The Nature Conservancy: Big Woods Stream Restoration

Muddy Waters

Benson Creek lies within the Cache River Watershed in the Arkansas delta. The Cache and its main tributary Bayou DeView suffer from degraded water quality, characterized by elevated levels of nutrients, biocides, and (most noticeably) sediment.  According to locals, as recently as 50 years ago most of the low-gradient rivers and streams in eastern Arkansas still "ran clear... and (were) deeper and narrower as well."

New scientific evidence has shown that sediment and nutrient-laden waters not ony degrade habitat close to the source, but can affect downstream systems, sometimes hundreds of miles away. Degraded water quality in Arkansas has been shown to contribute to the second-largest zone of oxygen-depleted coastal waters in the world. Also known as the "dead zone," the hypoxic waters off the Louisiana coast (where the Mississippi River flows into the Gulf of Mexico) have more than doubled in size since 1984.

One of the main goals of this stream restoration is to serve as a demonstration site for water quality improvement within the Lower Mississippi River region. Our   monitoring plan includes installing and collecting data from a continuous sampling station located just downstream of our project area. This station, along with 6 others dispersed within the Cache watershed, is part of a larger study by The Nature Conservancy, in partnership with Arkansas Natural Resources Commission (ANRC), to understand the sources of elevated suspended sediment in the Cache River and Bayou DeView

 

Winter Break

As expected, work on the jobsite has stopped for the Winter, a time in Eastern Arkansas when seasonal rains flood streams and rivers and saturate the soil. Currently our stream restoration project is on schedule (half of the proposed channel has been excavated), and work will resume in the Spring with a completion date expected sometime this Summer.

    

Our Partners

Wolf Creek Charitable Foundation   

 

Erosion and Deposition

Complex topographic and depositional features are associated with the Mississippi River Alluvial Plain. All the features are due to erosion or deposition by the Mississippi and its tributaries except for loess, which was deposited by wind.

Erosion, sediment transport, and deposition can occur in relatively stable conditions are are natural processes essential to the dynamic stability of rivers and streams. When these processes become extreme or out of balance, erosion and transport become degradation (left) and deposition becomes aggradation (right).

Human modifications to the landscape strongly influence triggers to instability, accelerating the erosion potential and altering sediment transport and flow regimes of channels. See below: The Walla Walla River in December of 1964 defies an attempt at channelization and re-creates meanders, point bars, pools, and riffles.

Returning Equilibrium

Benson Slash Creek was once a wooded, meandering stream located in the heart of the great Mississippi River floodplain. Although there are no known historic photos or accounts of this particular drainage, we can speculate on what it used to look like. Our best guess is that Benson was narrow, relatively deep and gently meandered back and forth across its floodplain before it was channelized.

Before human intervention, it was probably what is referred to as a type "E channel". These biologically-rich streams are highly sensitive to changes in sediment and stream flow, and require thick riparian vegetation for channel stability. Benson Creek was systematically straightened, widened, and deepened over sixty years ago causing it to be in a state of disequilibrium (see channel evolution representation above).

By modeling our restoration design off of undisturbed streams in the region, we hope to return this once diverse ecosystem back to a functioning represenative of its original state. You can see below how the designed stream riffle and pool cross-sections closely resemble those from one of our reference sites. Note that the image on the bottom left depicts the channel in its current, altered condition.

   

Please visit EPA's WARSSS website for more information regarding technical tools for approaching impaired watersheds.

Delta Rivers Rising

The winter rains are upon us and work on the jobsite has slowed accordingly. "It's hard to run an excavator when the tracks keep slipping underneath of you every time you attempt to dig in," says ecologist and expert earth mover Matt Lindsey. "Every job out here is more demanding when it gets wet."

With over six inches of rain falling within the past three weeks, streams and rivers in the region have begun to swell and even overtop their banks. "Delays due to high water are expected with any project in this eco-region," according to Josh Duzan who has been with Arkansas' Nature Conservancy chapter for three years and has watched Delta rivers rise and fall with the changing seasons.

"If there's one thing we've learned over the years, it is that you can't win a footrace with Mother Nature." At some point within the coming weeks, construction will halt until the rainy season lets up. The hope is that Phases I and II of the project will be completed before that time comes.

   

Visit our Site

Benson Slash Creek is located in Eastern Arkansas, near the towns of Brinkley and Cotton Plant. If you or your organization would like to see our progress firsthand, please contact us:

Email Delta Ecologist Josh Duzan at jduzan@tnc.org                                              Delta Ecologist Matt Lindsey at mlindsey@tnc.org                                       Delta Program Director Roger Mangham at rmangham@tnc.org.

DRIVING DIRECTIONS:

• From Interstate 40, take the US-49 /AR-17 exit- Exit 216- toward Brinkley / Cotton Plant
• Turn LEFT onto N MAIN ST / US-49 / AR-17    (1.2 miles)
• Turn SLIGHT LEFT onto AR-17                           (5.1 miles)
• Turn RIGHT onto MILL RD                                   (0.6 miles)

You will see our sign on the NORTH side of Mill Road.

Biological Monitoring

The success or failure of this stream restoration depends on many factors, many of which are intangible and difficult to monitor. It can be effectively judged, however, based on how the affected ecosystem responds to our efforts. As with all of our restoration projects, we are monitoring the pre- and post-resoration site conditions in order to determine measures of success.

One aspect of our monitoring plan for Benson Slash Creek is instream biological sampling of fishes and macroinvertebrates (small 'bugs' including insect larvae, crustaceans, and mollusks). Following guidelines outlined in EPA's "Rapid Bio-Assessment Protocol," fish are stunned with a jolt of electricity applied from a backpack electrofisher. They are collected in a bucket, identified in the field, and subsequently released. Macroinvertebrates, on the other hand, are collected with D-frame nets and identified in the laboratory.

In addition, we have set up plant monitoring plots criss-crossing the floodplain and adjacent terraces of Benson Creek in order to monitor how the plant life responds to the site's new hydraulic regime. I am personally excited to watch the gradual change from agricultural field to bottomland hardwood forest.

Installation of Log Sills

Our filter fabric came in last week, allowing us to place log sills at pre-selected stations within our channel. A sill is simply a large hardwood log placed perpendicular to flow at a riffle within the stream. Large woody debris (LWD) naturally plays an important role in delta streams and rivers, helping to stabilize the bed and channel, as well as providing habitat for macroinvertebrates and shelter for various fishes. Our log sills are designed to mimic naturally occuring LWD and provide these vital aspects ensuring that our engineered stream acts as a healthy and stable ecosystem.

Below: the installation of a log sill. Note the black fabric placed upstream of the sill; this keeps water from flowing under the log, thereby compromising its structure. The entire process takes from 1 to 2 hours.