Sedimentation and Sediment Quality in SUDS Ponds
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Transcript of Sedimentation and Sediment Quality in SUDS Ponds
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
Retention Ponds
Falkirk Stadium Retention Pond (Undeveloped catchment)
Retention Ponds
Lidl Distribution Centre, Livingston - Retention Pond (Loading bay, Carpark runoff)
Physical Sedimentation Processes
InflowOutflow
Precipitation Evaporation
Advection and Diffusion
Deposition
Morphological Feedback
Flocculation
Infiltration
Sediment Accumulation
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 0.02 m a-1
MorphologicalDevelopment
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)
Morphological Evidence
Fan Development
Sediment Quality
What are the processes controlling the depositional fate of contaminants in ponds?
Need to examine: Sources Transportation/conveyance processes Depositional processes
Land-Use & Contamination
Vehicles Pavement Surface Debris
Brakes Tyres Frame & Body
Fuels & Oils
Concrete Asphalt De-icing Salts
Litter
Cadmium (Cd)
Chromium (Cr)
Copper (Cu)
Iron (Fe)
Lead (Pb)
Nickel (Ni)
Vanadium (V)
Zinc (Zn)
Chlorides
Organic Solids
Inorganic Solids
PAHs
Phenols
(Beasley and Kneale, 2002)
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.
Conce
ntr
ation (
mic
rogra
ms/
gra
m)
ZnNiPbCuCrCd
80
70
60
50
40
30
20
10
0
Interval Plot of Cd, Cr, Cu, Pb, Ni, ZnBars are One Standard Error from the Mean
Metals in Retention Pond Sediments
Metals in Retention Pond Sediments
Concentrations in Inlet/Outlet deposits show no consistent relationship
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Cd Cr Cu Pb Ni Zn
Metal
Conc
entra
tion
(mic
rogr
ams/
gram
)
Inlet Inlet Outlet
0
5
10
15
20
25
Cd Cr Cu Pb Ni Zn
Metal
Conc
entra
tion
(micr
ogra
ms/g
ram
)
Inlet (EF1) Outlet (EF3)
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. 137Cs 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