CHARACTERISATION OF HARTBEESPOORT DAM SEDIMENT BODY by gyvwpsjkko

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									      CHARACTERISATION  OF 
HARTBEESPOORT  DAM SEDIMENT BODY
             HBP Dam Remediation

Reduction of Internal Nutrient Load (focus on
Phosphorous) - one of Goals of HBP Dam
remediation and abatement Dam Eutrophication
        Internal P Load (roughly estimated)
                   120 to 150 tP/a
Causes:
•The release of P trapped in active sediment layer
•Cycling of P among Sediments, Water & Biota
NEED TO STUDY DAM SEDIMENT BODY

• Characterise the Active Sediment Layer
• Provide elements for potential Dredging
• Consider potential for Beneficiary uses
• Provide elements for ;
  - Environmental Risk Analyses
  - Cost - Benefit Analyses
        STUDY OF SEDIMENT BODY
• Data Collection & Analyses
•   Historical Data (DWAF; 1923, 1970, 1990)
•   Data on contours measurements (DWAF, 2007/2008)
•   Other relevant data
• Modeling & Calculations
•   3D model of Sediment Body ( MatLab Environment )
•   Sediment spatial distribution analyses
•   Volumes Calculations
• Sediments Characterisation
•   Sampling
•   Lab Analyses
• Analyses & Quantification
MAPPING OF HARTBEESPOORT DAM BOTTOM
 Key lateral sediment sections surveyed (DWAF 2007/08)
Dam’s Sediment Contours
  Section 5 contour (Dam Wall zone)
Illustration compiled from DWAF data and field measurements
    Dam Sediment Body Modeling
Inputs:
• Data Sourcing
• Data consistency check
• Computer Program in MatLab Environment
• Linear interpolation  (min. 200 segments each cross section)

Outputs:
• 3D Contours and Shaded Plots
• Spatial Distribution Analyses
• Volume Calculations
Shaded Plot of Bottom Contours




   1923




                       2008
Sediment Longitudinal Profile
  ( lowest edge points in Main Basin )
SEDIMENT DISTRIBUTION & ZONING
     DATA on HBP DAM ( 2007/08 )

• Area ( to FSL* )               2060 ha

• Tot. Volume ( to FSL* ) 205 - 215 x 106 m3
• Sediment Volume                35.25 - 41.25 x 106 m3

• Exhausted Dam Volume 16.4 - 20.1 %
• Dam Live Storage                164 - 179 x 106 m3


* Full Supply Level - 1162.34 m asl
                SEDIMENT VOLUMES (Total)

                         Total Area   Area covered by     Total Volume of     Total Volume of
         ZONE                                                             3
                            (ha)      sediments (ha)    sediments (000 m )     ASL* (000 m3)

Dam Wall                    150           45 - 55         5 250 - 6 750         450 - 550

Main Basin                 1060          350 - 450       28 000 - 32 000       3 500 - 4 500
(Crocodile Mouth)        (50 - 60)       (30 - 35)         (2.25 - 2.75)        (300 - 350)

Megalies Basin              850           55 - 60         2 000 - 2 500         550 - 600
(Megalies Mouth)            (50)         (35 - 40)        (1 500 - 1 800)       (350 - 450)

TOTALS                     2 060         525 - 655       35 250 - 41 250       4 500 - 5 650

‘Jelly” Layer             60 - 70                         1 000 - 1 500            N/A

* ASL - Active Sediment Layer
Crocodile River Bed (BWS) and Mouth
Crocodile river Sediment Contours
  Crocodile River Bed (BWZ*) and Mouth

River Mouth:
• Area                 ~ 45 - 55 ha
• Tot. Volume (to FSL) ~ 5.5 – 6.1 x 106 m3
• Sediment Volume      ~ 2.25 - 2.75 x 106 m3 (~ 43%V)
Backwater zone:
• Area                 ~ 40 ha
• Tot. Volume (to FSL) ~ 3.57 x 106 m3
• Sediment Volume      ~ 1.7 - 2.2 x 106 m3 (~ 59%V)
* BWZ - Backwater Zone
SEDIMENTS CHARACTERISTICS


• Sediment Sampling (cores 1.5 m)
• Lab Analyses (slices 0.5 m)
• Data Analyses
SAMPLING POINTS
SAMPLING EQUIPMENT
Sediment Samples
                      LAB ANALYSES
• General parameters; pH, EC, Dry solids, Density, COD
• Plain Nutrients;            N Forms, P forms, Carbon
• Specials;                   Oil & Grease, Surfactants
• Anions;                     Sulphate, Chloride, N Species, Sulphide, etc.
• Cations: Ca, Mg, K, Na, Si, Fe, Mn, B, Se, Al, Cu, Zn, Ni, As, Cd, Hg…
• Gross β radioactivity
• Organic compounds:         VOHs, Phenols, ChlorPhenoles, PAHs, EOX,
  Chlorbenzenes, PCBs, Cl-Pesticides, P-Pesticides, N-Pesticides, Phtalates,

• Bio-Agents:                 Helminth Ova, HPC, Tot. Coli, E. Coli
       Sediments Characteristics
                       ( Cores ~ 1.5 m )

• Dry solids 25% - 55% (mostly 30 - 35%)
• Density * ( 1.18 - 1.45 t/m3)
• P content ( 0.45 - 0.95 gP / kg DS)
• N content ( 2 - 4 gN / kg DS)
• C content ( 30 - 45 gC / kg DS)
*   Jelly Layer density - 1.11 t/m3
Note: Significant difference between sediments in Megalies basin and Main
  basin
         CONCENTRATION STRATIFICATION
     
                                                     ( Section 5 )
         50                                                            50
                Dry solids (%)                                               Carbon (g/kgDS)

         40                                                            40


         30                                                            30


         20                                                            20


         10                                                            10


           0                                                           0.0
                  0.0 - 0.5        0.5 - 1.0   1.0 - 1.5   Depth (m)          0.0 - 0.5     0.5 - 1.0   1.0 - 1.5   Depth (m)
         1.2
                                                                       4.0
               Total P (g/kgDS)
                                                                             Organic N (g/kgDS)
         1.0

                                                                       3.0
        0.80


        0.60
                                                                       2.0

        0.40

                                                                       1.0
        0.20


         0.0
                 0.0 - 0.5        0.5 - 1.0    1.0 - 1.5   Depth (m)   0.0
                                                                              0.0 - 0.5     0.5 - 1.0   1.0 - 1.5   Depth (m)
          Sediment Characteristics
                           ( Cores ~ 1.5 m )

•    Low to moderate salinity
•    No toxic inorganic species over MPL
•    No organic compounds over MPL *
•    No helminth ova detected
•    Bacterial count in the acceptable range
• Low β radioactivity
Notes:
 Code A1a (RSA Guidelines for the utilization and disposal of wastewater sludge)
*   US EPA Sediment Quality Guidelines
MAJOR COMPONENTS TRAPPED IN SEDIMENTS
                   ( Total )


 Dry Solids    ~ 14 500 000 - 17 000 000 t
 Nitrogen      ~       20 000 - 35 000 tN
 Phosphorous   ~        4 600 - 5 200 tP
 Org. Carbon   ~      150 000 - 250 000 tC
          Major components
  trapped in Active Layer * Sediments


Dry Solids             ~ 1 650 000 - 2 000 000 t
Nitrogen               ~     4 950 - 5 850 tN
Phosphorous            ~      1 050 - 1 250 tP
Org. Carbon            ~    49 500 - 58 500 tC
* Active Layer ~ 1 m
                 “JELLY” LAYER
           a Huge Natural Bio-Reactor

• Discovered in Dam Wall Zone
• Rich in Organics and Nutrients
• Composed of fine clay particles and Detritus
• Continuously receives dead biomass
• Bio-reactor driven by Biodegradable Organic Carbon
• N & C transforms to inorganic and gaseous products,
• Liberates P incorporated in dead tissues
• Intensive exchange of matter with overlaying water
         MAJOR COMPONENTS
        contained in “Jelly” Layer


Dry Solids     ~ 166 000 - 277 000 t
Nitrogen       ~     565 – 780 tN
Phosphorous    ~      35 - 49 tP
Org. Carbon    ~    10 400 - 14 500 tC
Estimate Phosphate Balance
   SEDIMENTS CHARACTERISTICS
                ( Cores ~ 1.5 m )




    Resource not a Waste
• Harmful for an Aquatic Environment
• Beneficial for a Terrestrial Environment

								
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