Susquehanna River Delivery of Sediments, History and Patterns

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Susquehanna River Delivery of
Sediments, History and Patterns

• Michael Langland
• U.S. Geological Survey
• Water Resources Division

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Discussion Topics

• Changes in River Flows
• Depositional Characteristics/Patterns
• Trapping Efficiencies
• Potential Impacts to the BAY

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Lower Susquehanna River Basin
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Susquehanna River Sediment Transport and Budget
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Susquehanna Sediment Transport

• Obvious relation to flow
• Approximately 3.1 MT sediment transported to
  Reservoirs, Long-term trapping ratio approx 55
• 25 of sediment load is delivered below
  Harrisburg (12 of basin)
• Ratio has changed over time

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Sediment Storage Capacity Conowingo Reservoir
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Sediment Loads for all RI Stations
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Susquehanna River Floods

• Period 1900-1999 (at Harrisburg)
• - Flood stage 17 ft 320,000 cfs 3-4 yrs
• - 28 floods since 1900
• - 100 yr flood 740,000 cfs 1972 and 1936
• Period 1900-1999 (Reservoirs)
• - 380,000 - 400,000 cfs needed to scour
• - 14 flow events gt scour threshold

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Wendy McPherson USGS - 9/20/04
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Susquehanna River
Bay Bridge
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Types of Flow Events

• Frequent events 1 or 2 yr
• - Bank Full Discharge (250,000 cfs)
• Episodic events 5-10 yrs
• - moderate amount of scour (380-600,000
• cfs)
• Catastrophic events 50 or 100 year floods
• - greatest amount of scour, load, and
  enviromental damage (gt600,000 cfs)

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Sediment Transport (Wolman and Miller 1960)

• 90 of the sediment is transported in flows that
  occur once every 5 years or less
• Greatest part of the sediment removed from the
  basin during the POR was carried by moderate
  flows not by catastrophic floods
• Analysis based upon Eastern US streams, Western
  US streams opposite

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Susquehanna Sediment Transport (at
Harrisburg)

• Period 1900-1999
• - Sed load from 20 largest flows 75 M tons
• - Sed load next 80 largest flows 70 M tons
• - Intervening high flows (2-3/yr) 100 M tons
• - Base flow
  75 M tons
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  Total 320 M tons

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Susquehanna Sediment Budget

• Period 1900-1999 (at Harrisburg)
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  Total 320 M tons
• Period 1900-1999 (to Reservoirs)
• Total 700 M tons
• Period 1930-1999 (trapped in Reservoirs)
• Total 300 M tons
• Period 1930-1999 (scoured in Reservoirs)
• Total 65 M tons

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Estimated Sediment Load to Reservoirs 1900-2000
120
100
80
Sediment Load (millions of tons)
60
40
20
0
Year
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Flow Events

• Catastrophic events short term, greatest
  sediment load and scour, greatest environmental
  damage
• Episodic events - long term, greatest sediment
  load and scour, lesser environmental damage
• Continue and increase stream restoration and
  monitoring efforts

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Sediment Storage Capacity Conowingo Reservoir
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Sediment Storage Capacity Conowingo Reservoir
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Catastrophic and Episodic Scour Events

• Above 400,000 cfs needed to scour
• 1972 (20 M), 1975 (3 M), 1996 (10 M)
• Approximately 33 M tons of sediment scoured
• About 42 M tons remain

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Predicted Sediment Scour vs. Flow
30.0
Scour estimates
95th percentile
95th percentile
25.0
Expon. (Scour estimates)
1972
1972
20.0
15.0
tons)
Predicted scour (millions of
1996
10.0
2004
1996
5.0
1975
1975
0.0
300
400
500
600
700
800
900
1,000
1,100
1,200
Instantaneous Flow (times 1,000)
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Total Deposition in the Reservoirs

• Constituent Safe
  Total
• (tons) Harbor Holtwold
  Conowingo (1990)
• Ammonia 34 k 2.2 k
  63 k 100 k
• Organic N 310 k 35 k
  470 k 815 k
• Phosphorus 75 k 8 k
  140 k 220 k
• Sediment 90 M 14 M 155
  M 250 M
• Iron 1.5 M 220 k
  3.5 M 5 M
• Aluminum 545 k 100 k 1.5
  M 2.1M
• Manganese 140 k 12 k 250
  k 400 k
• Coal () 10 15
  6 --

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When will the Reservoirs fill

• Predictions after 1996 at steady state no
  change in transport, scour, trap efficiency
• - 17 to 20 years
• Revisions in 2001 with changes in transport,
  scour, trap efficiency
• - 20 to 30 years
• Predictions (2004) with future changes
• - Ivan added 1.5 to 2 years
• - 20 to 25 years

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Implications when Reservoirs fill

• Loads entering will approximate loads leaving
• - Sediment 200-250 increase
• - Total phosphorus 30-40 increase
• - Total Nitrogen 2 increase

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Summary

• Decrease in sediment transport rates from
  watershed into the Reservoirs
• Distinct spatial change in sediment sources
• Reservoirs continue to fill and may reach SSC in
  20-25 years
• Delivery of sediment and any associated
  contaminants to the BAY will increase at SSC

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• Thank You

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• Thank You

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