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:
Juneau-Douglas High School
10016 Crazy Horse Dr.
Juneau, Alaska 99801
Table of Contents
Introduction (2)Definition of the watershed (2.1)
Statement of purpose (2.2)
Salmon in the watershed (3.1)
Other wetlands (3.3)
Riparian vegetation (4.1)
Water quality (4.2)
Expected changes in flow (4.4)
Impervious cover (5.1)
Recreational use (5.2)
Management plan (6)
Funding and enforcement (6.2)
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 dont 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 rivers 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.
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 watersheds 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).
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.
Governments 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.
The Mendenhall Watershed provides essential habitat for several species of salmonids (i.e. salmon and trout). Juneaus 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).
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 watersheds 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.).
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.
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).
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.
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 Creeks 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 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 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 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.
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 streams 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).
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 EPAs Five-Star Restoration Program (InterFluve, 1999). This is the best way for landowners to protect their property and the environment at the same time.
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.
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 areas drainage stream. This filtering action, too, is lost when land is developed. Also, the grounds 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.
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.
The growth of Juneaus population has slowed greatly since the population explosion in the sixties through eighties (Figure 2). If the historical trend holds true, the growth of Juneaus 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.
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 rivers 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 watersheds 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.
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.
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.
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.
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