Presentation on theme: "Sedimentation and Sediment Quality in SUDS Ponds Alan J Jones Industrial CASE PhD Studentship Funded by:"— Presentation transcript:
Sedimentation and Sediment Quality in SUDS Ponds Alan J Jones Industrial CASE PhD Studentship Funded by:
Overview 1.Background Context 2.Physical sedimentation & geomorphology in Retention Ponds 3.Geochemical processes & contamination in Retention Ponds 4.Aims & direction of research
Justification Excessive build-up of sediment in Retention Ponds – reduction in flow attenuation capacity Water residence time reduced – less time for settling of suspended sediments and contaminants Need to establish maintenance costs: Frequency of excavation Volumes of sediment involved Quality of excavated sediments Route of disposal Permeable substrate – leaching of contaminants into aquifers – contamination of potable water
Retention Ponds Flow attenuation of retention ponds is well- characterised: lumped modelling (Wallis et al., In press) Research into sedimentation: Field-based sampling (numerous studies) Flume-based transportation modelling (Krishnappan and Marsalek, 2002) Computational fluid dynamics (CFD) modelling of storage tanks (Adamsson et al., 2003) But need to understand sedimentological effects on the long-term performance of ponds
Sedimentation in Retention Ponds Rates in ponds are generally low: Highly variable spatially and temporally, and depends upon several factors: Climate Land-use Grain size Basin design Position in treatment-train Yousef et al. (1994)Striegl (1987)Marsalek et al. (1997) 0.00783 m a -1 0.02 m a -1 Morphological Development
Morphological Conditioning? Research into channel confluences has shown that form and process cannot be easily separated (Lane, 1998) Reflexive and reciprocal nature – positive feedback In less dynamic structures, such as retention ponds, is this concept tenable?
Hypothesis: Flow short- circuiting Flow short circuiting is demonstrated in the literature (Marsalek et al., 1997) and known to occur in retention ponds in Scotland (Stenton Pond, Glenrothes) Does this exacerbate morphological conditioning? Is this based purely on the inlet/outlet configuration or does pond-design (i.e. initial morphological state) promote or inhibit flow-short circuiting? What structures develop as retention ponds age?
Morphological Evidence Plunge pool / Scour Zone Bar Deposits Graded Deposits (Coarse – Fine)
Heavy Metal-Sediment Dynamics No obvious signature for heavy metals and land-use As metals are transported from source to deposit – variety of processes occur: Partitioning Metal Speciation Adsorption Complexation Precipitation Extraneous influence of local lithology (Vicente- Beckett, 1992) and seasonality (Mungur et al., 1995)
Metals in Retention Pond Sediments Literature review – Pond data Examined ponds in Sweden, Florida, Oregon, North Carolina, Ontario, Dunfermline and Edinburgh. Aggregate of the data shows: No association between 6 metals studied Zinc (Zn) has the largest range of values, Cadmium (Cd) the smallest.
Concentrations in Inlet/Outlet deposits show no consistent relationship Echo Farms Pond, Wilmington, North Carolina (Mallin et al., 2002) Vallby, Vasteras, Central Sweden (Färm, 2002) Increase in concentration from Inlet to Outlet Decrease in concentration from Inlet to Outlet
Sediment Quality Issues Need to understand the relationships and relative importance of metal-sediment interactions: For source-to-deposit transportation and Depositional fate in retention ponds Can these processes be modelled for individual ponds? Look further at tracing techniques since fingerprinting techniques (e.g. 137 Cs and mineral magnetics) have proven ineffective (Charlesworth et al., 2000)
Research Questions 1.What processes control the spatial and temporal distribution of sediments within retention ponds? heavy metals within retention ponds? 2.Which morphological structures develop over time within retention ponds? 3.To what extent does morphological feedback control the hydrodynamics of the retention pond? 4.Do these morphologies affect the capability of the pond to attenuate flow and capture sediment? 5.Does any relationship exist between emergent morphological structures and the depositional fate of heavy metals? 6.How can this information be used to inform remedial practices such as the dredging of sediments? 7.What are the cost-effective and environmentally friendly disposal routes for excavated SUDS sediments?
Current Work: Method Development Scoping study of Retention Ponds in Scotland: 22 sites visited in the last few weeks Assess the suitability of GPR for constructing a high resolution DEM of pond bathymetry: In conjunction with core samples, reconstruct depositional history of the basin Examine tracing techniques: Provenance of sediment Influence of land-use on pond sediment geochemistry Review existing modelling capabilities: Computational modelling/CFD Simulation of different initial pond designs Simulate dispersal of heavy metals