Exelon presentation oct 2011 bathymetry study

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Exelon presentation oct 2011 bathymetry study

  1. 1. Conowingo Hydroelectric Project (FERC No. 405) Sediment Task Force Meeting January 23, 2012 Marjorie L. Zeff, PhD., PG (URS) Gary Lemay (Gomez & Sullivan)
  2. 2. CONOWINGO POND BATHYMETRIC SURVEY  SURVEY OBJECTIVES  Create a thorough bed elevation map of Conowingo Pond  Determine where and to what extent Conowingo Pond’s sediment/bathymetric profile has changed since the 2008 USGS survey  Establish a physical “baseline” benchmark to better inform future sediment management decisions  WORK CONDUCTED  Collected bathymetric and water velocity data in Conowingo Pond  Week of October 24, 2011 (< 6 weeks after flows receded from Tropical Storm Lee)  26 previously surveyed USGS transect locations  33 additional transects, 5 longitudinal profiles  Conducted QAQC on collected data  Plotted 2011 data against 2008 data for each transect  Calculated and compared 2008 vs. 2011 average depths, sediment volume/load  Provided data (along with other sources) to USACE for use in the sediment model 2
  3. 3. 2011 Transect Layout 3
  4. 4. CONOWINGO POND BATHYMETRIC SURVEY  FINDINGS  USGS XC 19 and upstream are likely in dynamic equilibrium  Some areas of deposition and scour, but generally balanced  In the lower Pond (USGS XC 20 and below), deposition outweighed scour  Average cross-section depths generally decreased by 1 foot to 3.5 feet  Deposition occurred around banks/edges, scour in the main channel  The river thalweg appeared to shift toward the dam’s spillway in the farthest downstream cross-sections  Conowingo Pond accumulated approximately 5,870 acre-ft of sediment between the 2008 survey (fall 2008) and 2011 survey (late October 2011)  Net sediment deposition between the 2008 and 2011 surveys was 8.67 million tons, which translates to approximately 2.9 million tons of deposition per year  For reference, historic deposition rates have ranged from 3.1 million tons/yr from 1929-1958, to 2.5 million tons/yr from 1958-1993, to 1.5 million tons/yr from 1996-2008 (Langland 2009) 4
  5. 5. Upper Pond 110 2008-2011 Cross-Section Comparison - Looking Downstream 100Bed Elevation (ft NGVD 1929) 90 80 70 60 50 Data:GSE 2011. GSE XC3,USGS XC2 Data:USGS 2008. GSE XC3,USGS XC2 40 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 Distance from Left [West] Bank (ft) 5
  6. 6. Middle Pond 110 2008-2011 Cross-Section Comparison - Looking Downstream 100Bed Elevation (ft NGVD 1929) 90 80 70 60 50 Data:GSE 2011. GSE XC31,USGS XC15 Data:USGS 2008. GSE XC31,USGS XC15 40 0 1,000 2,000 3,000 4,000 5,000 6,000 Distance from Left [West] Bank (ft) 6
  7. 7. Lower Pond 110 2008-2011 Cross-Section Comparison - Looking Downstream 100Bed Elevation (ft NGVD 1929) 90 80 70 60 50 Data:GSE 2011. GSE XC41,USGS XC20 Data:USGS 2008. GSE XC41,USGS XC20 40 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 Distance from Left [West] Bank (ft) 7
  8. 8. Channel Shift Close to Dam 110 2008-2011 Cross-Section Comparison - Looking Downstream 100Bed Elevation (ft NGVD 1929) 90 80 70 60 50 Data:GSE 2011. GSE XC51,USGS XC25 Data:USGS 2008. GSE XC51,USGS XC25 40 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 Distance from Left [West] Bank (ft) 8
  9. 9. Longitudinal Profile 9
  10. 10. Questions? 10
  11. 11. Longitudinal Profile Differences 11

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