Natural Area Profile - River Hull and riparian fringes
Rising from natural calcareous springs around Driffield, the River Hull runs its course southwards to join the River Humber at Hull. The River Hull valley dominates the western
landscape of Holderness and both the river and its adjacent wetland habitats support a diverse range of plants and animals.
The upper tributaries of the River Hull originate on the edge of the Yorkshire Wolds and enter an alluvial flood plain with drift deposits of glacial till and occasional pockets of sand and gravel within a few miles of their source. This surface geology influences the character of the river with gravel, sand and silt sediments deposited on the riverbed in varying proportions. This variation in the riverbed sediments is reflected in the species composition of the aquatic vegetation which is abundant throughout the headwaters during the summer.
In recognition of its importance as the most northerly chalk stream system in Britain, the head waters of the River Hull have been designated as a SSSI. Species characteristic of the upper reaches of the Hull are stream water crowfoot, lesser water parsnip, mare's-tail, spiked water milfoil, fennel pondweed and shining pondweed in the channel, whilst the marginal vegetation is often composed of branched bur-reed, common reed, reed canary-grass and reed sweetgrass.
Opposite-leaved and flat-stalked pondweeds occur locally, with river water-dropwort occurring in the middle reaches. The latter is a scarce species at the northern limit of its British range here; it is endemic to Norther Western Europe and of highly restricted occurrence outside the Britain and Ireland. The aquatic and emergent marginal vegetation provides habitats suitable for a diverse invertebrate fauna including several uncommon species.
Otters have recently recolonised the upper reaches of the River Hull and its headwaters, with increasing evidence that this species is now well-established once again. The once-familiar Water Vole is, however, confined to a very few isolated populations. The invertebrate fauna of the river is also of interest with notable species including the uncommon mayflies Heptagenia fuscogrisea and Caenis robusta.
Associated with, and influenced by the river are riparian habitats that are of great value for wildlife. For instance species-rich wet grassland and marsh is still quite extensive in the upper reaches, particularly between Driffield and Wansford. Further consideration will be given to thes habitats in the next section.
Reflecting this diversity of habitat, the river valley supports a diverse breeding bird community, including several waders such as lapwing, snipe and redshank, wildfowl, particularly mallard and mute swan, together with yellow wagtail, sedge warbler, reed warbler, reed bunting and many more widely occurring species.
As the River Hull runs further south towards Beverley and Hull, the river becomes tidal in nature with an associated increase in salinity. In these lower reaches the river is enclosed by floodbanks to protect adjoining farmland and settlements. Although still forming a focus for bird movement, the river has little associated natural habitat remaining. One notable exception is at Pulfin Bog SSSI, where a seasonally flooded and spring-fed reedswamp has formed in a major bend of the river channel.
Key nature conservation features
- chalk stream headwaters
- flood plain grassland and marsh
- remnant reedswamp
- alder and willow carr
- breeding birds
Key issues:
- maintenance of water quality
- nutrient-enrichment from adjacent land-uses, including agriculture, watertreatment works, fish farms
- river engineering and flood defence
- water abstraction from aquifer and surface - waters
- recreational pressure including navigation and angling
- overgrazing of banks and bankside habitats
- loss of riparian habitat to competing land uses
- channel maintenance including desilting and weed-cutting