Design by Nature
A wetland is a lake’s best friend. Wetlands come in all shapes and sizes, including the transitional area between open water and dry land on the margin of lakes, rivers and streams. A healthy wetland next door will trap sediment, put the brakes on flood waters, and provide room and board for fish, fowl, furbearers and amphibians.
Sedimentation is a lake’s mortal enemy. Sedimentation occurs when soil erodes from the land that surrounds a lake or river (the watershed) and sinks to the bottom of the waterway. Erosion is a natural process, and sedimentation is an inevitable part of growing old for every lake, but human activity in the watershed that disturbs vegetation - amplified by easily erodible soil and steep slopes - can really speed things up.
When the sediment piles up, it can smother bottom dwellers along with important fish feeding and spawning areas. Too many nutrients deposited along with the soil can cause unsightly blooms of algae that use up oxygen and choke out other aquatic life. Shallow waterways make navigation tricky and create hazards for boaters.
The conventional approach to battling sedimentation problems has been to scoop out the sediment by dredging and move it to dry land. The classic suction dredge looks like a large barge and works like a vacuum cleaner, sucking up the sediment from the lake bottom and then pumping it through a pipeline to the dredge material relocation area on the lakeshore. Typically, the dredged material is allowed to dry until it’s ready to be used beneficially as clean fill for construction projects, or as a topper for farmland.
This tried-and-true method gets good results, but in some cases, wetter is better. When it comes to keeping our state park lakes sparkling clean and creating a happy home for aquatic critters, as well as a nice place for boaters, the folks at Ohio State Parks are taking their cues from nature and using wetlands to fend off sedimentation problems.
At Rocky Fork State Park, an especially stubborn sedimentation problem has been addressed with a high-performance, 90-acre ‘in-lake’ wetland built with a low-tech approach. A dozen years ago, Rocky Fork lake was dredged to deepen the navigation channel to 12 feet; six years later, the depth of the dredged area was a mere two feet. The lake had to be dredged again, but this time, the dredge material relocation area would be a wetland designed by nature.
A quiet cove where Rocky Fork Creek enters the lake was selected for the wetland makeover. First, a pair of “off set” earthen levees was constructed in the lake to retain the dredge material and to create a “backwater” effect would allow the velocity of the incoming water from Rocky Fork Creek to slow down and drop its sediment load. Next, the dredge material was pumped well upstream of the levees to create an underwater landscape of peaks and valleys. Then, a serpentine channel was cut through the newly deposited dredge material to provide access to the wetland area for shallow draft boaters while allowing water to meander through the wetland. The material removed from this cut was deposited to either side of the channel, creating hummocks rising above the water level to provide nesting and resting islands for waterfowl. Wetland plants from the neighboring lakeshore quickly invaded, and the seeds of emergent wetland plants lying dormant in the mucky soil soon sprouted, creating a smorgasbord of tasty morsels for an amazing assortment of waterfowl. In just a few years, the young wetland had become so rich and diverse that it attracted a small flock of roseate spoonbills - a coastal species seldom seen in Ohio - that had stopped to sample some Rocky Fork hospitality. Today, loons and bald eagles are regular visitors.
A proposed upcoming project at Rocky Fork to address ongoing sedimentation problems upstream in Clear Creek, which also empties into the lake north of the new wetland, illustrates the striking contrast between the current approach and the old-fashioned ways of doing business. A generation ago, well-meaning environmental stewards scooped sediment from the bottom of Clear Creek and placed it atop the stream banks, creating a dike along the stream channel. Since the built-up channel is not easily overtopped, floodwaters rush through the channel rather than spreading out over the adjoining floodplain, and dump even more sediment into the lake. An on-going Ecosystem Restoration Scoping Study in cooperation with the Army Corps of Engineers is considering removing all or part of the dike. The breaching of the dike would allow Clear Creek to reclaim its floodplain and deposit sediment before reaching the main body of the lake. The end result would be less sediment being deposited into the lake, and less dredging needed to maintain clean, safe, navigable waters.
The granddaddy of manmade in-lake wetlands in Ohio State Parks, Indian Lake’s Prairie Wall Wetland, is another example of a wonderfully successful wetland project that serves double duty as a habitat enhancer as well as a sedimentation solution. Today’s wetland harkens back to Indian Lake’s origins as a cluster of kettle lakes that formed in depressions left by the retreating Wisconsinan glacier about 13,000 years ago. Over the course of millennia, this assortment of small lakes matured into a shallow, marshy landscape covering more than 600 acres. In the 1850s, ambitious canal builders - who were probably unaware of the ecological value of this extensive natural wetland - dug in and around the morass to create a single island-studded reservoir to feed the nearby Miami and Erie Canal. Since the canal era, modern-day Indian Lake has required frequent dredging to remove sediment that has eroded from developing land, farm fields and stream banks.
About twenty years ago, when the time came to dredge navigation channels through a shallow lily-covered cove in the northeast part of Indian Lake known as the Game Reserve, local fishermen feared that the dredging operation would destroy fish habitat. They grew even more skeptical when an earthen dike, known as the Prairie Wall, was built in the lake beyond the Game Reserve, and the dredge material was pumped behind the Prairie Wall dike, creating the foundation of a 20-acre wetland. The fishermen’s fears quickly dissolved when the young Prairie Wall Wetland blossomed into a diverse and complex marsh reminiscent of the Everglades, providing a haven for waterfowl, and thriving nurseries for sport fish. Today, the wetland is rich with volunteer stands of buttonbush, arrowhead and marsh mallow, and is frequented by egrets, herons, bald eagles and cormorants. Sedimentation in Indian Lake has been reduced dramatically thanks to the work of the wetland, as well as the cooperation of neighbors who have participated in the Indian Lake Watershed Project since 1990 to keep the soil in its place with good land management practices in the watershed.
To date, more than 150 acres of wetlands have been created in Ohio State Park lakes using dredged sediment to create a wetland foundation and allowing nature to do the rest. With elegant simplicity, the problem becomes the solution to preventing future sedimentation problems - just like nature intended.