Volume 1

Survey of the river Tees.

  • Great Britain. Water Pollution Research Board
Date:
1931-1937
Catalogue details

Licence: Public Domain Mark

Credit: Survey of the river Tees. Source: Wellcome Collection.

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    FRESH WATER OBSERVATIONS Movements of the water in the tidal estuary are obviously affected by varia- tions in the flow of fresh water coming down the river. Before carrying out current and tidal observations below Stockton, it was therefore necessary to arrange for continuous observations to be made of the fresh water passing down the river at some point above the tidal limit. For this purpose a water level gauge was erected at Croft Bridge, which is about 17 miles above the tidal limit. The river at this point is not ideal for the current observations, which were carried out over a measured distance of 100 yards just above the bridge. There is a bend in the river immediately above the measured distance, and this bend is accentuated when the:water level rises, so that accurate results were at times difficult to obtain. This, however, was the best place that could be found below the junction of the River Skerne, and it possessed the advantage that a level gauge could be erected on the bridge, which is one of the few structures across the river, the columns or supports of which do not wholly dry out when the river is low. The zero of the gauge on Croft Bridge was 84-5 feet above Ordnance Datum (Liverpool). Readings of the water level were commenced on 10th April, 1929, and continued during the whole period of observations in the tidal estuary. Readings were regularly taken twice daily—at 0745 and 1745 G.M.T. Current observations over the measured distance were taken at intervals and a cross- section of the river (Plate 2) was made near the centre of the measured distance to enable the necessary calculations of volume to be made. The observations at Croft Bridge served a twofold purpose. They provided data for estimating the volume of fresh water entering the tidal portion of the river. They also provided information on the passage of fresh water floods down the river so that, when exceptional conditions prevailed which would vitiate the results of current observations in the tidal estuary, the work in the estuary could be temporarily suspended until the flow of fresh water again assumed normal proportions. It has not been considered necessary to include the records of the water level at Croft Bridge in this report, as these observations are still in progress, The summer of 1929 was very dry and the river was at an exceptionally low level for long periods, on occasions falling to 3 in. on the gauge at Croft Bridge. The normal summer level was estimated to be 1 ft. on the gauge. During November and December, with heavy rainfall, the water level fluctuated considerably. On 10th November and 29th December the level rose to 16 ft. on the gauge. The alteration of level during heavy floods is very rapid. On 10th November the gauge read 15 ft. 6 in. at 0745, but at noon on the same day the level had fallen to 6 ft. On 11th December the river rose 8 ft. in 10 hours. The level appears to change more rapidly when the river is falling. On 24th October a flood passed Barnard Castle at 0400, reached Croft Bridge at 0900, and Yarm at 1415 on the same day. The highest reading recorded at Croft Bridge on this occasion was 8 ft. at 1700. The distance from Barnard Castle to Yarm by river is about 46 miles, which gives an average speed of about 44 miles per hour. During the winter months the level fluctuates considerably when the gauge reads above 2 ft., but after a few fine days without much rain the level remains fairly steady at 1 ft. 9 in. This height may be taken as the normal winter level. Local rain in Lower Teesdale does not appear to affect the height of the river appreciably. Owing to the narrow catchment area and the few tributaries, the fresh water floods can be definitely referred to heavy rain storms in Upper Teesdale. The only large tributaries draining the lowland are the Skerne and Leven, and floods in these tributaries are not heavy enough to affect the discharge of the Tees to any great extent. Above Piercebridge all the tributaries drain the hills in Upper Teesdale, and the water carried down by these tributaries adds appre- ciably to the discharge of the main river. In fine weather the river settles down with remarkable rapidity to the normal summer or winter level. It will, therefore, be seen that the/discharge of the river is only temporarily affected by heavy rain.
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