This
paper was written as part of the 2001 Alaska Ocean Sciences Bowl high
school competition. The conclusions in this report are solely those
of the student authors.
Natural and Human History of the Mendenhall
Watershed near Juneau, Alaska: A plan for managing the watershed
Written in part by each
of the following:
Wesley Brooks
Cal Craig
Jeff Fanning
Breanne Rohm
Clay Good, coach
Team
Tsunami
Juneau-Douglas High
School
10016 Crazy Horse Dr.
Juneau, Alaska 99801
Table of Contents
Definition of the watershed (2.1)
Statement of purpose (2.2)
Salmon in the watershed (3.1)
Mendenhall Wetlands Game Refuge (3.2)
Waterfowl (3.2.1)
Other wetlands (3.3)
Riparian vegetation (4.1)
Water quality (4.2)
Iron flocculate (4.2.1)
Sedimentation (4.2.2)
Non-point source pollution (4.2.3)
Stream channel modifications (4.3)
Duck Creek (4.3.1)
Mendenhall River (4.3.2)
Expected changes in flow (4.4)
Impervious cover (5.1)
Recreational use (5.2)
Impacts of population increases (5.3)
Summary (6.1)
Mandates (6.2)
Funding and enforcement (6.2)
Sources (7.1)
Abstract (1)
The Mendenhall Watershed is the drainage area created by the most recent
recession of the Mendenhall Glacier north of Juneau, Alaska. In the
past fifty years, human development in the area has expanded dramatically,
bringing with it many adverse impacts to the so recently pristine watershed.
Particularly in the early days of development in the valley, the filling
of wetlands and channelization of streams proceeded unchecked, so that
today few wetland areas remain in the watershed. Duck Creek, once the
base of a large anadromous fish population, now runs almost dry through
much of the year. Roads built alongside streams carry chemicals into
the water from runoff and infringe upon necessary riparian zones. A
series of ponds dredged into Duck Creek to provide gravel for construction
have altered the flow and impaired water quality in that creek. Duck
Creek has become highly contaminated with iron flocculate (once oxidized
in the root rhizosphere of riparian plants before it could reach the
stream) and is also highly affected by sedimentation as a result of
sanding roads for traction on snow. Impervious cover roads, roofs, and
surfaces which don’t allow water to enter the ground where it would
normally be filtered through natural processes contributes to the low
flow problem as well. In the Mendenhall Watershed, this has become a
very real problem.
The Forest Service protects the northern reaches of the watershed as
part of the Mendenhall Glacier Recreation area in the Tongass National
Forest, and the State of Alaska protects the southern end of the watershed
as the Mendenhall Wetlands Game Refuge. Between these areas, the watershed
is managed by the City and Borough of Juneau.
Property along the Mendenhall River is now threatened by the constant
erosion of that river’s banks. To protect property, owners have
placed stone riprap on the streambanks, destroying fish habitat and
exacerbating erosion problems elsewhere.
To restore wild fish runs and preserve the social importance of the
watershed, a management policy which restores natural conditions where
possible and mitigates the effects of human development is needed. This
plan includes repairing impaired waterways and managing the continued
development of the watershed in such a way as to minimize its negative
environmental impacts.
Introduction (2)
Definition of the Watershed (2.1)
The Mendenhall Watershed is the drainage area created by the past
advances and recessions of the Mendenhall Glacier. The watershed consists
of a steep-sided mountain valley ten miles north of downtown Juneau,
Alaska (Figure 1). It is bounded
to the north by the Mendenhall Glacier and to the south by Gastineau
Channel, a shallow saltwater fjord. In 1750, when the glacier reached
its farthest downvalley position in the past 13,00 years, the land of
the watershed was almost completely hidden by ice, and was depressed
five feet below its current level (Carstensen, 1999). The northern part
of the watershed is protected as the Mendenhall Glacier Recreation area,
and managed by the U.S. Forest Service as part of the Tongass National
Forest. The southern area of the watershed is a saltwater wetland protected
by the Alaska Department of Fish and Game as a game refuge. Between
these protected areas, most of the land in the watershed to the east
of the Mendenhall River has been developed, while large areas remain
undeveloped to the west of the river. Human development began in the
1890s, before rapidly expanding in the 1960s. Wetlands were quickly
filled and built upon, and the forests of the valley were selectively
logged to provide building material. Rapid expansion of the human population
in the area continued into the 1980s, at which time the population growth
leveled out considerably (Figure 2).
The importance of wetlands to the watershed’s health was not recognized
during this period, and had current regulatory guides been followed,
they would have avoided much of the environmental damage in the watershed
during this expanding phase (Koski and Lorenz, 1999).
Statement of Purpose (2.2)
The Mendenhall Watershed is a valuable natural resource for all members
of the Juneau community. It is the intent of this report to identify
the forces and phenomena, both natural and human, which affect the Mendenhall
Watershed, and enumerate their impacts. The management plan contained
herein is based upon this analysis. Since most of the area of the Mendenhall
Watershed is owned by private citizens, any management plan should be
accepted voluntarily on a communitywide basis, and the initiative for
restorative action should come from the grassroots level. To this end,
there already exist a number of groups concerned about the fate of the
Mendenhall Watershed. The Duck Creek Advisory Group and the Mendenhall
Watershed Partnership are citizen organized bodies which work toward
improving the watershed and increasing public awareness and support
of their environmental goals in the Mendenhall Watershed.
Government’s role in the management of an urbanized watershed is
necessarily altered by the control private citizens hold over their
property. Regulations derived from the stipulations of the 1977 Clean
Water Act (CWA) exist for the protection of water resources, including
setbacks and buffers for identified anadromous fish streams. State and
local governments are obligated by the CWA and their own laws to preserve
the natural condition of streams. CBJ Land Use Ordinance 87-49 states
that streams in the CBJ "Shall be managed to protect natural vegetation,
water quality, important fish or wildlife habitat, and natural water
flow."
By looking ahead 50 years, this plan addresses the fact that no change
in something as dynamic as a watershed is simple or quick. Technology
and public opinion will change in the next 50 years, and those changes
will alter the implementation and direction of this plan.
Fish and Wildlife resources (3)
Salmon in the watershed (3.1)
The Mendenhall Watershed provides essential habitat for several species
of salmonids (i.e. salmon and trout). Juneau’s fisheries rely heavily
on the watershed and its ability to support these fish. The Mendenhall
River is the primary migratory corridor for all salmonids leaving and
entering the watershed. The banks of the river provide protection, cover,
erosion control, nutrients, and food, and its source, Mendenhall Lake,
provides a rearing habitat for Dolly Varden char and Cutthroat trout
(InterFluve, 1999). In varying years, the creeks supply up to 400 days
of fishing effort. Fish runs have precipitously declined in Duck Creek,
which at one time supported an excellent fishery. In 1929, Duck Creek
had a fish run of 50,000 chum salmon and in the 1960s the creek supported
a 500 chum salmon run (Koski and Lorenz, 1999).
Today, chum salmon are extinct from the creek, and it supports less
than 20 coho salmon (Koski and Lorenz, 1999). Researchers have concluded
that the decline in salmon reproduction in Duck Creek is largely due
to the quantitiy of fine sedimentation and low dissolved oxygen levels
in the streambed gravel (Koski and Lorenz, 1999). The annual escapement
of coho salmon in the Mendenhall River is 10,000 fish; 50% of the annual
return is harvested in either the commercial, sport, or subsistence
fishery (i.e. for every fish that makes it back to the drainage, one
is harvested in the ocean). With the assumption that 95% of the coho
salmon are taken in commercial fisheries and the other 5% are taken
for recreational or subsistence purposes, the dollar value of the fish
can be calculated for the commercial fisheries. The average price paid
to commercial fishers in 1998 for coho salmon was $4.62. If 9,000 fish
destined for the Mendenhall River drainage were caught by commercial
fishers, then the coho would be worth $43,890 to the commercial fishery
(InterFluve, 1999). However, the net value to the local economy is much
greater because commercial fishers expend great amounts of money purchasing
boats, equipment, safety gear, and licenses. A study conducted 10 years
ago indicated that marine recreational anglers in Southeast Alaska expended
$250 for every coho salmon harvested (Jones and Stokes, 1991).
The disappearance of salmon in the waterways of the Mendenhall Watershed
is troubling, because salmon are a good indicator of overall watershed
health. (Koski and Lorenz, 1999). The near extinction of all salmon
in Duck Creek is an indication of just how debilitated that environment
is. Subtle reductions in salmon returns to the Mendenhall River are
an indication that the health of that waterway is also beginning to
decline. The a major cause of that decrease may be armored riverbanks,
which offer little to no protection for rearing salmonids which live
in the river (InterFluve, 1999).
Mendenhall Wetlands Game Refuge (3.2)
The Mendenhall Wetlands stretch over 9 miles in a 4,000 acre refuge.
The diverse plant communities furnish food and shelter for more than
140 species of birds and over 12 species of mammals. The blend of the
watershed’s fresh water from the rivers and streams and the salt
water from the ocean form a rich environment for terrestrial and aquatic
plant life. The wetlands provide the Juneau community and visitors a
place for recreation and scenery. Hunters take over 3,000 ducks annually
on the refuge (ADF&G, 1997). Hunting and fishing are traditional
assets extremely important to Alaskan culture. The area south of the
Float Pond is located on the wetlands as a component of the Juneau Airport
and, surprisingly enough, the surrounding area, affected by the ponds
initial construction, has provided an excellent habitat for mammals,
fish, and waterfowl (Richard Carstensen, pers. comm.).
Waterfowl (3.2.1)
The Mendenhall Wetlands provide feeding grounds for birds migrating
north and south in the spring and fall, respectively, as well as a feeding
station for breeding birds during the summer (ADF&G, 1997). The
importance of this habitat to migratory birds means that any alterations
made to the wetlands could potentially have ramifications affecting
bird populations stretching southward into Mexico. The social impact
of these birds is hard to judge, since besides hunting, the refuge is
frequented by hundreds if not thousands of birdwatchers on an annual
basis.
Other wetlands (3.3)
There are numerous other small wetlands in the Mendenhall Watershed.
All are protected by state laws requiring special permitting for development
on wetlands. Widespread development took place in the area between the
years 1948 and 1984, but since then development and wetland filling
have slowed, following the trend of population growth in the area (InterFluve,
1999) (Figure 3).
Hydrology (4)
Riparian Vegetation. (4.1)
Riparian vegetation is the vegetation growing along the banks of creeks
and rivers which serves to provide habitat for both aquatic and terrestrial
species. It also filters water flowing into the stream, and reduces
temperature change (K Koski, pers. comm.). The vegetation acts as a
filtration system for the river, trapping pollutants already in the
water and also stopping pollutants from entering the water. Riparian
vegetation also protects the soils of the stream bank from being swept
away in periods of high flow (Muhlberg and Moore, 1998). Further, riparian
vegetation releases water absorbed during wet periods increasing flow
during dry periods, thus serving to maintain a constant stream flow.
When vegetation, including, large trees, fall into the creek, they create
eddies, riffles and pools, providing fish habitat. Aquatic insects feed
on wood and plant debris that fall into the water, and in turn are fed
upon by rearing fish.
Riparian vegetation on the stream bank is essential for a healthy watershed,
but vegetation along roads is equally important. In the Mendenhall Watershed
riparian vegetation is generally limited by the construction of roads
and houses. Cars are heavy polluters, giving off chemicals like leaking
oil, gasoline, antifreeze, brake pad dust, and rust. The water on the
roads contains high concentrations of pollutants. When the water runs
off the roads and runs directly into the stream without being filtered
by riparian vegetation, there are many negative environmental effects
caused by the introduction of the pollutants. If the water runs into
a drain and then into the stream it still contains the pollutants, and
if the water runs into a drain and then out to sea, the river is still
harmed by not receiving the water at all.
Bioengineered streambank protection can take many forms, from woody
plants and debris to hold the bank together and store more water in
the soil to plants specifically intended to oxidize iron in their roots
before it enters the stream. The type of riparian vegetation used in
bioengineering projects depends on the desired purpose.
Water quality (4.2)
Iron flocculate (4.2.1)
Duck Creek is the stream in the Mendenhall Watershed that is currently
most heavily affected by iron flocculate. Glaciomarine deposits in the
Mendenhall Watershed are high in iron content, which causes high levels
of iron ions in groundwater in the area. A 1968 survey found that groundwater
wells dug into floodplain sediments of the Mendenhall Watershed averaged
about 2.2 parts per million (ppm), while surface water in the same area
generally contained less than .3 ppm iron, the generally accepted maximum
level for domestic use (Barnwell and Boning, 1968) Before human settlement
in the watershed, there were two ways in which the areas streams were
naturally kept free of iron flocculate. First, numerous boggy marshes
served to oxidize the iron at the root rhizosphere of the plants and
keep it out of the streams. Second, faster flowing water in Duck and
Jordan Creeks served to wash away what iron flocculate did develop (Stahl,
1999). With the removal of the marsh areas, more dissolved iron was
free to enter the streams, and the slowing of the stream flows due to
reduced water input, sedimentation, and culverts, allowed more flocculate
to develop in Duck and Jordan Creeks. Iron ions will spontaneously react
with water molecules to form a number of compounds known as iron oxy-hydroxides.
It is deposits of these compounds which make up iron flocculate (Stahl,
1999). Because the groundwater contains very little dissolved oxygen,
the iron can remain dissolved in its ferrous (Fe2+) soluble form, but
when the inflowing groundwater mixes with surface water containing more
dissolved oxygen, the dissolved iron is oxidized. The ferric (Fe3+)
oxyhydroxide compounds are less soluble in water, and are deposited
as mats of iron flocculate (Beilharz, 1998).
These deposits fill in the small gaps in the gravel streambed, thus
impairing both salmon spawning habitat, as well as habitat for invertebrates
and insects which the juvenile fish feed on. Also, the chemical reaction
consumes dissolved oxygen, which leaves the stream less biologically
useful (Beliharz, 1998). In areas with heavy flocculate deposits, less
water filters through the streambed to reach the gravel 10-12 inches
below the streambed, which is where salmon lay their eggs (K Koski,
pers. comm.). Conditions with little intragravel flow and low dissolved
oxygen will kill the eggs. Because the iron flocculate problem happens
only where there is groundwater discharge, any iron conversion treatments
would have to take place at the site of the inflowing water (Beilharz,
1998).
Restoration of natural protection measures coupled with a mechanical
aeration device to oxidize iron before entering the stream seems to
be the most effective way to combat the iron flocculate problem. This
includes the creation of boggy marshes in developed areas with groundwater
upwellings. Certain species of plant particularly effective at oxidizing
iron in the root rhizosphere include cattails, rice plants, and reed
canary grass, all of which are exotic to the Southeast Alaska area (K
Koski, pers. comm.). Reed canary grass is the most feasible of these
plants because it is actively expanding the area it occupies along parts
of Duck Creek, and because it showed a strong tendency to significantly
reduce dissolved iron in a field test (Stahl, 1999). Because of its
aggressive nature and exotic status, though, reed canary grass is dangerous
to the native plants in the creek (Richard Carstensen, pers. comm.).
The mechanical aeration approach would require the construction of a
small facility to be operated by the City and Borough of Juneau. This
method would be the easiest to install, require the least maintenance
and would avoid the unnecessary introduction of exotic species into
the watershed. The cost to create the aeration facility would be about
$90,000 (Koski and Lorenz, 1999).
Increasing flow by the affected streams would help reduce iron flocculate,
because an increased stream flow would assist in washing present iron
flocculate out. This would also reduce the likelihood of total drying
of the Creek, improving its usefulness as fish habitat. Proposals to
increase stream flow have centered upon the possibility of renovating
an old pipeline from Nugget Creek, which is located three miles north
of Duck Creek’s headwaters, to transport water to Duck Creek. This
could be accomplished at a cost of about $750,000 - $1,000,000. Alternatively,
a pipeline could be created to transport water to Duck Creek from the
nearby Dredge Lake. This pipe would cost only about $96,000, but can
only be built if the diversion of flow would result in no detrimental
effect to the lake. If this can be shown, this choice becomes the preferred
alternative (Koski and Lorenz, 1999).
Sedimentation (4.2.2)
Sedimentation becomes a problem in streams which do not have the energy
necessary to flush their channel of sediments. In Duck Creek, poorly
placed culverts exacerbate this problem by damming the stream during
times of high flow, which allows sediments which would otherwise have
been flushed from the stream to settle and build up. The problems associated
with sedimentation are similar to those associated with the buildup
of iron flocculate: by filling in gaps in gravel along the streambed
with finer sediments, salmon spawning habitat, as well as insect and
invertebrate habitat are destroyed (Kohler and Soluk, 1997).
Non-point source pollution (4.2.3)
Non-point source pollution is the most significant aspect of urban runoff,
which, in turn, is the leading cause of stream impairment in the state
of Alaska. The Alaska Department of Environmental Conservation lists
30 streams as impaired by urban non-point runoff, including Duck Creek
(ADEC, 1996). Non-point source pollution is a diffuse type of pollution,
not associated with a single, discernible point of entry into the water.
Urban pollution is unique in that it consists mainly of non-point source
pollution (WDEQ, 1999). Non-point source pollution is not associated
with a single point of entry to the water because the sources are often
transient, such as motor vehicles. Motor vehicles release oil, antifreeze,
brake fluid, gasoline, brake pad dust, and other compounds into the
streams of the Mendenhall Valley when these compounds are leaked onto
roadways which drain into waterways of the area.
Other contributors to this phenomenon in the Mendenhall Watershed are
the chemicals used to clear roadways of snow, dirt and chemicals released
during contruction operations, chemicals, especially used automotive
fluids such as motor oil or antifreeze dumped into waterways by individuals,
and chemicals used for landscaping or purposes around the home. Chemical
compounds comonly associated with non-point source pollution include:
zinc, lead, copper, assorted hydrocarbons, nitrogen and phosphorus.
Bioaccumulation of some of these elements can make them particularly
hazardous to humans.
Because it has no defined point of entry into the waterway, non-point
source pollution requires a unique method of control. Point-source pollution
can typically be treated, but for non-point source pollution treatment
is not feasible. Rather, control of this phenomenon should focus on
minimizing the introduction of these pollutants. This is best accomplished
in different ways, depending upon the source of pollution. The following
sections discuss specific types of non-point source pollution.
Snow and Ice Control
Wintertime snows in Juneau can be heavy, and icing is common on Juneau
roadways during the winter months. To make driving conditions safer,
the Alaska Department of Transportation, as well as the City and Borough
of Juneau, plow roads and spread chemicals and sand to melt snow or
improve traction. In a conversation with local naturalist Richard Carstensen,
it was noted that the plow crews commonly plow chemical-laden snow into
the Duck Creek channel during the winter. Even if snow is plowed elsewhere,
when it melts in the spring, chemicals and sand leach into the surrounding
area, eventually finding their way into streams and contributing to
non-point source pollution. Sand applied for snow control contributes
to sedimentation, which is already a leading cause of damage to Duck
and Jordan Creeks.
The problem with the current snow and ice removal plan is that it is
enacted only after a snowfall, and after ice molecules have bonded to
the pavement. This necessitates an immense application of chemicals
or sand to make driving conditions safe. For protection of the stream
ecosystem, it is desirable to develop a snow and ice removal plan which
minimizes the usage of chemicals and sand. Test studies in Colorado,
Iowa, Oregon, Washington, and Kansas have shown that by applying a brine
of sodium chloride, calcium chloride, or magnesium chloride to the road
surface prior to icing conditions, driving conditions can be improved
over those obtained by post-snowfall treatment. This also cuts the amount
of chemicals necessary in about half (Oregon DOT, 1996). Not only does
this result in less environmental damage, but it drastically reduces
the cost of chemical treatment and may also reduce corrosion damage
to cars and dispensing vehicles. Snow-control crews are beginning to
apply a larger grain of sediment to the road for traction improvement.
A pea gravel sized grain would do far less damage to urban creeks than
sand sized grains (K Koski, pers. comm.).
Landscaping Chemicals
Landscaping in Juneau for private homeowners generally consists of a
grassy lawn, which often requires the annual application of fertilizing
chemicals for growing success. For many homes, excess chemicals flow
into the stormwater system, which is treated locally at the Mendenhall
Wastewater Processing Plant. Other stormwater systems flow directly
into the Mendenhall River or Duck Creek. For homes bordering a waterway,
excess chemicals will run directly into that waterway. In the waterway,
chemicals in fertilizing compounds are toxic to animal life and can
contribute to eutrophication. Generally preferable to this type of landscaping
is bioengineered landscaping which uses native species suited to the
natural conditions of the watershed to both reduce the necessity of
application of landscaping chemicals and improve aesthetic appeal. Also,
by using bioengineered landscaping, the protective quality of riparian
vegetation can be improved for any number of purposes, discussed in
the section on riparian vegetation.
Chemical dumping by individuals
Dumping of toxic chemicals into waterways is not uncommon in the Mendenhall
Watershed. Unfortunately, there is no way to tell just how often this
occurs. The City and Borough of Juneau offers periodic hazardous waste
disposal programs, intended to reduce this type of pollution. Probably
the best way to reduce individual dumping is to increase public awareness
of the disposal clinics and the environmental problems associated with
dumping chemicals directly into waterways.
Stream channel modifications (4.3)
Duck Creek (4.3.1)
Past stream channel modifications in Duck Creek have included placement
of culverts and the dredging of the streambed for gravel. In areas where
this dredging occurred, there remain to this day wide, shallow, slow
flowing ponds which have been identified as extremely damaging to the
stream. When a waterway is widened to the extent Duck Creek was, water
flow slows down so much that the stream loses enough kinetic energy
to drop its sediment load, leading to sedimentation, changes in temperature,
and an inability to support fish life (Koski and Lorenz, 1999). Dredging
also destroys the habitat around the stream, often leaving no riparian
vegetation. When the stream’s natural course is altered, the velocity
and flow are affected.
Poorly designed and placed culverts are perhaps the most damaging feature
added to Duck Creek during the development of its banks. At least ten
culverts have been identified in the stream channel which serve more
to restrict the flow of water than to facilitate it. During low flow
periods, these culverts often completely cut the stream off from itself,
and during floods they act as dams to slow the flow of water and cause
it to drop sediment it would otherwise have cleared from the stream
channel (K Koski, pers. comm.).
Poorly placed culverts make it difficult for fish to negotiate the
stream channel, and contribute to the mass dieoffs seen annually in
Duck Creek (Figure 4) (K Koski,
pers comm.). In nearly every observed problem with Duck Creek, poorly
placed culverts are at least a contributing factor, if not the sole
cause. Fortunately, new technology allows for the use of bottomless
arch culverts, which maintain the natural streambed while still supporting
the stream crossing. When only a pedestrian crossing is necessary, wooden
footbridges are preferable to culverts. Either type of crossing would
serve to alleviate or eliminate the problems associated with culverts,
which is imperative for the rehabilitation of Duck Creek (Koski and
Lorenz, 1999).
The culvert replacement effort would have an added bonus for residents
along the banks of Duck Creek. Because the poorly placed culverts act
as a small dam, slowing the flow of the creek, they also serve to cause
flooding at times when a natural stream channel would not flood. The
replacement of these culverts would reduce flood risk, reducing repair
costs and insurance premiums to those people living alongside the stream
(Koski and Lorenz, 1999).
Mendenhall River (4.3.2)
The Mendenhall River discharges an average of 1200 cubic feet per second
of water, much greater than any other waterway in the watershed. Because
it has more kinetic energy than other waterways in the watershed, the
river has potential for a higher rate of erosion than the other waterways.
The banks of the Mendenhall River can be divided into two types: low
shear and high shear, with low shear areas able to support vegetation
(InterFluve, 1999).
Many of the developed areas along the eastern bank of the river are
in high shear zones, and so private property is at risk to be lost through
erosion. Historically, landowners interested in countering this erosion
have armored their banks with stone riprap. This practice affects the
hydrology of the river in such a way as to cause increased erosion at
other points along the bank of the river, is generally thought to be
unaesthetic, and destroys fish habitat. This is one of the leading causes
of decreasing fish populations in the Mendenhall River (InterFluve,
1999).
Bioengineered bank stabilization programs can alleviate many of the
problems associated with riprap. Bioengineered bank stabilization techniques
combine the stabilization of a bank with the growth of riparian vegetation.
Whereas riprap serves to increase the velocity of a stream by reducing
friction against the banks, bioengineered stabilization techniques serve
to slow the flow of the stream, reducing erosion both at the protected
region and downstream. Bioengineered stabilization also provides cover
and areas of slow flow for rearing and migrating fish, which would serve
to reverse the trend toward reducing salmon runs in the Mendenhall River.
Private landowners who decide to develop bioengineered bank stabilization
on their property may be eligible for up to 75% reimbursement through
a variety of governmental sources, including the Wildlife Habitat Incentive
Program andthe EPA’s Five-Star Restoration Program (InterFluve,
1999). This is the best way for landowners to protect their property
and the environment at the same time.
Expected changes in flow (4.4)
A graph of the yearly averages of water flow in the Mendenhall River
since 1965 (Figure 5) reveals that
the river cycles between periods of low flow and high flow. These cycles
occur every 5-7 years, with the most recent low-flow year being 1998.
These estimates would mean that, at present, the river is in the beginning
of a high-flow phase. This cycle is most likely indicative of an overall
precipitation oscillation in the watershed, since any significant change
in flow patterns would probably not reverse itself so regularly. The
oscillation means that in coming years as the rehabilitation of local
watersheds and streams begins, the low-flow problem will be exacerbated.
This change likely only has a significant effect in areas such as Duck
Creek where low-flow problems often prove fatal to salmon.
A computer-generated trend line shows that the average flow of the Mendenhall
River in cubic feet per second is slowly increasing. This could be due
to an increase in total drainage in the watershed, which would be beneficial
to streams with low-flow problems, or a shift in the dynamics of the
watershed which cause more water to be diverted from small tributaries
to the Mendenhall River. This second possibility would further exacerbate
low-flow problems in the small tributaries. More studies are needed
to definitively determine the cause of this increase in flow.
Urban development (5)
Impervious cover (5.1)
The issue of impervious cover arises because it is a general indicator
of watershed health. When wild land is developed, much is paved or built
upon. When either of these occur, the developed land can no longer absorb
water, and precipitation or other water flows immediately and quickly
off the area, rather than the slow process which occurs naturally. This
natural process also filters the water, removing many impurities and
pollutants before they can enter the area’s drainage stream. This
filtering action, too, is lost when land is developed. Also, the ground’s
new inability to hold water means that in times of high rainfall, the
water will move to its drainage stream more quickly, increasing the
likelihood of flood. In times of low rainfall, less groundwater is available,
and stream channels dry out more quickly. This phenomenon and its effects
are discussed more in depth in the hydrology section of this report.
The presence of impervious cover greatly contributes to non-point source
pollution. Impervious surfaces prevent this non-point source pollution
from percolating downward, where it would be naturally filtered by its
passage through the ground and roots. Thus, impervious cover exacerbates
the problem of non-point source pollution by allowing contaminants to
be swept directly into the draining waterway, unaltered. Once in the
water, the effects of the pollution depend on the specific compounds
present in the polluted water.
Percent of area in the Eastern Mendenhall Watershed covered with impervious
surfaces is shown in figure 6.
The rapid increase in impervious cover corresponds directly to the rapid
increase in population in the watershed. This figure is not likely to
continue its rapid rate of increase, though, since much of the remaining
land is poorly suited for residential construction, or protected by
state or federal law. The current level of impervious surface in the
Eastern Mendenhall Watershed is 32%, greater than the figure of 15%
which generally indicates a rapid decline in watershed health (Water
Resources Agency, 1998).
Reducing the effects of impervious cover is generally more feasible
than reducing the amount of impervious cover itself. Native woody plants,
which hold the soil and water better than grasses, can help toward this
end. Willow and alder are favored because they offer the benefits of
woody vegetation and grow very quickly (K Koski, pers. comm.). Bioengineered
landscaping offers benefits toward negating the effects of impervious
cover.
Recreational uses (5.2)
The natural resources of the Mendenhall Watershed are a favorite recreational
destination for local and visitor alike. The Mendenhall Wetlands Game
Refuge is popular for walking, hunting and bird watching, and the Mendenhall
Glacier Recreational Zone boasts over 100,000 visitors annually. Tour
operators run rafts down the Mendenhall River. Local hikers make frequent
trips up adjacent mountains. The aesthetic appeal of the watershed is
undeniable. These recreational activities generally have little environmental
impact, and contribute greatly to the tourism economy of Juneau. The
financial benefits of maintaining the beauty of the watershed are one
reason to maintain that beauty. The social importance of the watershed
is another. It contributes greatly to the community identity of Juneau.
Impacts of population increases (5.3)
The growth of Juneau’s population has slowed greatly since the
population explosion in the sixties through eighties (Figure
2). If the historical trend holds true, the growth of Juneau’s
population will continue to slow for the next fifty years. Still, the
growing population will require land to expand upon. The City and Borough
of Juneau currently holds land in the western Mendenhall Watershed slated
for future development. That development will inevitably result in the
loss of some wetlands habitat, but the ever expanding body of environmental
knowledge and growing awareness of the environment will help reduce
the environmental footprint of that growth.
Management Plan (6)
Summary (6.1)
The Mendenhall Watershed has been adversely impacted by the rapid development
which took place there between the 1960s and 1980s. Duck Creek, in particular,
has been devastated by short-sighted use and modifications made to its
channel. The watershed is still useful as fish and wildlife habitat
and retains much of its natural beauty. The social and economic value
of these resources to the city of Juneau is great. Protection of this
value must be a top priority to managers and denizens of the watershed.
Development of the banks of the Mendenhall River has necessitated the
stabilization of those banks. The riprap protection used reduces the
river’s aethetic quality, its viability as a migratory coridor
for fish, and the stability of other points on the bank. Bioengineered
stabilization can help solve the stabilization problem Modern technology
and environmental science allows for the restoration of the watershed’s
health without heavily impacting human development in the area. Compliance
with best management practices will ensure that the watershed remains
a proud posession of the CBJ well into the future.
Mandates (6.2)
To improve the health of the Mendenhall Watershed, the detrimental modifications
made to the channels of Duck Creek and theMendenhall River must be reversed,
which includes replacing the perched culverts with bottomless arches
and reducing the width of the ponds which were dredged for gravel. The
new bank area should be converted to boggy marshes to mitigate the impacts
of iron flocculate and to filter pollutants from runoff flowing into
the Creek. Repairing the Mendenhall River should concentrate on replacing
stone riprap with bioengineered banks to stabilize the bank and reduce
erosion downstream. To provide incentive to property owners to use this
type of stabilization, the CBJ should inform property owners of the
federal programs which will provide up to 75% reimbursement.
The main regulatory change necessary in the watershed is an increase
in the required setback for development from the current 50 feet to
100 feet. This will ensure that future development does not harm the
streams which are currently less developed, such as Jordan and Montana
Creeks. This will also provide a healthy riparian habitat to filter
pollutants and provide fish habitat.
For long-term management of the watershed, it will be necessary to understand
the cause of the gradual increase in the flow of the Mendenhall River
so that management decisions can be made with a full understanding of
the factors which affect the watershed.
To reduce the sedimentation problems in the watershed and reduce the
quantity of chemicals introduced to the streams, the City and State
Departments of Transportation should replace their current post-icing
treatments with a pre-icing treatment program.
Funding and enforcement (6.3)
Responsibility for the protection of the watershed will fall ultimately
to the private citizen. The governmental organizations with authority
to direct the use of parts of the watershed have a very large say in
determining how that citizen will use the watershed, though. The main
tool for this management is the permitting process. By issuing permits
on a conditional basis or attaching conditions to title transfers, private
property can gradually be brought into compliance with the mandates
of this plan. Funding for these changes comes from the landowner. The
gradual nature of this process means that a fifty-year time frame for
the management plan is entirely appropriate. Because the waterways of
the watershed are owned by the City and Borough of Juneau (CBJ), the
CBJ can authorize in-stream restoration projects. The myriad funding
sources currently contributing to the restoration of the watershed should
be augmented by funding from the city and state levels. Infrastructure
projects such as the culvert replacements are also the responsibility
of governmental bodies. A prime example of the cooperation between private
organizations and government bodies are the current renovations being
made to Duck Creek, which are being organized by the Mendenhall Watershed
Partnership and funded mainly by the U.S. Army Corps of Engineers.
References (7)
ADEC (Alaska Department of Environmental Conservation.) 1996. Alaska
Water Quality Assesment: Section 305 (b) report to the U.S. Environmental
Agency. ADEC, Juneau,Alaska.
ADF& G (Alaska Dept. of Fish and Game). 1997. Mendenhall Wetlands
Game Refuge. http://www.state.ak.us/adfg/wildlife/region1/refuge1/mendenha.htm.
Accessed 11/23/00.
Barnwell and Boning. 1968. Water Resources and Surficial Geology of
the Mendenhall Watershed, Alaska: USGS Hydrologic Investigations Atlas
HA-259.
Beliharz. 1998. Duck Creek Hydrology Baseline Conditions. United States
Environmental Protection Agency. ADEC. National Marine Fisheries Service.
Auke Bay Laboratory. Juneau, Alaska.
Carstensen. 1999. Juneau Schools Water Watch. Discovery Foundation.
City and Borough of Juneau. 1999. Population Growth Boroughwide in Mendenhall
Valley and Lemon Creek Area. Community Development Department.
InterFluve, Inc. 1999. Guidelines for Bank Stabilization on the Mendenhall
River. ADF&G. Habitat Restoration Division, Technical Report 99-3.
Jones and Stokes Assoc. Inc. 1991. SE Alaska sportfishing economic study.
Final Research Report. December 1991. Sacramento, CA. Prepared for ADF&G,
Sportfish Division, Research and Tehnical Section , Anchorage, Alaska.
Kohler and Soluk. 1997. Effects of Sedimentation of Stream Communities.
Center for Aquatic Ecology. Illinois Natural History Survey. Illinois
Department of Natural Resources.
Koski and Lorenz. 1999. Duck Creek Watershed Management Plan. Duck Creek
Advisory Group. National Marine Fisheries Service. Auke Bay Laboratory.
Juneau, Alaska.
Muhlberg and Moore. 1998. Steambank Revegetation and Protection - A
Guide for Alaska. ADF&G, Technical Report No. 98-03.
Oregon DOT. 1996. Saving Money and the Environment. Roadsavers. Strategic
Highway Research Program. U.S. DOT. http://www.fhwa.dot.gov/winter/roadsvr/CS092.htm
Accessed 11/15/00.
USGS. 1965-2000 (provisional). Water Resources Data for Alaska. United
States Department of the Interior. Geological Survey.
Resource Data, Inc. 2000. Geographic, Land Use, and Environmental Data-
Mendenhall Watershed and Auke Lake area in Juneau, Alaska. Mendenhall
Watershed Partnership.
Stahl. 1999. Assessing the Feasability of Using Riparian Plants to Prevent
Fe-floc Formation in Streams. Project Final Report. University of Alaska
Southeast. Juneau, Alaska.
Water Resources Agency. 1998. The Christina Basin Impervious Cover Controls.
University of Delaware.
WDEQ (Wyoming Department of Environmental Quality). 1999. Urban Best
Management Practices for Nonpoinr Source Pollution. Point and Nonpoint
Source Programs. Water Quality Division. WDEQ.
Sources (7.1)
Carstensen, Richard. Personal communications. December 2000. Discovery
Foundation. (907)789-2319
Koski, K Personal communication. November 2000. National Marine Fisheries
Service. Auke Bay Laboratory. (907) 789-6024.
2001
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