Killer of Chains
Hike/Bike Path in 5yr Floodplain?
I'm starting my first real trail organization/build/plan in my hometown, basically I heard about it by stumbling onto a website that mentioned wanting to connect two previous unconnected (officially) area. The areas were already connected via a 2 mile trail, but it was not recognized in the counties park system or bicycling trail map (for roadies). The county would like to connect these two areas (officially) by combining an offroad trail with on road trail through downtown Marietta.
I think this is a waste of a perfectly good and well used offroad trail below Marietta, however, that trail is often subject to flooding.
I have spoke with another woman who'd like to see this trail go into planning, as well as many others over the past 10 years who've wanted to see a Park to Park link that was all wooded.
However, the trail runs in these aforementioned floodplains, as well as property owned by a local farmer, Armstrong World Industries, and a local boat club. The trail would also need to address the high volumes of traffic that it would share a roadway with in order to cross a creek just outside of Marietta.
Is this something I should try to get some advice from IMBA on?
It never hurts to have the input from someone who has built trail in a flood plain...
The Hoosier Mt. Bike Assoc. has plenty of experience with this topic...
In fact, the most populated trail in the state (Town Run Park) is in the flood plain of the white river and has been in place and maintained for more than a decade now... And yes there are constant reroutes, but our local group does a great job keeping thousands of riders rolling along this "not-quite" 8 mile loop.
Town Run Trail Park Indy
I head up the trail work at Town Run. It is along the White River in Indianapolis.
Town Run was HMBA's first trail and has been a good learning experience for trail building, but any trail built in a flood plain will require higher than normal maintaince.
The biggest issue in a floodplain is obviosly flooding, This biggest issue we had with flooding is that the orginal trails were built be motorcycles and atvs in dry conditions. So the trails often went down to the river's edge. This ment that any little rise in the river level would come onto some part of the trail. It is important to make use of the national weather services Hydrology info. I think this is the page for your area
How high you build the trail is a trade off between milage and maintaince issues.
Here is the hydrology page nearest to Town Run Trail Park
The flood action stage is 7.5' and the flood stage is 11.0' feet. At 11 feet, channels of water flow through the park. It is not practical to build the trails at or above the 11 ft level.
The 7.5' level happens pretty often and trails this low end up with sand and debris after floods. The key at Town Run is the bridge that connects to sections of the trail. The water reaches this bridge at 9.5'. So we settled on the 9.5' river level as the standard for where the trail needed to stay above.
In the past 2 weeks, the the river has been above 7.5' 3 times, but has not gone above 9.5'
The easiest way to mark the low areas you want to stay out of is when the river is up. Look at the river level on the hydro page and then go put up flags along the edge of the water. Your action stage is 44', so if the river gets between 44' and 49' get out and put down flags. If you don't get high water, then you could use a clino to mark the 44' and 49' levels (two person job, one person with a pole to place at the edge of the river and one person to sight off of it).
The worst part about floods is that they generally happen days after the rain, so riders will come out on a sunny day not thinking about the heavy rain up stream in past days. If only a few sections are under water, they will ride and short cut the flooded area. Also, if you build close to the river bank you may have errosion pull down the bank and take trail with it. We close Town Run every time the river floods onto the trail, for the safey of riders but most importantly to protect the trail.
Many flood plain areas have levys. Levys allow you to build bench cut trail and often times the levys were built in the sweet spot for where the river often rises to. Be very careful about building trail below the old levys, as you are likely going into an area that will flood often.
No matter how high you build the trail, it will flood, but if you can keep riders off the trails until they dry, its pretty easy to walk the trail and clear the flood debris.
If you want to talk about flood plain trails, shoot me a PM and I will give you a call.
See, told ya Paintpeelin'...
Thanks Paul. You Rock!!!
Killer of Chains
Turns out there are two areas of concern that limit the ability to run the trail continously on dirt.
One is a small stream that empties into the river, and has 20' high banks on either side, and is mostly soft dirt that washes away easily. In order to cross the stream, you must walk up the embankment towards the railroad bed (still in use) and walk along the small 10' railroad bridge.
The other is an old dam that is 30' wide that you must either use a railroad bridge to cross or the highway.
It's a shame the project doesn't have more money, because the dam has trolley platforms that could be built across, and the small stream is just that...small.
Unfortunately, both area are within the flood plain. Ugh.
I'm hoping we may be able to make a dirt path on the opposite side of the rail tracks for about 2 blocks.