale, ad hoc clay extraction, known as East Pond, supports 13 species of Odonata, including the scarce Red-eyed Damselfly and Black Darter, while two locally scarce water plants Greater Spearwort and Nodding Bur-marigold - grow in the South Marshes and washwater lagoons.

In the 1970s a member of staff from Yorkshire Water, together with keen volunteers, formed the Tophill Low Wildlife Group to encourage the development of the site for wildlife. Early projects carried out by the group included flooding a marginal area by blocking a drain and modifying the washwater lagoons. After many years of volunteer input by the Wildlife Group, Yorkshire Water decided that nature conservation should be given a higher profile on the site.

The opportunity to carry out a major habitat creation project presented itself when the NRA came to Yorkshire Water needing clay to carry out flood defence works along the adjacent river. It was agreed that the NRA could extract clay from specified areas within the site and, in lieu of payment, they would re-grade the excavations to form new wetland wildlife habitats. Various fairly large, but irregular-shaped blocks of land towards the periphery of the site were chosen as they offered little potential from an operational standpoint and little value in terms of real estate. The work was carried out between 1990 and 1993, resulting in the formation of the North Marsh, the re-design and enlargement of the South Marsh and further improvements to the filter washwater lagoons. The largest component of these works was the excavation of the two blocks that make up the large, shallow South Marsh. The East block lies on a peaty substrate which made excavation and land-forming difficult. Around the edge is a ring-fence ditch, c.2m deep and c.4 m wide, which prevents the planted Common Reed on the fringe from spreading, while the shallow centre has been formed into a system of ridges and furrows. The value of this new habitat to birds soon became apparent; in 1993 it supported about five pairs of breeding Pochard, at least six pairs of Tufted Duck and a pair of Shelduck. The West block was created in an area that had previously been tipped with clay spoil and planted up with conifers that were of little value to wildlife. This shallow scrape still retains a clay bed over much of its surface area; straw has been introduced to help to develop an organic layer in order to increase the density of invertebrate prey for waders, such as the breeding Little Ringed Plovers. The deeper North Marsh should provide additional habitat for Odonata as well as nesting birds.

Wanting to capitalise on the wildlife potential of the improved site, Yorkshire Water sought the advice of the RSPB on visitor access and facilities, and wardening requirements. As a result of these recommendations, Yorkshire Water increased the quota of hides around the site to nine and, early in 1993, took the enlightened step of appointing a full-time warden to look after the, wildlife habitats and deal with visitors. Schools will be encouraged to visit and the general public allowed to purchase permits giving them access to the trails and hides and helping to offset the cost of employing a warden. In October of that year a splendid new nature reserve was opened.

Aerial view of Tophill Low Water Treatment Works showing how wetlands have been incorporated into most of the marginal areas of the site.