Management of the Lower River Tame

Hannah Heng
School of Civil Engineering, University of Birmingham

Introduction

Urban rivers throughout the world have undergone degradation due to pollution and flood defence works. It is now recognized that this is unacceptable and rehabilitation is necessary. The West Midlands River Tame is an excellent study site having heavily impacted reaches and some restored reaches. The University of Birmingham is undertaking a major Natural Environment Research Council (NERC) study of the river as a contribution to the Urban ReGeneration of the ENvironmenT (URGENT) thematic research program. The study of the management of the Lower River Tame is, among one of the many contribution towards this program.

Objectives

• To identify the sources and sinks of pollution at the Lower Tame.

• To investigate how the river response to forcing functions such as pollution load inputs and flow.

• To understand the kinetics of the Lower River Tame.

• To predict changes of water quality in the river for various rehabilitation strategies.

Study Area

Methodology

This research project involves analyzing existing water quality and flow data obtained from monitoring stations along the Lower Tame. In addition, the utilization of a stochastic computer modelling that calculates the river water quality throughout a catchment called SIMCAT is involved. Sampling and other fieldwork is undertaken in order to facilitate the validation of these modelling results.

Results & Discussions

The Environment Agency has strategic chemical water quality targets for all rivers. River Tame mostly fails due to high ammonia and BOD (Biological Oxygen Demand) level and ammonia is thus, discussed in greater depth and detail.

Sources & Sinks of Pollution Load

From Fig.2, the main ammonia load input into Lower Tame is accounted to Minworth HT due to poor performance of Minworth STW during 1993-96. It has since been improved and hence, causing significant improvement in water quality (see Fig.4). Although Lea Marston purification Lakes is efficient in removing BOD loads, diffusion of ammonia from the bed causes a significant ammonia increase in the Lower Tame.

River Response to Pollution Load

From Fig. 3, in the first 10km downstream from Water Orton, the discharge of treated effluent from STW causes an increase in ammonia level. Approaching the lakes, further increase of ammonia is observed due to ammonia diffusion from its bed. Since tributaries such as River Cole also contribute ammonia loads into the river and flow is small, no significant dilution or self-purification of the river is observed.

Beyond the lakes, there is a massive recovery of ammonia, reducing the ammonia level from 2.5 to 0.8 mg/l. This optimistic response is slightly puzzling because to produce such a massive recovery, the decay rate of ammonia would be unrealistically high (roughly about 10 times the average value).

Algae in Ammonia Uptake

A preliminary hypothesis to explain the massive ammonia recovery observed beyond the lakes is that algae are taking up the ammonia. Algae are photoautotrophic organism commonly found in rivers, either living at the riverbed as benthic algae or suspended in the water column. It needs nutrients such as ammonia and phosphorus for growth and reproduction. Assuming that the hypothesis is true, estimation of alga concentration is needed to determine if the amount is reasonable. To find out the concentration of algae in the Lower Tame through fieldwork sampling and laboratory test would be time consuming. A preliminary estimation of alga concentration is thus calculated based on the U.S Environment Protection Agency guide. From this, alga concentration of roughly about 300 mg/l is obtained, which is the value one would expect from an urban river. However, more research needs to be done for conclusive results.

Predicting Changes of Water Quality

In 1998-1999, major work has been undertaken to improve the performance of STW, especially at Minworth HT under the water industry’s agreed capital investment programme (AMP 2). The effects of this in terms of water quality improvements are predicted. From Fig.4, with reduced impact from the STWs, the ammonia level along Lower Tame is reduced, particularly at river stretches before approaching the lakes. The response of Lower Tame remained the same, with the lakes still generating ammonia.

Conclusions & Future Work

• An initial understanding of the kinetics and sources/sinks of pollution at Lower Tame.

• Predictions of water quality due to future improvements are strongly dependent on Water Orton.

• More conclusive results of the role of algae in ammonia uptake at Lower Tame need to be found.

• SIMCAT modelling need to be extended to the Upper Tame, together with obtaining a better understanding of its kinetics.

• GIS will be used to incorporate existing knowledge and the model results, and will provide an input to the Decision Support System, which will aid the evaluation of rehabilitation strategies.