『Abstract
Groundwater-river exchanges in an urban setting have been investigated
through long term field monitoring and detailed modelling of a
7 km reach of the Tame river as it traverses the unconfined Traiassic
Sandstone aquifer that lies beneath the City of Birmingham, UK.
Field investigations and numerical modelling have been completed
at a range of spatial and temporal scales from the metre to the
kilometre scale and from event (hourly) to multi-annual time scales.
The objective has been to quantify the spatial and temporal flow
distributions governing mixing processes at the aquifer-river
interface that can affect the chemical activity in the hyporheic
zone of this urbanised river. The hyporheic zone is defined to
be the zone of physical mixing of river and aquifer water. The
results highlight the multi-scale controls that govern the fluid
exchange distrbutions that influence the thickness of the mixing
zone between urban rivers and groundwater and the patterns of
groundwater flow through the bed of the river. The morphologies
of the urban river bed and the adjacent river banj sediments are
found to be particularly influenced in developing the mixing zone
at the interface between river and groundwater. Pressure trasients
in the river are also found to exert an influence on velocity
distribution in the bed material. Areas of significant mixing
do not appear to be related to the areas of greatest groundwater
discharge and therefore this relationship requires further investigation
to quantify the actual remedial capacity of the physical hyporheic
zone.
Keywords: Urban; Groundwater; Hyporheic zone; Accretion; Modelling』
1. Introduction
2. Approach
3. The field setting and data collection
3.1. Hydrology
3.2. Hydrogeology
3.3. Field data collection
3.4. Field results: groundwater-surface water interactions
4. Modelling codes
5. Hypotheses, model development and results
5.1. Regional groundwater flows (Hypothesis 1)
5.1.1. Conceptual and numerical model
5.1.2. Discussion
5.2. Bank storage (Hypothesis 2)
5.2.1. Conceptual and numerical model
5.2.2. Discussion
5.3. River bed heterogeneity (Hypothesis 3)
5.3.1. Conceptual and numerical model
5.3.2. Discussion
5.4. Momentum exchange (Hypothesis 4)
5.4.1. Conceptual and numerical model
5.4.2. Discussion
6. concluding remarks
Acknowledgements
References