The East Kent Chalk Aquifer during the 1988-92 Drought

Groundwater resources of Chalk aquifers may become depleted during drought periods; major causes of this depletion include reductions in the aquifer transmissivity and the interaction between aquifers and rivers. In the East Kent aquifer there are certain catchments where difficulties are encountered in maintaining yields but, in other catchments, drought periods have little effect on the available resources. A mathematical model is developed to help understand the flow processes within the aquifer system, and the model is used to predict the consequences of possible abstraction scenarios.     

Groundwater Model of Conditions in Liverpool Sandstone Aquifer

T his study considers the groundwater conditions for the period 1948–82 in the Permo-Triassic Sandstone aquifer of the Liverpool area. During this period, significant changes have occurred in the abstraction patterns and a new railway tunnel has been constructed below sea level in Central Liverpool. To understand the flow conditions within the aquifer, detailed studies have been carried out into the aquifer properties, the influence of rivers and tunnels, and the estimation of recharge. It is found that conventional rainfall recharge accounts for only one-third of the total recharge.
Numerical model solutions were used to check the adequacy of the understanding of the flow processes and the solutions have confirmed that the rising water levels in Central Liverpool result from high recharge and a reduction in abstraction. Having validated the model by comparisons with field data, the model was then used to predict the probable future water level changes.     

Sludge Bulking Control with Ozone

O zonation was studied as a non-specific means of sludge bulking control. Direct ozonation at 6 g/m³ influent, i.e. 4 gO₃/kg sludge per day into the aeration basin of a 150 l/d Phoredox system controlled the growth of filamentous organisms and improved the settleability of the sludge. Bulking control with ozone is not significantly more expensive than with chlorine or with larger settler capacity.     

NATURAL SEWAGE TREATMENT IN THE UK: SELECTION GUIDELINES

The design of septic tanks, constructed wetlands, waste-stabilisation ponds and rock filters is detailed, and their applicability in the UK is discussed. Septic tanks are a suitable primary treatment system for villages with a population of less than 500. Constructed wetlands, which are secondary or tertiary treatment units, have the disadvantage that their plants do not play any significant role in their performance, except for nitrogen removal. Secondary facultative waste-stabilisation ponds, with pre-treatment in septic tanks and post-treatment in rock filters, provide primary, secondary and tertiary treatment and can produce high-quality effluents. The costs of these processes for small rural communities in the UK are compared.     

ESTIMATING RECHARGE FOR BRITISH AQUIFERS

This paper reviews methods of estimating recharge for a wide variety of aquifers in Britain. A soil moisture balance technique is used with direct representation of relevant soil and crop properties. Recharge contributions due to rainfall, runoff from impervious areas and leaking water mains and sewers are considered. In many field situations low permeability strata, which overlie the main aquifer, modify the timing and magnitude of the actual recharge. Runoff from less permeable strata can become runoff-recharge at the aquifer outcrop. Reference is made to several case studies.     

Post-Implementation Appraisal of a Two-Stage Channel in the River Roding, Essex

T he performance of a two-stage river channel is examined from a combination of collected field data on the River Roding and a hydraulic model study. Particular attention is paid to the vegetation on the upper channel berm, including its seasonal effect on hydraulic resistance and the problem of channel maintenance. Recommendations are made with respect to (a) increasing the present capacity of the River Roding, and (b) the future design of two-stage flood channels intended to meet stringent environmental standards.     

The Reliability of Groundwater Sources to Meet Increasing Demands

The groundwater resources of the Lee Valley Water Company have been examined in a joint study with the University of Birmingham. The Company is modifying its operating policy to make maximum use of the groundwater resources, which has involved the development of new methods of estimating the reliable output of the groundwater sources under differing conditions. The technology transfer involved in the project has enabled the Company to gain a greater understanding of the operation of its sources, and the University has modified existing techniques so that they are of greater practical use.     

The Effect of Borehole Sealing on the Southern Lincolnshire Limestone Catchment

The Southern Lincolnshire Limestone is an important groundwater resource; however, for many years water has been lost from the aquifer system through uncontrolled artesian flow from wild-bores in the Fenland area. During 1991–92, there was an extensive programme of sealing or controlling the wild-bores, and compensation flows for ecological and farming purposes were provided at some sites.
This paper describes a field study which was designed to identify the important features of part of the catchment; this was followed by the development of an existing groundwater model to provide an improved representation of the uncontrolled and controlled wild-bores. The model is used to assess the consequences of controlling or sealing the wild-bores.     

The Effect of Overbank Flow in a Meandering River on its Conveyance and the Transport of Graded Sediments

A large-scale model hydraulic study of inbank and over-bank river flow, using a regular sinuous river channel with a mobile bed, was carried out in the Flood Channel Facility at HR Wallingford, UK. The selected sediment had a wide range of particle sizes present over the 'fine sand to coarse sand'range. Flow velocity, local and global sediment transport rates, and channel conveyance were all measured. The resulting bed forms were determined and used to explain the secondary circulation in the sinuous channel as well as the size sorting of the sediment. The paper gives an early overview of this major project.