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