This document discusses the functions and values of rivers. It defines a river and explains that rivers are dependent on their watershed characteristics like geology, soils, land use, vegetation and stormwater management. Urbanization can negatively impact rivers by increasing impervious surfaces and altering natural hydrologic patterns. To maintain natural river conditions, development must balance pre- and post-development flows through techniques like floodplain preservation, stormwater basins, and using accurate precipitation data. Overall, the document emphasizes that rivers are complex ecosystems that require consideration of their full watershed to support natural hydrologic and ecological functions.

1. 2012
Overview: The Functions &
Values of Rivers
Patrick C. Garner, Patrick C. Garner Co., Inc.

2. How Do We Define A River?
 A river is “any natural
flowing body of water that
empties into any ocean,
lake, pond, or other river
and which flows
throughout the year.”
(310 CMR 10.04)
 That’s only a start. Let’s
dive 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: Surficial
Geology

6. Watershed Area: Aerial
Analysis

7. Surficial Geology
 On a broad basis, watershed soils are
defined as tills and/or as “stratified drift.”
 Stratified drift is sand and gravel deposits
that have been layered and sorted by glacial
meltwater streams.
 Tills are mixed and often highly compressed
silts, sands & clay.

8. Glacial Impacts in New England
 Most of New England’s geology was formed
during the last ice age which retreated ~12-
14,000 years ago, and by subsequent wind
and water processes.
 Our landscape features--surficial patterns of
till and stratified drift deposits--were created
by the repeated movement of glaciers across
the landscape.
 Ice melt patterns during glacial retreat created much
of the topography that now underlies our rivers

9. Glacial Processes

10. Land Use
Considerations
 Urbanization--which rarely balances flows
and provides minimal drainage mitigation--
has changed the character and functions of
all small and large rivers.
 Urbanization typically increases impervious
area, decreases vegetative cover and--
through manmade drainage systems--
transports stormwater to rivers far faster than
under pre-development conditions.

11. Hydrologic Responses
to 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 A
Characteristic of Urbanization

14. Impacts of Urbanization

15. Typical Urbanization
“Armored” Stream in Chelmsford

16. Impacts of Urbanization

17. Vegetative
Changes Increase in
impervious area over a
30-year period, 1965-
1995, 100-acre site in
Tioga County, Penn.
1965
1995

18. Vegetative Changes
 Without mitigation,
decreased vegeta-
tion = increased
stormwater.
1982
2007

19. Management of Drainage
 Contemporary design attempts to balance
pre- and post-development peak flows
 Increased impervious area increases volume
of stormwater
 Sensitive design attempts to recharge and
retain the increased volume
 On a watershed basis, post-development
stream dynamics should mimic pre-
development (or natural) stream dynamics.

20. Common Management
Techniques
 Use of various stormwater basins
 Wet basin on the left, detention basin right

21. Basin
EffectsControlled release of stormwater
Decrease of peak rates

22. Maintaining Base
Flows
 Basins alone do not mimic natural recharge,
so infiltration techniques become critical to
maintain long-term stream flow.
Perforated pipe Leaching “pits”

23. Improper Design May Cause
Massive Structural Failure
 Improperly sized basins collapse
 Roadways and embankments too often
end up in downstream rivers

24. Stream Quality Is Often Not the
Only Victim of Poor Design
 2006 flooding
in New
Hampshire
Results of improper
culvert design.

25. Floodplains Are Critical
 Decreased floodplain storage alters
stream dynamics
 Stream base flow decreases in direct
proportion to decreases in floodplain
 Stream velocities increase as
floodplains decrease
 Wildlife habitat decreases dramatically
as floodplain disappears

26. 26
Using Correct Precipitation Data
 Extreme precipitation data for our
region and state has been updated in
the last year through a collaborative
effort between Cornell Univ & NRCS.
 An extreme precip website has just
come out of beta testing. See
http://precip.eas.cornell.edu/
26

27. 2727

28. 28

29. 29
100-year storm, Worcester
County, Massachusetts

30. 30

31. 31
Correct Rainfall Data = Correct
Culvert Sizing
 For over a half century regional
engineers have used a document
called TP-40, a federal extreme precip
atlas that predicts 2-100-year rainfall
events.
 TP-40 itself was based on rainfall data
from the 1940s and 1950s that experts
now recognize as representing a period
of cyclical drought. 31

32. 32
Course Corrections
 By the late 1990s climatologists
became aware that real world storm
events were not matching those
actually occurring.
 Storms that were supposed to occur
once every 50 and 100 years (based on
TP-40) were happening as frequently
as every 5 years.
32

33. 33
Increasely Large & More
Frequent Storms Are Projected
 Cornell University, through the NE
Regional Climate Center (NRCC), and
Natural Resources Conservation
Service (NRCS) have collaborated to
create a more accurate database of
precipitation data.
 Revised storm events for 100-year
events are 25-30% larger than what
was projected in TP-40. 33

34. 34
Ignore Reality At Public Peril
 When reviewing and approving new
roads, and replacement culverts, it is
essential to verify that correct rainfall
data has been used to size stormwater
structures.
 Real world, larger storm events require
larger culverts, larger storm basins and
more robust mitigation.
34

35. 35
Verdict?
 Rivers are almost always the final
recipients of storm water discharge.
 Use of incorrect rainfall data
guarantees that balancing pre- and
post-develop-ment flows will not
succeed. Increased stormwater flows
will acerbate swollen rivers and
heighten floodplain impacts.
35

36. 36
Good planning encourages...
 Preserving the entirety of a river, that is,
it’s channel and the historic horizontal
extent of its natural floodplain.
 Natural corridors protect both public
infrastructure, and protect wildlife.
36

37. Natural Corridors

38. 38
Unnatural Corridors
The Chickley River, Hawley (June 2012)
The Chickley River, Hawley (June 2012)

39. 39
Unnatural Corridors
The Chickley River, Hawley (June 2012)
The Chickley River, Hawley (June 2012)

40. 40
Chickley
River
before
2011 Work
Dec. 2010 (photo by
Little Bang Theory)
Dec. 2010 (photo by
Little Bang Theory)
Dec. 2010 (photo by
Little Bang Theory)

41. Ecological Relationship of
River Floodplains & Wildlife

42. Summary…
 Rivers are a deceptively
complex ecosystem
 Hydrologically, to
maintain “natural”
conditions, rivers are
watershed dependent
 Watersheds are sensitive
to % of impervious area,
floodplain storage &
changes in vegetative
cover
 Use of contemporary
rainfall data is essential

43. Acknowledgments
 Images by Patrick Garner; Gardner Bent, USGS;
Heidi Davis, Mass DEP; NRCS; USF&W; MassGIS &
others.