Sediment Behind The Dams Army Corps of Engineers


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Conowingo Dam presentation by Army Corps of Engineers, shown at the Choose Clean Water conference

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  • Recent funding to restart and scope study Issue of the long-term buildup of sediment behind the dams in the lower Susquehanna Implications of the Conowingo dam reaching steady state (filled to a level where sediment is no longer retained). History of Corps involvement Recent brainstorming for study approach Potential path forward
  • STF-charged with reviewing existing studies related to Susquehanna sediment transport and storage; evaluating management options; Recommending continued areas of study, research, or demonstration. Corps part of task force. 2001-Corps has authority to study sediment management measures 2002-specific funding for sediment management behind dams.
  • Corps involvement with this study From that original authority(2001)/funding(2002) the recon phase started Authority language was broad (shoreline erosion plus related sediment management) measures so Divided into two parts Pieces of recon phase approved received authorization/funding to proceed into feasibility-checked marked items Part I-Reservoir sed management & Sediment Transport did not proceed into feasibility.-talk about later Model worked on by Cerco and others updated Bay model with sediment components Part II both pieces proceed into feasibility draft Shoreline MGMT guide-draft report – prioritizes areas for further investigation; where living shorelines should be implemented. Technical guide-for contractors-”how-to” build living shorelines.
  • Background on Corps study process once authorization and funding is received. Traditional Study leads to construction; not all do (master plan). Talk about later.
  • Reservoir study was scoped as a traditional feasibility. Another (newer) option is a river basin assessment which we are looking to do with this study Studies can lead to a master plan- What can we do to reduce problem? Where should work be done? Variety of recommendations implemented by different entities.
  • For the Reservoir sediment management portion of the recon project PMP and cost-sharing negotiations were initiated in 2003, Difficulties in agreeing on the final scope and lack of funding has prevented further progress.
  • Restart study-looked into original recommendations 1. Dredging alternatives 2. Upland, riverine management recommendations. Conversations about the reservoir ended up being discussions on the watershed sediment.
  • Based on recommendations and discussion worked up this approach. Study wouldn’t lead to construction but instead would lead to development of a Sediment Management Plan Existing conditions in each of these areas risks, sediment grain size Includes options for the watershed and the reservoir itself We are open to alternatives
  • STAC workshop- was to survey possible consequences of increased sediment from the Susquehanna to bay because of loss of storage capacity behind dams. STAC could not predict timing or intensity of scouring events Emphasized the complexity of possible effects of more sediment or an increase in severe storms. More phosphorus-sediments will move beyond estuarine turbidity maximum zone. More flow=more sediments in channels More sediments=more light=SAV impacts More sediment –buried benthics more energy use More sediment-effects to fish feeding, smothered eggs, clogged gills, etc.
  • Conowingo is currently a huge BMP Langland, M.J., and Hainly, R.A., 1997, bathymetry study Regardless of whether dredging to extend the life of sediment storage capacity is undertaken, the Task Force concluded that reducing sediment loading throughout the basin is critical. Recommendations for sediment management, designed to improve BMPs in watershed to reduce sediment flow.
  • Complexity/unanswered questions. Questions that still remain Scope study-some things we could investigate. Larger sediments remained trapped while small silts/clays travel over the dam.
  • Discussion/Development Sediment Management plan approach Who can we cost share with Sediment TAsk force 10-29 Conference calls with ERDC SIAM model can tackle watershed sediment management. Evaluates multiple sediment management alternatives on a watershed scale. Compares computed annual transport capacity with bed material supply to determine sediment balance on a reach-by-reach basis. It can evaluate the impact of sediment reduction measures on channel equilibrium to identify potential problems. User must determine local sediment source contribution and composition Output: local balance (bed material minus transport capacity of a reach); avg annual transport capacity; bed material supply; wash material supply; local supply Tracks particles by sediment size. Sediment sources and sinks (all inputs to sediment load) For modeling sedimentation in the reservoir, we have several 1D and 2D models that would be suitable. flyash problems at the TVA reservoirs. How does reservoir behave? What happens when dam is removed, incised? Where do sediment deposit? How far do sediments travel?
  • Path forward to begin study next FY.
  • IF there is a signed agreement by September, study could start next year-IDEAL Due to the fact USACE-has limited funding in Recon phase to keep a study moving without a sponsor. If there is no interest once our funding is gone the study runs the risk of delays, cycle back to what happened with the study prior. In order to keep Congressional funding flowing, we have to show good progress
  • Sediment Behind The Dams Army Corps of Engineers

    1. 1. Sediment Behind the Dams Anna Compton USACE Baltimore District October 29, 2009
    2. 2. How the Corps Got Involved <ul><li>SRBC formed Sediment Task Force – July 1999 </li></ul><ul><ul><li>Symposium held – December 2000 </li></ul></ul><ul><ul><li>Recommendations released – June 2002 </li></ul></ul><ul><li>Corps given authority to study “shoreline erosion and related sediment management measures which could be undertaken to protect the water quality and land resources of the Chesapeake bay watershed” – May 2001 </li></ul><ul><li>Funding from Congress provided to “examine management measures that could be undertaken to address the sediment behind the dams on the Lower Susquehanna” – 2002 </li></ul>
    3. 3. Original Reconnaissance Phase <ul><li>Part I - Sediment Behind the Dams on the Lower Susquehanna River </li></ul><ul><ul><li>Reservoir Sediment Management </li></ul></ul><ul><ul><ul><li>Dredging/Beneficial use alternatives </li></ul></ul></ul><ul><ul><li>Susquehanna River Basin Sediment Transport </li></ul></ul><ul><ul><ul><li>Sediment Budget/basin-wide sediment management recommendations </li></ul></ul></ul><ul><ul><li>Chesapeake Bay Sediment Budget, Modeling, and Regional Sediment Management </li></ul></ul><ul><ul><ul><li>Updated sediment components of model to increase knowledge and capabilities surrounding sediment resuspension and shoreline erosion </li></ul></ul></ul><ul><li>Part II – Chesapeake Bay Shoreline Erosion </li></ul><ul><ul><li>Chesapeake Bay Shoreline Management Guide </li></ul></ul><ul><ul><li>Technical guide for shoreline protection </li></ul></ul>
    4. 4. USACE Process 101 <ul><li>Reconnaissance Phase </li></ul><ul><ul><li>Generate a small report to determine Federal Interest </li></ul></ul><ul><ul><li>Scope and Execute an Agreement </li></ul></ul><ul><li>Feasibility Phase </li></ul><ul><ul><ul><li>Detailed Analysis </li></ul></ul></ul><ul><ul><ul><li>Feasibility Report </li></ul></ul></ul><ul><li>Plans and Specification Phase </li></ul><ul><ul><li>Designs </li></ul></ul><ul><li>Construction Phase* </li></ul><ul><ul><li>Construct Project </li></ul></ul><ul><ul><li>*Traditional Study </li></ul></ul>
    5. 5. USACE Feasibility Phase 101 <ul><li>Traditional Feasibility Study (2003 Reservoir study) </li></ul><ul><ul><li>50 Federal/ 50 Non-Federal cost share </li></ul></ul><ul><ul><li>USACE recommendation for Implementation </li></ul></ul><ul><ul><li>Detailed Designs for Construction </li></ul></ul><ul><li>River Basin Assessment </li></ul><ul><ul><ul><li>75 Federal/25 Non-Federal </li></ul></ul></ul><ul><ul><ul><li>Basin System Analyses </li></ul></ul></ul><ul><ul><ul><li>Conceptual-level designs </li></ul></ul></ul><ul><ul><ul><li>Master Plan </li></ul></ul></ul>
    6. 6. Original Reconnaissance Phase Reservoir Sediment Management <ul><li>Fall 2003, SRBC and the Corps had scoped a cost-shared study estimated at $2 million </li></ul><ul><li>Primarily a dredging feasibility study </li></ul><ul><li>Options for use or disposal of dredged material would have been studied and compared </li></ul><ul><li>No Feasibility Cost Sharing Agreement (FCSA) was signed, study was not initiated </li></ul>
    7. 7. Feasibility Phase Brainstorming <ul><li>SRBC published Sediment Task Force </li></ul><ul><li>Recommendations, June 2002 </li></ul><ul><ul><li>“First, a feasibility study is recommended to determine if dredging the reservoirs is a viable option to maintain or reduce the volume of sediment currently trapped behind the dams. </li></ul></ul><ul><ul><li>Concluded that reducing sediment loading throughout the basin is critical.” </li></ul></ul>
    8. 8. Feasibility Phase Approach-Concept Lower Susquehanna Watershed Reservoirs Determine Existing Conditions, Problems, Future Risks Chesapeake Bay Lower Susquehanna River Sediment Management Plan Watershed Options BMP’s Impacts Costs Dredging Impacts Costs Reservoir Options Implementation Options Benefits Implementation Options Other Solutions? Who Can Help? Other Solutions? Who Can Help ? Benefits
    9. 9. Why a Sediment Management Plan? <ul><li>STAC Workshop The Impact of Susquehanna Sediments on the Chesapeake Bay , May 2000 </li></ul><ul><ul><li>“ Detailed predictions are therefore not possible but the consequences that can be predicted with the most confidence are: </li></ul></ul><ul><ul><li>Increased Phosphorus in Middle Bay </li></ul></ul><ul><ul><li>Increased need for dredging navigation channels in Upper Bay </li></ul></ul><ul><ul><li>Higher turbidity and faster sedimentation everywhere, but especially in the navigation channels </li></ul></ul><ul><ul><li>Adverse effects on recovery of SAV </li></ul></ul><ul><ul><li>Impacts to benthic organisms </li></ul></ul><ul><ul><li>Impacts to fish” </li></ul></ul>
    10. 10. Why a Sediment Management Plan? <ul><li>Conowingo stores nutrients </li></ul><ul><ul><li>670,000 tons of total nitrogen (9x annual load) </li></ul></ul><ul><ul><li>130,000 tons of total phosphorus (50x annual load) </li></ul></ul><ul><li>Conowingo currently traps: </li></ul><ul><ul><li>60%-70% of suspended sediment load </li></ul></ul><ul><ul><li>2% of total-nitrogen load </li></ul></ul><ul><ul><li>40% of total-phosphorus load </li></ul></ul><ul><li>If dam reaches steady state it is estimated that there will be average annual increases of: </li></ul><ul><ul><li>250% in suspended sediment load </li></ul></ul><ul><ul><li>2% in total-nitrogen load </li></ul></ul><ul><ul><li>70% in total-phosphorus load </li></ul></ul><ul><ul><li>Langland and Hainly, 1997 </li></ul></ul><ul><li>Current (2009) USGS estimates have the dam reaching steady state in 15-20 years (not including scour events) </li></ul><ul><ul><li>Langland 2009 </li></ul></ul>
    11. 11. Conowingo Dam and Reservoir Chesapeake Bay Susquehanna River Basin Nitrogen? Phosphorus? Sediment? What sediment is trapped? When does it move? What happens when it gets here? Where does the sediment come from? How far does sediment move past the dam? What sediment is not trapped? What could happen if the basin fills? Long Term: Can sediment stabilized in the watershed? Short Term: Can sediment storage be increased at the dam? How do the sediments/nutrients affect living resources in the Bay? How is it transported? How does sediment behave in the ETM? What would happen if there is a scouring event? Who can participate in a study?
    12. 12. Current Corps Activities <ul><li>Sediment Management Plan </li></ul><ul><ul><li>Looking for Cost-Sharing Partners (75/25) </li></ul></ul><ul><ul><li>Reconvene Sediment Task Force – OCT 29 TH </li></ul></ul><ul><ul><li>Outreach Discussions </li></ul></ul><ul><ul><ul><li>Engineering Research Development Center (ERDC) </li></ul></ul></ul><ul><ul><ul><ul><li>Sediment Impact Analysis Methods (SIAM) Model </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Application to Watershed Sediment Management Options </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Can evaluate sediment management alternatives on a watershed scale </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><li>2D Adaptive Hydraulics Model (ADH) </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Application to Reservoir Sediment Management Options </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Sediment transport/deposition </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><li>Chesapeake Bay Model </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Application to Chesapeake Bay Impacts </li></ul></ul></ul></ul></ul>
    13. 13. Path Forward <ul><li>Today - Sediment Task Force Meeting </li></ul><ul><ul><li>List of Recommendations/Study Priorities </li></ul></ul><ul><li>Secure Sponsor(s) </li></ul><ul><li>Finalize Scope Study/Sign Agreement </li></ul><ul><li>Start Feasibility Phase </li></ul>
    14. 14. Timeline <ul><li>Project Management Plan Outline – November 2009 </li></ul><ul><li>Sponsor confirmed – December 2009 </li></ul><ul><li>Draft PMP/Feasibility Cost Sharing Agreement – Jan-March 2010 </li></ul><ul><li>Finalize PMP (costs/task assignments) – April - June </li></ul><ul><li>PMP/FSCA Processing/Reviews – July – August 2010 </li></ul><ul><li>Signed Agreement – August 2010* </li></ul><ul><li>Start Feasibility – September 2010 </li></ul><ul><li>*Sign agreement by August 2010. Limited funding in Recon to keep a study moving with no sponsor. </li></ul>
    15. 15. Questions? Conowingo Dam ETM