Sat., July 15: Monadnock Trails Week on Marlboro Trail

This day was part of Monadnock Trails Week as sponsored by SPNHF. They have held 17 MTWs so far. This day made 5 since the latest downpour, and Sunday had another 1.2" forecast for there.

This year the SPNHF coordinator Dylan sent me to Marlboro Trail. We hiked up over about 150 yards of pavers about 3'W (some split from the roundish glacial till that abounds there), a staircase of about 30 rocks ditto and with a rise of 8"-10", and many older rock waterbars in the 3-yard wide trail that all have failed and need cleaning now.

Our jobsite was about 0.5 miles up, on a moderate grade, a gully about 1' deep in mineral soil. They are adding separate steps in there, gentle grade between steps. My job was to design and build a waterbar uphill of the gully to divert stormwater runoff.

I kept a rock of about 1000 lbs towards the left or uphill of the bar. I helped others dig up and move another rock about that size that they much wanted as a step, and they gave me smaller but 200 lb-ish blocky rocks. I dug a shallow trench across the trail at a 45 degree angle, then set the rocks in it starting with the upper one touching the big one. From there downhill they all fit tightly and support each other, and the last one is bedded in a hole on existing soil.

Lastly, I dug organic soil from the line of the ditch. That went atop the crushed rock a helper packed at the base of the rocks on the uphill side of them, that tends to keep water from eroding a way down and between rocks. Only then did I dig the ditch several inches from the upstream side of the bar, from the downstream end by sliding my shovel upstream through mineral soil and leaving a U-shape bottom to the ditch. The soil we packed against the uphill side of the rocks.

The outflow ditch ends at what may be called a level spreader downhill of the trail's edge, so no flow onto the trail if it is full of sediment. Water flowing from the ditch slows, drops its sediment there, and percolates down through forest duff down hill of the trail. The sediment will be sandy mineral soil from the trail uphill. it can be shoveled back onto the trail downhill of the waterbar.

This type of construction seemed fitting for the top of the gully, where the pitch is about 4 in 12 and we have to build something that may go a few years between cleanings. Lower bars you step over won't work in such places. These stones will not move when stepped on.

i plead GUILTY, Your Honor. I forgot to photograph this, but the day was 6 hrs old already, warm and muggy, the team leader was waiting, and refreshments were calling. Loudly. Repeatedly, and with feeling.

Mon 7/17. After forgetting the photos last Sat, I drove back there under sunny skies this morning. A crew was there working on adding more steps. The new waterbar and ditch were working exactly as planned, and trail below in the gully was much dryer for not being a stream bed. To be honest, I left my shovel in the truck and carried only a hiking pole. That made it much easier to resist the temptation to fix drainage problems. "Not our trail..."

- Craig Sanborn, CHVTC Trsilmaster