legacy sediment and pa’s chesapeake bay tributary
TRANSCRIPT
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Legacy Sediment and PA’s Chesapeake Bay Tributary Strategies
An Innovative BMP Proposal
Pennsylvania Tributary Strategy Steering Committee
Legacy Sediment Workgroup 2007
Jeffrey Hartranft
Bureau of Waterways Engineering
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Presentation Outline
• PA’s Tributary Strategy – A Timeline and Brief History
• Linking Policy and Science- Defining Legacy Sediment
• The Science
• Chesapeake Bay Watershed Model Phase 5.0
• Innovative New BMP and Innovative Uses of Existing BMP’s
• Future Considerations and ?’s
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PA’s Tributary Strategies – A Brief History• 2004 (December) Draft - PA Chesapeake Bay
Tributary Strategy Unveiled- “Working Document”
• 2005 Public meetings across PA-Strategy Feedback
• 2006 PA Creates Chesapeake Bay Tributary Strategy Steering Committee - Stakeholders
Specific Workgroups Organized
1) Point Source Workgroup
2) Agriculture Workgroup
3) Stormwater and Development Workgroup
4) Trading Workgroup
5) Legacy Sediment Workgroup – February 2006
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PA Legacy Sediment WorkgroupPA DEP
PA Fish and Boat Commission
PA Department of Transportation
PA Farm Bureau
PA State Association of Township Supervisors
US Environmental Protection Agency
US Geological Survey
Chesapeake Bay Commission
Chesapeake Bay Foundation
Academia (Franklin and Marshall College, Lafayette College, PSU)
Consultants (Landstudies Inc., Aquatic Resources Restoration Co.)
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Legacy Sediment DefinitionGeneric Definition
Legacy Sediment - Sediment that was eroded from upland areas after the arrival of early Colonial settlers and during centuries of intensive land uses; that deposited in valley bottoms along stream corridors, burying pre-settlement streams, floodplains, wetlands, and valley bottoms; and that altered and continues to impair thehydrologic, biologic, aquatic, riparian, and water quality functions of pre-settlement and modern environments. Legacy sediment often accumulated behind ubiquitous low-head mill dams and in their slackwater environments, resulting in thick accumulations of fine-grained sediment that contain significant amounts of nutrients.
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… more information and definitions
www.state.pa.us
PA Keyword : Chesapeake BayWorkgroup Products
Legacy Sediment Workgroup
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The Science Funding provided by the Chesapeake Bay Commission, Growing Greener and
Franklin & Marshall College
Lancaster, Pennsylvania
Walter, R., D. Merritts, M. Rahnis, 2007.Estimating volume, nutrient content, and rates of stream bank erosion of legacy sediments in the Piedmont and Valley and Ridge physiographic provinces, Southeastern and Central, PA.
PA DEP report draft- 38pp. (42 Figures; 12 Appendices)
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Gellis, et al. 2004 USGS
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Impact of Water-Powered Mills on Sediment Storage
dam
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Buried Colonial road and saw mill
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Buried pre-Colonial
wetland(11,500 to300 BP)
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Radiocarbon Dates
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Langland, et al. , 2002
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Legacy Sediment Volume, Erosion Rate and Nutrient Load Estimates
1. LiDAR derived bank height and valley fill area estimates - volume
2. Monumented cross section surveying and bank pins
3. Orthorectified imagery time series bank retreat estimates
4. Total Nitrogen and Total Phosphorous concentrations in legacy sediment
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Conclusions• Mill densities/PA County area were high in the 18th-early 20th c. (~6000 mills in the PA Chesapeake Bay watershed in 1840)
• Slackwater and backwater effects were several km on low-gradient streams of the Piedmont, and limestone streams of the Ridge and Valley where average dam heights are ~10 feet
• Stream corridors and valleys formed under natural geologic and climatic conditions are burried under legacy sediment today
•The pre-settlement stream corridors and valleys were comprised ofextensive forested, scrub-shrub, and herbaceous palustrine wetlands
• Bank erosion rates are highest where streams have incised through legacy sediment and estimates derived using 4 methods, for different scales of time (~2 to 100 yrs), range from 0.17 to 0.94 tons/ft/yr
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Conclusions
•Legacy sediments are nutrient-rich: 400-2100 ppm total N; 340-958 ppm total P
•Nutrient loads to streams based on bank erosion rates and nutrient concentrations in legacy sediment are a significant source of measured loads
•The stream corridor is a significant source of sediment and nutrients; it is rarely a significant sink for runoff from upland sources along incised channels
•The results could lead to a reallocation of sediment and nutrient sources in the Chesapeake Bay Watershed Model (Phase 5.0)
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Linker, 2006-USEPA
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Linker, 2006-USEPA
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Linker, 2006-USEPA
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Existing Condition
Flood Flow
Legacy Sediment
Bedrock
GravelBase Flow
~ 10 ft
Hydric Soils Hydric Soils
Root Zone
• The Existing Condition is < 300 years old
• Modern floodplain functions are severely compromised
• Legacy sediment is a modern nutrient and sediment source from bank erosion
• Indigenous streams, wetlands, floodplains, and vegetation are buried under legacy sediment
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Natural Condition
Base Flow
Bedrock
Flood Flow
GravelHydric Soils
Root Zone
• The Natural Condition formed under long-term geologic and climatic influences
• Contains natural and stable ecosystems adapted to the current climate
• Represents indigenous streams, wetlands, floodplains, and vegetation
• Functions as nutrient and sediment sinks
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Legacy Sediment Removal - Stream and Riparian Restoration Best Management Practice (LSR-SRR BMP)
BMP Conceptual DesignExisting Condition
Legacy Sediment
Flood Flow
Bedrock
GravelBase Flow
~ 10 ft
Hydric Soils Hydric Soils
Root Zone
Legacy Sediment
Proposed Restoration
Natural Condition
Base Flow
Bedrock
Flood Flow
GravelHydric Soils
Root Zone
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LSR-SRR BMP• The proposed BMP is an ecological restoration and management
strategy.
• Restoration and management actions are proposed to re-establish natural stream, wetland, floodplain and riparian condition and function.
• Implementing the practice will target legacy sediment.
• Careful monitoring, cost tracking, and documentation is essential to quantify benefits vs. cost.
• Recognizing the role that legacy sediment plays in modern environmental conditions, thereby understanding fundamental river impairments, will improve watershed and river management and restoration strategies in the Chesapeake Bay.
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Existing Condition
Legacy Sediment
Flood Flow
Bedrock
GravelBase Flow
~ 10 ft
Hydric Soils Hydric Soils
Root Zone
Legacy Sediment
Proposed Restoration
Natural Condition
Base Flow
Bedrock
Flood Flow
GravelHydric Soils
Root Zone
Legacy Sediment Removal - Stream and Riparian Restoration Best Management Practice (LSR-SRR BMP)
BMP Conceptual Design