Exelon presentation oct 2011 bathymetry study

Conowingo Hydroelectric Project (FERC No. 405) Sediment Task Force Meeting January 23, 2012 Marjorie L. Zeff, PhD., PG (URS) Gary Lemay (Gomez & Sullivan)

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

2011 Transect Layout 3

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

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

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

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

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

Longitudinal Profile 9

Questions? 10

Longitudinal Profile Differences 11

Exelon presentation oct 2011 bathymetry study

by Stewards of the Lower Susquehanna on Jan 28, 2012

Accessibility

Categories

Tags

Upload Details

Usage Rights

Statistics

Exelon presentation oct 2011 bathymetry study — Presentation Transcript