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Design of a Dam Sediment Management System to Aid Water

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Design of a Dam Sediment Management System to Aid Water Design of a Dam Sediment Management System to Aid Water Quality Restoration of the Chesapeake Bay Presented By: Sheri Gravette Kevin Cazenas Said Masoud Rayhan Ain Sediment Plume from Transient Scouring Sponsors: Lower West & Rhode Susquehanna Riverkeeper Riverkeeper Dam Conowingo Faculty Advisor: George Donohue Agenda • Context • Stakeholders • Problem/Need Statement • Design Alternatives • Analysis and Design of Simulation • Design of Experiment • Results, Analysis & Recommendations 2 Chesapeake Bay and The Susquehanna River • Chesapeake Bay is the largest estuary in the United States • 3 largest tributaries of the Bay are the Susquehanna, Potomac and James rivers – Provide more than 80% of the Bay’s freshwater • Susquehanna River is the Bay’s largest tributary – Provides nearly 50% of freshwater to the Bay – Flows from NY to PA to MD Map of the Chesapeake Bay Watershed Source: The PA Dept. of Environmental Protection 3 Lower Susquehanna River and Conowingo Dam • Conowingo Dam (est. 1928) – southernmost Dam of the Lower Susquehanna • Quality of water from the Lower Susquehanna is vital to the bay’s health • Traps sediment and nutrients from reaching the Chesapeake Bay – Water quality is closely related to sediment deposition • The river provides power for turbines in hydroelectric plants and clean water to people • Conowingo Hydroelectric Station – Mainly provides power to Philadelphia, PA – A black start power source – Provides 1.6 billion kWh annually Map of Conowingo Reservoir Source: US Army Corps of Engineers, (2013) 4 Lower Susquehanna River: Steady State vs. Transient State Current Steady State: river flow rate Transient state: river flow rate higher less than 30,000 cfs than 300,000 cfs – Sediment/nutrients enters Chesapeake Bay at low-moderate rate – Major Scouring event: enhanced erosion of – TMDL regulations are related to steady sediment due to: state – significantly increased flow rates – constant interaction of water with the Dam Chesapeake Bay: Before and After Tropical Storm Lee Source: MODIS Rapid Response Team at NASA GSFC 5 Flow and Sediment Build-up in Conowingo Reservoir • Rouse number defines a concentration profile of sediment – Determines how sediment will be Holtwood Dam transported in flowing water • Rouse Number: 흎 풁 = 풔 풖∗ 흎풔=Sediment fall velocity 풖∗=shear velocity • Significant amount of suspended sediment is located directly behind the dam (areas away from turbines) Conowingo Dam Rouse Number for Medium Silt Particle at 30,000 cfs 6 Source: S. Scott (2012) Sediment Deposition at Conowingo Dam 100% 200 Sediment Deposition • Deposition potential – Expected 90% ) Threshold expected sediment 80% deposited over a given 150 70% time (million tons (million 60% 100 50% • At maximum capacity all 40% Susquehanna River Percent Capacity Percent 30% sediment flow s through 50 20% to the Chesapeake Bay Sediment Deposition Deposition Sediment 10% during normal, steady- 0 0% state flow 1929 1936 1943 1950 1957 1964 1971 1978 1985 1992 1999 2006 2013 2020 2027 Year Sediment Deposition in Conowingo Reservoir; Construction to 2008 with Gap Prediction Source of Data: Hirsch, R.M., (2012) 7 Chesapeake Bay Total Maximum Daily Load (TMDL) • Established by US Environmental Protection Agency in conjunction with 1972 Clean Water Act • Actively planned since 2000 • Covers 64,000 square miles in NY, PA, DE, MD, WV, VA, and DC • Sets limits for farmers, plants, dams, and other organizations that dump sediment/nutrients into dam • Designed to fully restore Bay by 2025 – 2017: 60% of sediment/nutrient reduction must be met 8 Lower Susquehanna Contribution to TMDL Watershed limits to be attained by 2025 are as follows: • 93,000 tons of nitrogen per year (46% of Chesapeake TMDL reduction) • 1,900 tons of phosphorus per year (30% of Chesapeake TMDL reduction) • 985,000 tons of sediment per year (30% of Chesapeake TMDL reduction) 9 Agenda • Context • Stakeholders • Problem/Need Statement • Design Alternatives • Analysis and Design of Simulation • Design of Experiment • Results, Analysis & Recommendations 10 Primary Stakeholders Objective(s) Issue(s) Lower Susquehanna - Find alternative uses for the sediment stored - Cost to remove sediment from Reservoir is Riverkeeper and Stewards of behind Conowingo Dam high the Lower Susquehanna, Inc. - Highlight vulnerabilities in environmental law - Providing pressure on FERC to require more (SOLs) - Minimize effects of major scouring events to strict relicensing requirements for Conowingo the Chesapeake Bay Dam Hydropower Plant Chesapeake Waterkeepers- - Protect and improve the health of the - Cost to remove sediment from Reservoir is West & Rhode Riverkeeper Chesapeake Bay and waterways in the region high Maryland and Pennsylvania - Maintain healthy waters for fishing and - Cost to remove sediment from Reservoir is Residents (Lower recreation high Susquehanna Watershed) - Improve water quality of the watershed - Value low cost for power production and - Receive allocated power from Hydroelectric better water quality Dam Exelon Generation – owner of - Obtain relicensing of Conowingo Dam prior to - Sediment build up has no impact on energy Conowingo Dam its expiration in September 2014 production - Maintain profit Federal Energy Regulatory - Aid consumers in obtaining reliable, efficient - Pressure to update dam regulations Commission (FERC) and sustainable energy services - Define regulations for energy providers 11 Agenda • Context • Stakeholders • Problem/Need Statement • Design Alternatives • Analysis and Design of Simulation • Design of Experiment • Results, Analysis & Recommendations 12 Problem Statement - Conowingo Reservoir has been retaining a majority of the sediment flowing down the Susquehanna River - Major scouring events in the Lower Susquehanna River perpetuate significant ecological damage to the Chesapeake Bay - This ecological damage is caused by increased deposition of sediment and nutrients in the Bay 13 Need Statement • Need to create a system to reduce the environmental impact of transient scouring events • Need is met by reducing the sediment and nutrients currently trapped behind Conowingo Dam – Reduce to 1,900 tons phosphorus per year • Reduction is to be done while maintaining energy production and aiding TMDL regulations 14 Mission Requirements MR.1 The system shall remove sediment from the reservoir such that the total sediment deposition does not exceed 180 million tons. MR.2 The system shall reduce sediment scouring potential. MR.3 The system shall allow for 1.6 billion kWh power production annually at Conowingo Hydroelectric Station. MR.4 The system shall facilitate Susquehanna watershed limits of 93,000 tons of nitrogen, 1,900 tons of phosphorus, and 985,000 tons of sediment per year by 2025. MR.5 The system shall facilitate submerged aquatic vegetation (SAV) growth in the Chesapeake Bay. 15 Agenda • Context • Stakeholders • Problem/Need Statement • Design Alternatives • Analysis and Design of Simulation • Design of Experiment • Results, Analysis & Recommendations 16 Sediment Mitigation Alternatives 1. No Mitigation Techniques (Baseline) – Sediment remains in reservoir 2. Hydraulic Dredging – Sediment removed from waters – Product made from sediment 3. Dredging & Artificial Island – Initially: Sediment is dredged to make an artificial island – Over time: Sediment is slowly forced through the dam into bay Conowingo Dam Source: D. DeKok (2008) 17 1. No Mitigation 2. Hydraulic 3. Dredging & Techniques Dredging Artificial Island WHAT HOW • Sediment will reach capacity • Normal Flow: < 30,000 cfs by 2030 • Major Scouring Event: > 300,000 cfs • Major scouring events will have the largest impact Normal Flow at Conowingo Dam Source: E. Malumuth (2012) 18 1. No Mitigation 2. Hydraulic 3. Dredging & Techniques Dredging Artificial Island WHAT HOW • Remove sediment mechanically • Rotating cutter to agitate & stir up • Concentration on suspended sediment • Pipeline pumps sediment to surface • Product yield from sediment • Collection for further treatment Hydraulic Dredging Process Source: C. Johnson 19 1. No Mitigation 2. Hydraulic 3. Dredging & Techniques Dredging Artificial Island WHAT • Diamond-shaped structure to divert water is placed in front of the dam • Larger sediment load through the dam (at steady-state); remaining amount is dredged HOW • Diverter made of dredged sediment product • Diverts water left & right – increases flow velocity • Decreases Rouse number near suspended sediment • Sediment mixed into wash load • Potentially decreases total dredging costs Potential Artificial Island Location at Conowingo Reservoir Source: Original graphic by S. Scott (2012) 20 Primary Alternatives Sub-Alternatives 1. No Mitigation 2. Hydraulic 3. Dredging & Techniques Dredging Artificial Island Low Temperature Plasma Gas Arc Quarry Rotary Kiln Washing Vitrification Quarry • Direct transportation from reservoir to quarry • No opportunity to offset cost • No one-time investment cost Rock Quarry 21 Primary Alternatives Sub-Alternatives 1. No Mitigation 2. Hydraulic 3. Dredging & Techniques Dredging Artificial Island Low Temperature Plasma Gas Arc Quarry Rotary Kiln Washing Vitrification Low-Temperature Sediment Washing • Process includes: • Non-thermal Decontamination – Loose screening • Potential use as manufactured – Dewatering topsoil – Aeration • One-time cost: Approx. $25 – Sediment washing/remediation million (BioGenesis) – Oxidation and cavitation Low Temperature Washing Facility Manufactured Topsoil 22 Primary Alternatives Sub-Alternatives 1. No Mitigation 2. Hydraulic
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