DTIC ADA407415: Considerations for Dam Removal in Ice-Affected Rivers. Ice Engineering. Number 27, January 2001

5 Pages·0.97 MB·English

by  Defense Technical Information Center

Ice Engineering
U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire
Considerations for Dam Removal
in Ice-Affected Rivers
During the past several hundred releases of sediment if dam removal is growth and progression, ice cover
years, many dams have been built in undertaken without an adequate sedi- breakup, and the movement and jam-
the United States to meet the power, ment management plan. This is par- ming of ice. In several cases, dam re-
water supply, flood control, and rec- ticularly important in impoundments moval has resulted in increased fre-
reational needs of a variety of users. known to contain contaminated sedi- quency and severity of downstream
The National Research Council esti- ments or fluvial tailings. ASCE (1997) jams (Fig. 1). Furthermore, lowering
mates that there are about 2.5 million provides a process for formulating of water levels in impoundments con-
dams in the United States, ranging sediment management plans associ- taining sediment deposits may result
from small farm pond dams to large ated with dam removal. USACE in more frequent or longer duration
hydropower dams (NRC 1992). (1983) also addresses sediment man- ice-induced scour and erosion of bed
Recently, increased awareness of agement following dam removal and bank material. This is particularly
the ecological, recreational, economic, under open-water conditions. important in impoundments where
and safety issues associated with In northern rivers, dam removal contaminated sediments have been
dams has led to a reevaluation of the and ensuing changes in hydraulic deposited during the lifetime of the
continuing existence of a number of regime cause changes to the ice dam.
dams. American Rivers et al. (1999) regime that may have significant local Ice-related adverse effects associ-
identified 467 dam removals in 43 impacts on ice formation, ice cover ated with dam removal can be miti-
states since 1912, with most removals
in the latter part of that century (92 in
the 1980s and 177 in the 1990s). Re-
mediation or mitigation of ecological
impacts are cited as the primary cause
for many recent dam removals. Dam
safety concerns and the costs associ-
ated with rehabilitation to meet dam
safety criteria or environmental re-
quirements also lead to dam removal
(ASCE 1997).
Ecologically based dam removal
often seeks to reestablish the pre-dam
hydraulic regime of the river, which
in turn can significantly affect the
timing and peak values of flood hy-
drographs. As a result, typical dam
removal studies (e.g., ASCE 1997)
address open-water impacts of dam
removals.
Another critical aspect of dam re- Figure 1. March 1968 ice jam on the Israel River at Lancaster, New Hamsphire. Ice jams
moval is the potential for adverse af- increased in frequency and duration here following the failure or removal of four dams on
fects that can result from uncontrolled the river between 1936 and 1950.
Number 27 January 2001
Report Documentation Page
Report Date Report Type Dates Covered (from... to)
00 Jan 2001 N/A -
Title and Subtitle Contract Number
Considerations for Dam Removal in Ice-Affected Rivers
Grant Number
Program Element Number
Author(s) Project Number
Task Number
Work Unit Number
Performing Organization Name(s) and Address(es) Performing Organization Report Number
USACE Engineer Research and Development Center Cold
Regions Research and Engineering Laborator 72 Lyme
Road Hanover, New Hampshire 03755-1290
Sponsoring/Monitoring Agency Name(s) and Sponsor/Monitor’s Acronym(s)
Address(es)
Sponsor/Monitor’s Report Number(s)
Distribution/Availability Statement
Approved for public release, distribution unlimited
Supplementary Notes
The original document contains color images.
Abstract
Subject Terms
Report Classification Classification of this page
unclassified unclassified
Classification of Abstract Limitation of Abstract
unclassified UU
Number of Pages
4
forces. This usually results from in-
creases in flow that are caused by a
rapid snowmelt or precipitation com-
bined with snowmelt. During me-
chanical breakup, the ice cover rapidly
breaks into smaller pieces that are
transported downstream until the
transport capacity of the river is ex-
ceeded. This may occur because the
moving ice rubble has reached an
intact ice cover or other obstacle that
resists movement, or can occur under
favorable hydraulic or morphological
conditions (e.g., decrease in energy
slope, increase in channel depth or
width).
Once a jam is initiated, incoming
Figure 2. The ice regime following dam removal can cause jams to form in places where
ice and flow build up to cause in-
they had not been previously observed. Shown here is a freezeup ice jam that formed on
creased forces that can result in jam
the Kennebec River, Augusta, Maine, in February 2000, following the removal of the
failure. Jam failure can be quite
Edwards Dam. Historical records indicate that jams occurred near here between 1794 and
sudden, with observed sustained ice
1835, when the dam was constructed.
floe and water velocities of 5 m/s (16
gated through ice control measures. thermal processes or from mechanical ft/s) or more (Andres and Doyle 1984,
An understanding of the ice regime processes such as juxtaposition, Jasek 1997). These surges can cause
and sediment geochemistry and mor- which forms a single layer accumula- significant erosion to bed and banks,
phology at an existing dam site is tion. Where velocities are higher, resulting in high concentrations of
required prior to removal so that ice shoving may result in multiple-layer suspended sediment. Or, the jam may
control and sediment stability mea- ice accumulations. remain in place as discharge drops,
sures can be included as part of a re- Once an ice cover forms, it can eventually freezing in place if tem-
moval project where necessary. Thus, thicken because of thermal processes peratures are cold, or melting out if air
the removal of dams in northern or by deposition of frazil or ice pieces and water temperatures remain warm.
rivers should not be undertaken with- beneath the ice cover. Frazil deposits Because of their additional thickness
out first studying potential impacts under ice (sometimes called hanging and increased roughness, jams that
on the ice regime and ice-affected dams) can become quite thick, de- freeze in place during midwinter can
mobilization of sediments impounded creasing flow area and increasing ve- cause significant erosion to bed and
behind dams (Fig. 2). This Ice Engi- locities beneath the ice. Frazil deposits banks compared to a normal ice cover.
neering Information Exchange Bulletin are often located at the upstream end
discusses the potential effects of dam of an impoundment where the energy Potential effects of dam
removal on river ice regime and pro- slope changes from steep to mild. removal in ice-covered rivers
vides guidelines for use when con- These deposits may provide a natural Dam removal can affect the ice
sidering dam removal in ice-affected impediment to the downstream move- regime both upstream and down-
rivers. ment of broken ice or ice runs later in stream from the dam site. If the dam is
the season, and can result in local located on a steep river, its removal
Background scour. may result in a steep, turbulent reach
The impoundment formed by a Ice cover breakup can be caused by that produces frazil instead of the
dam is generally characterized by rel- thermal processes (i.e., the cover melts slower-moving impoundment that
atively deeper, slower-moving water and thins as a result of warming air captured it. Thus, ice covers down-
compared to conditions upstream and water temperatures) or mechani- stream are likely to be thicker as a
from the impoundment or down- cal processes. Thermal breakup is result of incorporating the additional
stream from the dam. Ice covers tend largely benign, although it can result ice volume, either through juxtaposi-
to form more quickly in these slower- in the movement of ice pieces that tion, shoving, or deposition of frazil
moving areas than in the more tur- later jam. Mechanical breakup occurs ice. Locations with thicker ice covers
bulent downstream and upstream when the mechanical forces on the ice can become impediments to ice move-
reaches. The ice cover may form from cover become larger than the resisting ment during breakup. Increasing the
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overall volume of ice also may result structural ice control methods are considering removal of a dam. Their
in thicker downstream jams, or in the necessary, design and construction six-phase process includes an evalu-
formation of jams in areas that did not should be included as part of the dam ation of flood hazards and the devel-
experience jams while the dam was in removal plan. White and Moore (in opment of a sediment management
place (Fig. 2). Jams that might for- prep) discuss potential impacts of plan. Data collection required to sup-
merly have occurred at the upstream dam removal on river ice regime and port this process is also presented.
end of the impoundment because of provide two case studies in which However, the guidelines do not ad-
loss of energy gradient could form in- dam removal has required the later dress the potential impacts of dam re-
stead at another location downstream. construction of ice control structures. moval on ice regime. In order to iden-
Increased riverbed scour and ero- Two other cases in which ice regime is tify the likelihood of adverse effects
sion that will occur within the former important are also presented, one of occurring in ice-affected rivers be-
impoundment under open water con- which involves the movement of flu- cause of dam removal, the following
ditions because of increased near-bed vial tailings during ice events. additional steps are recommended for
velocity will be exacerbated by the ice-affected rivers:
presence of the ice cover. Moving or Recommended studies 1. Characterize the existing ice
jammed ice will significantly increase for ice-affected rivers regime, including formation, growth,
scour within the former impound- ASCE (1997) provides guidelines breakup, transport, and jamming in
ment and at downstream locations for studies to be undertaken when the reaches upstream and down-
where jams now form. Ice jam events
can mobilize large amounts of sedi-
ment (Fig. 3).
It is possible for ice jam flooding to
lower contaminant levels by deposit-
ing large amounts of cleaner sedi-
ments from scoured banks on the con-
taminated material, as long as clean
sediments exist. However, ice jam
flooding can also increase contamina-
tion when contaminated bed or bank
soils are eroded and deposited else-
where. If dams are removed and ice
events increase in severity, ice jam
events will “short circuit” the normal
sediment-trapping capability of res-
ervoirs and increase the release of con-
taminated sediments downstream.
The only remedy for this is to com-
pletely remove sediment before dam
removal or protect sediment from ice
erosion under the new hydraulic re-
gimes established after dam removal.
Some effects of dam removal on
riverine ice regime can be mitigated
using standard ice mitigation tech-
niques, such as those suggested by
Tuthill (1995) and Haehnel (1998).
Monitoring of ice conditions while the
dam is still in place is vital to deter-
mining its role in the ice regime and
predicting potential impacts associ-
ated with dam removal. Historical Figure 3. The erosion and scour of fluvial tailings can be dramatic during ice events. Here,
records should be examined to obtain metals concentrations measured in the Clark Fork River upstream and downstream from
information on pre-dam conditions as the Milltown Dam reservoir are shown following the ice jam event of February 1996.
well as current conditions. Where (After Moore and Landrigan 1999.)
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stream from the dam. Information evaluation of dam removal in ice- This issue of Ice Engineering was
on local ice processes may be found affected rivers may decrease the like- written by Kathleen D. White, Research
in the CRREL Ice Jam Database (http: lihood of adverse impacts. Hydraulic Engineer, Ice Engineering
//www.crrel.usace.army.mil/ierd/ Group, RS/GIS/Water Resources Branch,
icejam/icejam.htm) or USGS records. References U.S. Army Cold Regions Research and
At least one winter of ice monitoring American Rivers, Friends of the Engineering Laboratory (CRREL), En-
should be performed. Earth, and Trout Unlimited (1999) gineer Research and Development Center
2. Characterize the ice regime that Dam Removal Success Stories. Wash- (ERDC).
existed prior to dam construction. ington, DC: American Rivers. Editing and layout were done by Gioia
This will involve a search of historic American Society of Civil Engineers Cattabriga, Information Technology Labo-
records. Again, USGS records and the (1997) Guidelines for Retirement of Dams ratory, ERDC.
CRREL Ice Jam Database may contain and Hydroelectric Facilities. Washing- Funding was provided by the Civil
information useful in characterizing ton, DC: American Society of Civil Works Cold Regions Engineering Pro-
the historic ice regime. Engineers. gram Work Unit 33202, Characterizing
3. Hydraulic modeling of the ice Andres, D.D., and P.F. Doyle (1984) Ice Impacts on Operation and Main-
conditions should be performed if Analysis of breakup and ice jams on tenance.
jams are known to occur near the Athabaska River at Fort McMurray,
dam, both with and without the dam Alberta. Canadian Journal of Civil En-
in place, to determine whether dam gineering, Vol. 11, p. 444–458.
removal will affect the hydraulic con- Haehnel, R.B. (1998) Nonstructural
ditions leading to jam formation. If the ice control. U.S. Army Cold Regions
modeling indicates that the jam loca- Research and Engineering Laboratory
tion will change, or severity will in- Special Report 98-14.
crease, ice mitigation measures should Jasek, M. (1997) Ice jam flood mecha-
be considered. Summaries of appli- nisms on the Porcupine River at Old
cable techniques may be found in Crow, Yukon Territory. In Proceedings,
Tuthill (1995) and Haehnel (1998). 9th Workshop on River Ice, 24–26 Sep-
4. Sediment management alterna- tember 1997, Fredericton, New Bruns-
Ice Engineering
tives that include riverbed or bank wick, p. 351–370. Information Exchange Bulletin
erosion or sediment stabilization Moore, J.N., and E.M. Landrigan
should include hydraulic modeling (1999) Mobilization of metal-contam- The Ice Engineering Information Exchange
Bulletin is published in accordance with AR
of ice conditions to identify areas of inated sediment by ice-jam floods.
25-30 as one of the information exchange
ice-induced scour and erosion. Environmental Geology, 37(1-2): 96–101. functions of the Corps of Engineers. It is
National Research Council (1992) primarily intended to be a forum whereby
Conclusions Restoration of Aquatic Ecosystems: information on ice engineering work done
or managed by Corps field offices can be
The decommissioning and removal Science, Technology, and Public Policy.
disseminated to other Corps offices, other
of dams in order to improve aquatic Washington, DC: National Academy U.S. Government agencies, and the engi-
habitat is becoming more frequent in Press. neering community in general. The purpose
of the Ice Engineering Information Exchange
the United States. However, two po- Tuthill, A.M. (1995) Structural ice con-
Bulletin is information exchange and not the
tential problem areas are largely being trol: Review of existing methods. U.S. promulgation of Corps policy; thus, guid-
ignored: the potential for increased Army Cold Regions Research and En- ance on recommended practice in any given
area should be sought through appropriate
frequency and severity of ice jams gineering Laboratory Special Report
channels or in other documents. This bulle-
downstream from these former dam 95-18. tin’s contents are not to be used for advertis-
sites because of changed hydraulic U.S. Army Corps of Engineers (1983) ing, publication, or promotional purposes.
Citation of trade names does not constitute
conditions, and, for northern rivers, Corps responsibilities for non-Federal
an official endorsement or approval of the
the potential for increased movement hydroelectric power development
use of such commercial products.
of contaminated sediments from the under the Federal Power Act. Engi- The U.S. Army Cold Regions Research
former dam impoundments during neer Regulation 1110-2-1454. Wash- and Engineering Laboratory (CRREL) is
part of the Corps of Engineers Engineer
the ice-covered period. The time to ington, DC: U.S. Army Corps of
Research and Development Center
design ice control measures is before Engineers. (ERDC).
dam removal, so that mitigation costs White, K.D., and J.N. Moore (in prep) Communications are welcomed. Write to
CRREL, ATTN: Tim Pangburn (RS/GIS/
can be included in the removal project Impacts of dam removal on riverine
WRB), 72 Lyme Road, Hanover, NH
cost-benefit analysis. Inclusion of the ice regime. Submitted to ASCE Journal 03755-1290, or call 603-646-4296.
steps recommended above during the of Cold Regions Engineering.
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