Hand-digging Vernal Pools in NJ (copied from main forum)

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cbernz
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Hand-digging Vernal Pools in NJ (copied from main forum)

Post by cbernz » November 22nd, 2013, 6:49 am

If you have the space, and you live in the right kind of area, building small vernal pools on your property can be a fun and satisfying project. I built my first one in the fall of 2011, after being inspired by this detailed PDF about vernal pond construction: http://herpcenter.ipfw.edu/Outreach/Ver ... dGuide.pdf There are many methods you can use to build vernal wetlands, but I discovered that I was able to build mine very simply with practically no specialized equipment. After 2 years, my pond is doing quite well, and I decided to build another larger one this fall, using the same easy method.

I live in Morris County, NJ, in a semi-rural area just south of Great Swamp NWR, the largest and best-known preserved area of the Passaic Meadows. The Meadows are the remnants of an ancient glacial lake, and include swamp, marsh, floodplain forest, bogs, and other habitats that are home to some pretty interesting herps, including a certain turtle and the southernmost population of Blue-spotted Salamanders. This whole area is full of vernal wetlands of all types, due to the high water table and frequent flooding. Here are some nearby "wild" vernals that I photographed this week:

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This is a small, fully shaded (surrounded by trees) vernal pool. We are having an exceptionally dry autumn, so it is totally waterless right now.

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Here's a larger, deeper, mostly shaded pool.

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This one is only partially shaded, and therefore has a greater diversity of grasses and other plants.

My property is on a quiet residential street that dead ends at the Passaic River on a small NWR parcel. From the street, my 2-acre yard slopes down towards a small red maple woodland drained by a small creek. The woodland extends in a narrow strip all the way up to the Passaic and to the Great Swamp. The site I chose for my first vernal pool is right where the lawn meets the woods. The first thing I did was dig several deep test holes to find out what my soil was like. I made them about 2.5 feet deep. The main thing you have to worry about with constructing a pond is water retention. If the soil is too loose or gravelly, you need to buy a liner, or use some elaborate construction techniques. What I found, to my delight, was that not only did I have some beautiful solid clay about 20 inches down, but my holes almost completely filled with water in a couple days, indicating a very high water table. This meant that all I really had to do was start digging, and as long as I dug deep enough, the pool would hold water for much or all of the year.

I don't have any photos of the construction process of this first pool, but I will go into more detail on the second one. Here is the pool as it appeared the day I finished it in November 2011:

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The hole is about 25 feet long and 15 feet wide at maximum, and 3 feet deep at the deepest end. I dug the entire thing myself, over the course of a couple weeks, using only a shovel, heavy duty pruning loppers, a small pruning saw, and a wheel barrow. The tarps are covering the fill dirt that I used to make a berm on two sides of the pool. Once I finished digging, I spread a couple inches of topsoil over the entire area, and then several inches of dead leaves over that.

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Here's what the pool looked like 3 days later, just from groundwater seeping in.

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After another 7 days and a few rainstorms, the pool was completely full of water. You can see that I added some branches and logs for cover and egg deposition sites for amphibians.

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This is what it looks like now, after 2 years. I've found quite a few amphibians and insects breeding in the pool over the past couple seasons:

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The first species I found in March, 2011, was this one, the newly described Leopard Frog whose name I don't know yet (does it have one?).

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This year I found this pair of Wood Frogs, so far the only vernal pool obligate species I've seen here.

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Wood Frog eggs.

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Northern Gray Treefrogs sang from the grass around the pool this May.

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Gray Treefrog tadpole. I had never seen one before. They hang from the surface looking just like little diseased leaves.

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My daughter holding one of the many Green Frogs that live in the pool.

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Great Blue Skimmer, one of several dragonfly species I've found breeding in the pool.

I'm very pleased so far with this vernal pool, and it's already a great little habitat, but of course the only thing better than one vernal pool in your yard is two, so this October I started digging a second one. I wanted the new one to be considerably larger than the first one, but also much shallower than the first, so that it would periodically dry out. My first pool, even in this drought, still has at least 18 inches of water.

Here is the bare site:

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It's just a few yards downslope of the first pool, which is basically hidden, just left of the bird house. The ground slopes gently downward from the background to the foreground, and also downward from right to left.

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Step one in the process is to dig out the top layer of soil. With the shovel method, this is by far the most tedious and difficult part of the project. Since the site is next to woods, this top 8-10 inches of soil is packed with tree roots, in addition to grass and grassroots. I started by digging a narrow trench (2 shovel widths) marking the perimeter of the pool, then cut out chunks of turf, soil, and roots using the spade and a pruning saw. Most sane people would probably just rent a bulldozer or steam shovel for this, but I had a lot of free time, I like manual labor, and I enjoy the feeling I get looking at something I built by hand.

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My daughter helping out. I dumped the wheelbarrows full of dirt at the downslope edge of the pool to form a berm that will help contain the pool during high water.

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Step 1 complete. The top layer of soil is gone, and you can see the low berm of soil along the back edge.

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Step 2. I decided where I wanted the deepest area of the pool to be, and dug a narrow trench to mark it off (visible in the center of the photo). Then I dug about 8-12 inches of soil out from this area, making a deep area about 12-16 inches below the level of the grass. Due to the slope of the terrain and the berm constructed at the back, this area will actually be somewhat deeper, because the water at the low end of the pond will rise a little above where the soil used to be.

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Step 2 mostly finished. The darker reddish-brown area is the freshly dug deep section. The berm has grown with the additional soil, and I've used the spade to slope the sides of the pool as naturally as I could.

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You can see the deepest parts of the pool after a brief rain. The very next day, these puddles were gone. The water table is pretty low right now, well below the deep end of the pool, but in a normal autumn, this whole pool would probably have 4-8 inches of water, at least.

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With the fallen leaves covering the whole site, it looks fairly natural. I'll try to post an update once the pool fills in and starts getting some action.

Over the past couple weeks, I've been going out every now and then to do a little soil sculpting: shaving down a couple of the sides, making the deep end slightly deeper, taking off a bit more of the grass layer, and tamping down the soil on the berm by walking back and forth on it. Several times already, I've decided the digging is done, but since we continue to have this drought, and the soil is dry, I keep going out and digging some more. Just to give you an idea of the weather, our average rainfall for the months of October and November is about 8 inches, and we have only had about 1.25 inches. Not great for the environment, but fantastic for digging.

Once the digging is done, the only other concern is erosion control. With my first vernal, I used tarps over the exposed soil, and later seeded it with winter rye. My new pool is much broader and shallower, and I am less concerned about erosion. I'll probably compact the steepest areas with my feet, and maybe cover them with dead leaves. After the ground freezes, erosion won't be a problem at all until spring, at which point I can mulch or seed the areas of exposed soil. One of the advantages of the shovel method is that you only minimally disturb the soil, so there is far less loose dirt lying around than there would be if you used a bulldozer or other heavy equipment.

Anyway, this has been a fun ongoing project for me. I hope this post will be of use or interest to some of you. My method certainly won't work everywhere, but I hope I showed that building habitat on your property can be a fairly simple and rewarding experience. If you have the room, and if you can hear, find, or know of vernal pool breeding species in your area, I highly recommend trying to build a vernal pool.

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MarcLinsalata
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Re: Hand-digging Vernal Pools in NJ (copied from main forum)

Post by MarcLinsalata » November 22nd, 2013, 11:05 am

That's awesome!! :thumb:

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MattSullivan
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Re: Hand-digging Vernal Pools in NJ (copied from main forum)

Post by MattSullivan » November 22nd, 2013, 11:43 am

very awesome! wish i had the area to do this :/

sstaedtler
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Re: Hand-digging Vernal Pools in NJ (copied from main forum)

Post by sstaedtler » November 22nd, 2013, 11:50 am

Very cool. Thanks for sharing!

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incuhead2000
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Re: Hand-digging Vernal Pools in NJ (copied from main forum)

Post by incuhead2000 » November 22nd, 2013, 6:14 pm

This is a most excellent post! Way cooler than the littering I do to just attract snakes!

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cbernz
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Re: Hand-digging Vernal Pools in NJ (copied from main forum)

Post by cbernz » November 30th, 2013, 1:05 pm

So far, so good. The pool filled up nicely after a winter storm dumped almost 3 inches of rain:
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The deepest part of the pond was filled up to about 17 inches.

Here's what it looks like right now, frozen over:
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I spread wood chips over the exposed dirt to prevent erosion. When the ice thaws, I'll go back out and dump a whole bunch of dead leaves into the pond, to cover the bare mud at the bottom and provide nutrients and habitat for benthic organisms. I'll also dump in some logs and branches.

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