Great Marsh Catwalk Project
In an effort to promote environmental educational opportunities at Marshlands it was obvious that the ability to circumnavigate the marsh would be very desirable. Improved access to deer hunting areas was not lost on the builders of the catwalk either! Prior to the catwalk the only option was to canoe down the middle of the marsh via Marsh creek and low water combined with overhanging Marsh Rose was a deterrent. There are walkable trails on either side of the marsh but no way to cross the lower marsh so as to connect these trails.
The marsh necks down to it's narrowest point at the Southeast boundary of the property where it is approximately 500' wide (see aerial photo). However, this section is virtually impassable due to dense Marsh Rose and 2-3' of muck. Then there is still Marsh Creek to cross which is about 20' wide at this point and approximately 6' deep consisting of water tapering off to increasingly dense muck! A bridge across Marsh creek with a cleared path through the Marsh Rose seemed like a temporary solution at best since regular clearing would be necessary and the you would still need hip boots to negotiate that path to any bridge across the creek. So the idea of a catwalk took hold and after doing a preliminary cost estimate (Total cost: $1,372 for lumber and fasteners). I decided to proceed knowing what it would cost but with only a vague estimate of the labor involved.
The basic design consists of support piers made with 4'x4' uprights and 2'x4' cross members spaced approximately 10' apart. The planking consists of 2'x10' rough cut White Oak. The White Oak is preferable to Red or Black Oak due to its closed cell nature and lasts well without any additional treatment for this type of service (exposed to the elements but not in earth or water). The piers were constructed entirely of pressure treated lumber.
The support piers were pre-fabed and delivered to the site with each numbered to match the intended position along the cleared path. In order to determine the length of the pier support posts the marsh was profiled with a steel rod every 10' to measure the depth to firm bottom (clay). The marsh was found to have a fairly consistent layer of gray clay below the muck which provides a firm footing for the piers. The chart below shows the measured profile and the plan was to sink the piers to that level across the span of the catwalk. Note the very consistent depth between the 200' mark and Marsh Creek. It is presumed that this might be the area that the creek meandered over during last millennium.
The actual installation was an evolutionary process. Initially the plan was to secure the planks with 20d nails. We quickly switched to deck screws so as leave open the option of flipping the planks if they should warp excessively since they are green lumber. Early on we also noticed that we better add some cross bracing between piers lest the whole affair collapse like a row of dominoes! Fore and aft cross bracing was added to every fifth span.
The summer being very dry there was little surface water so the post hole digging was slow but steady. Then the rains came and we quickly realized that digging post holes with about a foot of water on top was going to be a losing proposition! This problem was solved by a slight redesign of the piers to make them "self inserting" making post holes unnecessary. An electric winch was used to drag out the Marsh Rose root masses in the area that a pier was to be placed. With this system the operation speeded up considerably and the golden deck screw was driven Nov 4, 2002.
Here is a rough chronology of the project with links to details for those interested:
Thanks to Dan Glick (secured and delivered the oak planking) Steve Hunter (loaned some very useful tools), Pete Wolf, Val Shukaitis, Rick Kivela, Jamie Theurkauf, Bill Moore, Kirk & Jake Ewing (for carrying a lot of heavy lumber with 10" of foot room!), and Jeff Moore, my first assistant.