Estuary History

The following text is taken from a Report entitled 'The Humber Estuary - A selection of papers on present knowledge of the estuary and its future potential given at two symposia arranged by the Humber Advisory Group and the University of Hull' dated 20 January 1979.

Synopsis

NV Jones, Department of Zoology, University of Hull

History

The Humber has been formed by the amalgamation of several rivers running from West to East, breaking through the chalk wolds and later being forced into a south-easterly direction by an ice front. The development of the existing drainage system and more recent changes in the course of the main channels resulting from natural changes and man-made developments are discussed by de Boer in Chapter 1.

The movement of channels within the Humber Estuary is a continuing process. In the upper Humber, channel migration tends to be faster than further downstream and important changes which have taken place since the beginning of the century are discussed by Denman in Chapter 2.

In the lower Humber, the present main channel is similar to that shown on the earliest English chart with soundings, dated about 1560; changes in sea level have, however, caused significant changes in the configuration of the coastline in this region. For example, the area from Sunk Island to Spurn had settlements in pre-Norman conquest times but these were abandoned when the sea level began to rise late in the 13th century leaving a shoal - Sunk Island. A reduction in the rate of rise of sea level in the 17th century stimulated reclamation activities during which Sunk Island and Cherry Cob Sands were recovered. Shoals in the upper estuary have also been the basis of the reclamation of both broomfleet Island and Read's Island in the 19th century.

Spurn Peninsula is an unusual feature of the outer estuary and historical studies show that the present spit is the fifth for which records exist. Previous spits seem to have followed a cycle of growth and destruction lasting about 250 years; artificial stabilization has however prevented, but only just, thedestruction of the present spit for 100 years longer than might otherwise have been expected.

Physical features

The main approach channel to the Humber leads through New Sand Hole and divides into three channels south of Spurn Head: Hawke Road, Bull Channel and Haile Channel where depths vary between 9 and 16 meters at Low Water. West of Grimsby the channels merge to give deep water (12-19 m at Low Water springs) exploited by the Immingham Oil Terminal. The channel then crosses to the north bank at Hull where Low Water depths are 9 m or more. As indicated above, these outer estuary channels have been relatively stable for a long time but those to the west of Hull are much less reliable with the main navigable channel changing from the south side of Read's Island to the north bank and back again with a cycle time of up to 20 years.

The British Transport Docks Board1 accumulated a great deal of physical data which was used in designing and operating a large model of the estuary for research purposes. Unfortunately this model is no longer functional2. Some of the data quoted by Denman in Chapter 2 are summarised here to give a general idea of the dynamics of the estuary.

The tidal cycle in the outer estuary is nearly sinusoidal with a 6.25hour ebb and flood component. At brough, however, the ebb tide extends over 8 hours and the flood for 4.5 hours. The volume of water passing Spurn Head during a spring tide is about 1.7 x 109 m2 but only 60 per cent of this during a neap tide. The freshwater input averages about 246 cumecs with an increase to about 1 550 cumecs at times of flood, The Humber is generally a well-mixed estuary with salinity varying by less than 5 per cent with depth. On a winter spring tide there can be as much as 3 x 106 tons of silt carried in suspension but only about a third of this would be suspended during a summer neap tide. This suspended load varies with position in the estuary and stage of the tidal cycle, it is also affected by temperature arid freshwater discharge.

  1. now Associated British Ports (ABP)

  2. This is a reference to the physical model of the Humber Estuary that once stood on the site of what is now Port House, ABP’s local headquarters. A wholly-owned subsidiary of ABP, ABPmer, continues to operate a mathematical model of the estuary at its base in Southampton.

The substrata of the intertidal areas are predominantly muddy but the central bed is mainly fine to medium sand with some local gravel and boulder clay exposures. The movements of the sediments both within the estuary and in the adjacent parts of the North Sea require further investigation

Chemistry and pollution

The Rivers Ouse and Trent contribute an average daily flow of 246 cumecs to the Humber of which about 14 cumecs are sewage effluent and 12 cumecs are trade effluent. A further 2.5 cumecs sewage and 3.1 cumecs trade effluent are discharged directly into the Humber.

The regional water authorities (Anglian, Yorkshire and Severn-Trent) and their predecessors have been monitoring several chemical and biological parameters and such surveys are planned to continue. In Chapter 3 Urquhart summarises the work that has been carried out and also draws attention to the production by the Water Research Centre of a one-dimensional time dependent model for the estuary which, it is hoped, will provide a basis for the future management of the tidal waters.

Dissolved oxygen rarely falls below 50 per cent saturation in the middle and outer estuary but in the area to the west of brough it is very variable, the range recorded being from zero to supersaturation. This oxygen sag in the upper estuary is a long-standing one and possibly partly natural; it has however been improving in recent years, a situation which can be correlated with improvements in the condition of the River Trent.
Extreme values of oxidised nitrogen range from 0.4 mg 1-1 at Spurn to 12.0 mg 1-1 at Trent Falls. Ammoniacal nitrogen in the Ouse and Trent has shown a decrease since 1964 which is related to an associated increase in oxidised nitrogen. Levels of ammonia at Killingholme have however remained more or less constant at 0. 1 mg 1-1.

Heavy metal analyses of estuarine water have posed some practical difficulties but records are kept of metal levels in both sediments and organisms, particularly with respect to certain discharges. Determinations of copper, zinc, lead, cadmium and iron carried out by L. H. Jones and discussed in Chapter 4 showed considerable variability between species, seasons and different years. Generally, organisms in the Humber carry metal loads similar to animals from estuaries classed as reasonably unpolluted with respect to these elements. Metal levels in sediments and organisms were generally higher from within the estuary than from the coastal regions outside, but no study was made of the relationship between the levels recorded and the nature of the sediments.

Biology

Both benthic and intertidal surveys (see Urquhart, Chapter 3, and Jones and Ratcliffe, Chapter 5) have shown the expected increase in diversity of animal life from the freshwater to