|Yukon/Tanana Rivers Drainage System (cite: AKFWS)|
Recently, one of the tributaries to the Tanana River has come into some trouble. The going theory is that someone dumped their aquarium into the Chena Slough near the town of North Pole. The aquarium's fish surely died, if there were any, but the pretty plants it contained have taken over several miles of a slow-moving stream. Eradication efforts are underway to remove this invasive weed and restore flow to the Chena Slough. (See local newspaper article)
So far, these eradication efforts have revolved simply around pulling the weeds. This makes for great "photo-ops" but does little for removing the fast-growing weed. Recently it has been proposed to step the efforts up a notch by applying an aquatic herbicide, Fluridone, to the Chena Slough. Fluridone, the company salesman from Indiana tells us, is harmless to humans and [$600,000 worth of chemical...] should be very effective at removing trouble weeds from our local waterways.
|Picture from Fairbanks Daily News-Miner|
In this series, we will look at the issues surrounding the invasive weed, locally referred to as "Elodea," and then take a look at a dysfunctional waterway that possibly needs some human intervention.
PART 1 - The Water
According to most definitions, a "slough" (/slou, slo͞o/) is a swamp, or a river running through a swamp. To early travelers that arrived in Alaska by steamboat or on foot, the vast, mosquito-filled land seemed like a giant swamp and the flood channels that cut through the dense forest were labeled as sloughs on early maps. Nearly every slough in Alaska begins and ends in the same river. A glance at a map of the Tanana River shows examples of many sloughs. The Alaska definition of a slough is, "a side channel of the main river."
|Figure 1. Tanana River Sloughs near Fairbanks, AK. Courtesy USGS|
In this 30 mile section of the Tanana River (figure 1), numerous sloughs are apparent, the bigger ones named. Most sloughs are navigable by boat at least part of the open-water season (May - October). The Chena River is a tributary to the Tanana River. Early explorers referred to the Chena River as Chena Slough. Until the 1970s, the lower 30 miles of the Chena River were dominated by waters entering via a slough that originated near Moose Creek, about 30 miles from what is now considered the mouth of the Chena River. After a massive, damaging flood in 1967, a flood channel and dike system were created that stopped the waters from the Tanana River from entering the Chena River via Chena Slough.
The Upper End of Chena Slough
An aerial photo from 1938 shows the Chena Slough as it departs the Tanana River between the town of Salcha and Eielson Air Force Base. The Chena Slough flowed swiftly through what is now the town of North Pole and residential areas along Badger Road. Most local residents refer to the Chena Slough as "Badger Slough." In 1938, the Chena Slough was further fed by waters from Moose Creek and French Creek. The Chena Slough was historically used by native Athabaskans as a travel route between the Tanana River and the hills surrounding the Chena River. Early explorers to the region used the Chena Slough as a portage around shallow rapids on the Tanana, often guided by local Athabaskans who knew the many channels and dangers of the Chena Slough.
|Figure 2. 1938 Aerial View of Moose Creek Area. Courtesy Fairbanks North Star Borough Archives|
|Figure 3. 2012 Aerial View of Moose Creek Area. Courtesy Fairbanks North Star Borough Archives|
|Figure 4. Infographic of the Chena Lakes Flood Project. Courtesy Army Corps of Engineers|
The Lower End of Chena Slough
Historically, the Chena Slough ran from the Tanana River through low-lying lands of spruce and birch forests for approximately 30 miles until it joined the Chena River about 3 miles downstream of where Nordale Road bridge is located today. To early inhabitants and explorers, this would have been considered the mouth of the Chena River. The waters of the Chena River run clear to brownish, compared to the gray glacial silt waters of the Tanana River and the original Chena Slough.
A comparison of the landscape at the mouth of the Chena River as seen in 1938 to that of today shows a remarkable transformation.
|Figure 5. 1938: Mouth of the Chena River at Chena Slough. Courtesy FNSB Archives|
|Figure 6. 2014: Mouth of the Chena River at Chena Slough. Courtesy Google Maps|
The New Chena Slough
Not really a slough at all, anymore, the Chena Slough contains ground water that seeps in through natural springs and underground aquifers in the area. The Chena Slough has gradually become little more than a swampy ditch in its upper stretches, completely choked by native weeds. Road crossings, bridges and culverts restrict the flow further. A project to replace small culverts to improve flow was completed in 2013 with few results. The main problem with the Chena Slough is that it has no headwaters. It is forever destined to become the "Chena Seep."
The US Geological Society defines a seepage as:
seepage--(1) The slow movement of water through small cracks, pores, Interstices, etc., of a material into or out of a body of surface or subsurface water.
Or possibly the "Chena Stream," although it may be a partial canal due to its heavily engineered design.
stream--a general term for a body of flowing water; natural water course containing water at least part of the year. In hydrology, it is generally applied to the water flowing in a natural channel as distinct from a canal.
These terms more clearly define the Chena Slough. Hundreds of drinking wells lie within yards of the Chena Slough. Many people irrigate gardens and lawns. Moose live their entire lives within the riparian habitat along the Chena Slough and are harvested by local residents for food. Many people eat fish caught in Chena Slough. Thousands of ducks use the Chena Slough as a nesting area. The Chena Slough is now a groundwater seepage stream, only a small portion of which is navigable by any type of boat.
The Future of the Chena Slough
With the completion of the Chena Lakes Flood Project in 1981, residents of the area gave up a navigable channel of the Tanana River in return for thousands of acres of land that could now be used for housing, and gained insurance that yearly floods would no longer be a threat to the town of Fairbanks (Figure 7).
|Figure 7. 1968 Flood.|
The Elodea infestation was first discovered in 2010 about 3 miles upstream from the mouth of the Chena Slough near the bridge on Repp Road. Someone presumably discarded an imported aquarium plant. Since then, the slough below that point has become increasingly filled with elodea. However, upstream from this point, the slough is completely choked with native weeds. In some areas, with no invasive species of aquatic vegetation, the slough appears as if one could walk across it.
If Elodea had never been introduced, the Chena Slough would still be in a death spiral. Silt that had been deposited centuries ago settles into the slow-moving seepage. Aquatic vegetation of any kind finds this an inviting place to grow. The entire Chena Slough was probably floatable by canoe for only a few years after it was separated from the Tanana River. Beavers and human bridge builders continually chipped away at the flow of the Chena Slough until numerous restrictions turned many sections into a more pond-like ecosystem.
Even if every bridge were removed, and every single plant was eradicated, the Chena Slough would not be navigable, nor would it ever return to its former status as a free-running slough. It is not a slough, and no one should expect it to behave as one.
In addition to the elodea infestation in the Chena Slough, this invasive weed is also seen in Chena Lakes. Chena Lakes is actually just one lake, built as a gravel pit for the Chena Lakes Flood Control Project. The gravel pit has since filled in with ground and rain water and is used as a local recreation spot.
|Figure 8. Chena Lakes Site, 1938. Courtesy FNSB|
|Figure 9. Chena Lakes, 2012 (FNSB)|
In part two of this series, we'll explore the weeds involved. In part 3 we'll discuss eradication methods and look at a report written for the Fairbanks Soil and Water Conservation District in 2013 entitled, "Chena Slough Hydrologic and Hydraulic Analysis for Existing Conditions and Channel Modifications." This report outlines numerous methods for improving the flow of the Chena Slough and holds the key to why Fluridone herbicide is not the right answer. Part 4 will outline a plan for the future of the Chena Slough that does not involve chemicals and an unsustainable management plan.