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Overview: The Functions & Values of Rivers …

Overview: The Functions & Values of Rivers
Patrick C. Garner
Patrick C. Garner, Co, Inc.

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  • 1. 2012Overview: The Functions &Values of RiversPatrick C. Garner, Patrick C. Garner Co., Inc.
  • 2. How Do We Define A River? A river is “any naturalflowing body of water thatempties into any ocean,lake, pond, or other riverand which flowsthroughout the year.”(310 CMR 10.04) That’s only a start. Let’sdive down a bit…
  • 3. Watershed Characteristics• Area• Surficial Geology• Underlying Soils• Land Use Considerations• % of Impervious Cover• Vegetative Characteristics• Stormwater Management• Floodplain Functions• Maintaining Natural Conditions• Habitat Preservation• Preserving Human Communities
  • 4. Watershed Area:USGS
  • 5. Watershed Area: SurficialGeology
  • 6. Watershed Area: AerialAnalysis
  • 7. Surficial Geology On a broad basis, watershed soils aredefined as tills and/or as “stratified drift.” Stratified drift is sand and gravel depositsthat have been layered and sorted by glacialmeltwater streams. Tills are mixed and often highly compressedsilts, sands & clay.
  • 8. Glacial Impacts in New England Most of New England’s geology was formedduring the last ice age which retreated ~12-14,000 years ago, and by subsequent windand water processes. Our landscape features--surficial patterns oftill and stratified drift deposits--were createdby the repeated movement of glaciers acrossthe landscape. Ice melt patterns during glacial retreat created muchof the topography that now underlies our rivers
  • 9. Glacial Processes
  • 10. Land UseConsiderations Urbanization--which rarely balances flowsand provides minimal drainage mitigation--has changed the character and functions ofall small and large rivers. Urbanization typically increases imperviousarea, decreases vegetative cover and--through manmade drainage systems--transports stormwater to rivers far faster thanunder pre-development conditions.
  • 11. Hydrologic Responsesto Urbanization Increased Discharge Increased Peak Discharge Increased Velocities Shorter time to peak flow Increased bankfull events Increased flooding Lower base flow Less groundwater discharge
  • 12. From Schuler, Maryland
  • 13. Stream Flooding As ACharacteristic of Urbanization
  • 14. Impacts of Urbanization
  • 15. Typical Urbanization“Armored” Stream in Chelmsford
  • 16. Impacts of Urbanization
  • 17. VegetativeChanges Increase inimpervious area over a30-year period, 1965-1995, 100-acre site inTioga County, Penn.19651995
  • 18. Vegetative Changes Without mitigation,decreased vegeta-tion = increasedstormwater.19822007
  • 19. Management of Drainage Contemporary design attempts to balancepre- and post-development peak flows Increased impervious area increases volumeof stormwater Sensitive design attempts to recharge andretain the increased volume On a watershed basis, post-developmentstream dynamics should mimic pre-development (or natural) stream dynamics.
  • 20. Common ManagementTechniques Use of various stormwater basins Wet basin on the left, detention basin right
  • 21. BasinEffectsControlled release of stormwaterDecrease of peak rates
  • 22. Maintaining BaseFlows Basins alone do not mimic natural recharge,so infiltration techniques become critical tomaintain long-term stream flow.Perforated pipe Leaching “pits”
  • 23. Improper Design May CauseMassive Structural Failure Improperly sized basins collapse Roadways and embankments too oftenend up in downstream rivers
  • 24. Stream Quality Is Often Not theOnly Victim of Poor Design 2006 floodingin NewHampshireResults of improperculvert design.
  • 25. Floodplains Are Critical Decreased floodplain storage altersstream dynamics Stream base flow decreases in directproportion to decreases in floodplain Stream velocities increase asfloodplains decrease Wildlife habitat decreases dramaticallyas floodplain disappears
  • 26. 26Using Correct Precipitation Data Extreme precipitation data for ourregion and state has been updated inthe last year through a collaborativeeffort between Cornell Univ & NRCS. An extreme precip website has justcome out of beta testing. Seehttp://precip.eas.cornell.edu/26
  • 27. 2727
  • 28. 28
  • 29. 29100-year storm, WorcesterCounty, Massachusetts
  • 30. 30
  • 31. 31Correct Rainfall Data = CorrectCulvert Sizing For over a half century regionalengineers have used a documentcalled TP-40, a federal extreme precipatlas that predicts 2-100-year rainfallevents. TP-40 itself was based on rainfall datafrom the 1940s and 1950s that expertsnow recognize as representing a periodof cyclical drought. 31
  • 32. 32Course Corrections By the late 1990s climatologistsbecame aware that real world stormevents were not matching thoseactually occurring. Storms that were supposed to occuronce every 50 and 100 years (based onTP-40) were happening as frequentlyas every 5 years.32
  • 33. 33Increasely Large & MoreFrequent Storms Are Projected Cornell University, through the NERegional Climate Center (NRCC), andNatural Resources ConservationService (NRCS) have collaborated tocreate a more accurate database ofprecipitation data. Revised storm events for 100-yearevents are 25-30% larger than whatwas projected in TP-40. 33
  • 34. 34Ignore Reality At Public Peril When reviewing and approving newroads, and replacement culverts, it isessential to verify that correct rainfalldata has been used to size stormwaterstructures. Real world, larger storm events requirelarger culverts, larger storm basins andmore robust mitigation.34
  • 35. 35Verdict? Rivers are almost always the finalrecipients of storm water discharge. Use of incorrect rainfall dataguarantees that balancing pre- andpost-develop-ment flows will notsucceed. Increased stormwater flowswill acerbate swollen rivers andheighten floodplain impacts.35
  • 36. 36Good planning encourages... Preserving the entirety of a river, that is,it’s channel and the historic horizontalextent of its natural floodplain. Natural corridors protect both publicinfrastructure, and protect wildlife.36
  • 37. Natural Corridors
  • 38. 38Unnatural CorridorsThe Chickley River, Hawley (June 2012)The Chickley River, Hawley (June 2012)
  • 39. 39Unnatural CorridorsThe Chickley River, Hawley (June 2012)The Chickley River, Hawley (June 2012)
  • 40. 40ChickleyRiverbefore2011 WorkDec. 2010 (photo byLittle Bang Theory)Dec. 2010 (photo byLittle Bang Theory)Dec. 2010 (photo byLittle Bang Theory)
  • 41. Ecological Relationship ofRiver Floodplains & Wildlife
  • 42. Summary… Rivers are a deceptivelycomplex ecosystem Hydrologically, tomaintain “natural”conditions, rivers arewatershed dependent Watersheds are sensitiveto % of impervious area,floodplain storage &changes in vegetativecover Use of contemporaryrainfall data is essential
  • 43. Acknowledgments Images by Patrick Garner; Gardner Bent, USGS;Heidi Davis, Mass DEP; NRCS; USF&W; MassGIS &others.