THE PATTERN OF SEDIMENT MOVEMENT IN THE RIVER TYNE David G. HALL B.Sc, PhD., A-M.I.C.E., A.M.I.W.E., Assistant Chief Engineer (Water Resources), Devon River Authority. 1. INTRODUCTION The catchment of the River Tyne is located in the North-East of England, ft drains the eastern slopes of the northern Pennine Chain, the range of hills commonly known as the backbone of England. The catchment area is shown in figure 1. It is situated within the influence of both oceanic and continental type climates and as a result the climate pattern is of a continual series of depressions and anticyclones. Orientation of the catchment is in a general easterly direction. After draining some 1,142 square miles (2,957 square kilometres), the river discharges into the North Sea at Tynemouth. The tidal estuary of the Tyne is some 19 miles (31 kilometres) long, 12 miles (19 kilo­ metres) being navigable to ocean-going cargo vessels, as a result of an extensive pro­ gramme of channel dredging. The purpose of the study described has been twofold: (i) To understand in a quantive manner the magnitude of catchment erosion and its consequent sediment transporc in the rivers and streams through to its deposition in the tidal estuary; (ii) To understand the manner in which the estuarine sediments are moved around under tidal action with the object of more fully understanding the problem of pol­ lution in the estuary of the Tyne. Survey work commenced in 1958 and extended into the summer of 1961. Throughout this time frequent samples of both fresh and tidal water were undertaken in order that the most comprehensive picture possible could be obtained of sediment movements throughout the river system. The sediment survey of tidal waters was undertaken in conjunction with a survey of the tidal hydraulics of the estuary. The work was financed by a committee of Local Authorities in the Tyneside area. II. THE RIVER TYNE CATCHMENT II. 1. Topography The catchment area comprising parts of counties Northumberland, Durham, Cum­ berland and Roxburghshire, is roughly triangular-shaped. The River North Tyne drains in a South and Easterly direction from the Cheviot Hills (1,975 feet) (602 metres), whilst the South Tyne drains Northerly and Easterly from the highest point in the catchment—Cross Fell (2,930 feet) (893 metres). Two miles (3 kilometres) West of Hexham, the two rivers join and flow in an Easterly direction along the Tyne valley to the head of the estuary in the area of Ryton. Between Hexham and Ryton the river is gauged at By well whose catchment area is 834 square miles (2159 square kilometres). There is a second major tributary to the estuary; that of the River Derwent, which drains some 104 square miles (269 square kilometres) of varied landscape in County Durham. This river has only been gauged in its lower reaches since 1963 and hence no records relevant to that river were available during the survey. Gauging commenced at Bywell in 1956 and some six years of records were utilized in analysis. 117 Fig. I — The River Tyne catchment. II. 2. Vegetation The upper courses of both principal tributaries are desolate and rocky and the streams tumble over their stoney beds. The tributary courses of the south Tyne tribu­ taries are more steep than those of the North Tyne. Many of the steep valley sides are scarred by the remains of mineral workings of the last ceraury. The catchment of the North Tyne is more open fell and moorland. About 30% of it is laid out in coniferous forest. The headwaters of the River Rede, a tributary of the North Tyne, feed into Catcleugh Reservoir, the only sizeable impoundment in the whole catchment. 118 The lower courses of the rivers have been rejuvenated. They flow through wide flat-bottomed valleys which are devoted to agricultural pursuits. The Tyneside conur­ bation lies along both sides of the estuary of the river. Housing nearly one million people, it is an area of intense industry varying from shipbuilding, and heavy engineer­ ing through a wide range of trades to the pursuits of a highly successful shipping port. II. 3. Geology Broadly speaking, the geology of the catchment area of the Tyne can be described as a tilted mass of Devonian, Carboniferous and Glacial Tertiary deposits, dipping gradually to the South-East. Superimposed upon this structure is a shallow syncline which spans between the volcanic Cheviot dome and the uplifted Bewcastle dome. The movement of the area against the more rigid Alston Block centred around Cross Fell has given rise to faults which considerably dislocate the simple succession of the strata. The area is criss-crossed by a series of igneous dykes. The oldest strata are found in the North Tyne area and the extreme West of South Tyne and in general the strata become progressively younger in the direction of river flow. The principal rocks outcropping in the North Tyne are shales, carboniferous lime­ stones and sandstones. Some of the thicker carboniferous bands have been worked in times past. The millstone grits form the bulk of outcropping rocks in the South T^ne and Derwent areas whilst the Permian series of dolomites and magnesian limestones form a narrow belt along the coast. Glacial cover was widespread over the whole of Northern England and it is of extreme interest in this study since much of the material eroded by the river in its present state of development originates from the coccurrences during glacial periods. The principal glacial movements have resulted in drift cover up to 2,000 feet (610 metres) in the Cheviots and 1,250 feet (380 metres) in the lower eastern areas. Glacial flow has brought erratics from the Lake District and from South­ ern Scotland. Considerable gravel deposits lie in the valleys of the Rivers Allen and the South Tyne and Lower Tyne itself. The most recent deposits are those of peat. It has formed mainly on the high fells in thicknesses varying from eighteen inches (40 cm) up to six feet (180 cm). The activities of the forestry commission have done much to disturb the formations of peat over the wide areas of the North Tyne Fells. II. 4. Precipitation The Tyne catchment lies in the path of the prevailing south-westerly winds which blow from warmer latitudes gathering moisture as they cross the expanse of the Atlantic Ocean. The Pennine Chain of hills gives rise to a very pronounced orographic influence in the resulting rainfall pattern. Figure 2 illustrates this point. Only a small proportion of the total rainfall is of a convectional nature, but thunderstorms do occur mostly in the summer months. Many can be violent and result in considerable erosion from more unprotected land surfaces. The annual distribution of rain in the Tyne catchment is as follows: Jan. Feb. Mar. Apr. May June July Aug. Sep. Oct. Nov. Dec. 4.2 3.0 2.7 2.6 2.7 2.6 3.8 4.1 3.7 4.2 3.9 3.6 (inches) 107 76 69 66 69 66 97 104 94 107 99 91 (mm) Average for catchment = 41.10 inches (1,045 millimetres) per year. Much of the rainfall, originates in the west, and such falls are readily reflected in rapid rises in river level. The area is also subject to prolonged periods of easterly winds which are sometimes rain bearing. Rain is much lighter, but often very prolonged. In 119 Fig. 2 — River Tyne —• annual isohyets. the winter-time, easterly winds frequently bring snow and periods of very bitter weather. Rain days average 170 in the East and 220 per year in the West of the area. Mean annual evaporation is about 17 indies (430 mm) per annum and snow cover is limited to an annual duration of about 20 days at lower altitudes to an average of 80 days on the hills. 11. 5. Runoff Up to the time of the survey, the Tyne catchment was very sparsely gauged. Since 1960, there has been considerable improvement in the amount of flow data which has 120 become available due to the efforts of the ihen Northumberland and Tyneside River Board. The records of the gauging station situated at Bywell were extensively used in the survey. Bywell, the principal gauging station on the river Tyne at a height of 53 feet (16 metres) above sea level, was established in 1956, to record river flows from the. catchment of 834 square miles (2159 square kilometres) at a point eight miles (13 km) above the tidal limit of the river. The gauge measures discharge from 73% of the total river catchment west of Tynemouth. The flow distribution pattern is shown by the flow duration diagram in figure 3 indicating a comparatively even distribution of flows between the lowest recorded flow of 121 cusecs (3.4 cumecs) (1959) (0.144 cusecs/ square mile) (0.0016 cumecs/sq. km), return period rive to seven years, and the highest recorded flow of some 40,000 cusecs (1,150 cumecs) with a return period of roughly ten years. Mean discharge at By well during the years 1956 to 1964 was 1,452 cusecs (41 cumecs) (23.4 inches) (592 mm) with a modal discharge of 210 cusecs (5,9 cumecs). The sepa­ rate duration curves for summer and winter flows are given in figure 4. Fig. 3 — Flow duration curve — River Tyne, Bywell. 121 ,i- y * 1 t*i-.V <w.f*'ie*i \ 1 • J J 14 *•- -1 t« i* » 1 1 » JW> • 1- »r ' ,» ^»»r - •' - ,: -r- 1 » J •• » TT- Fig.