water table questions

I'm not sure this is the correct forum for this questions but I wasn't sure where else to put it. I need someone to explain something that is happening on my land and I have no idea who to ask or what to look up so I thought maybe someone here would have an idea/knowledge/experience to share.

We bought a small acreage with a creek which ran seasonally. Within 10 days of any rain storm it was dry again except for some ponding in a couple of places. We put in a shallow water damn, 8 inches high or so with a spillway to insure we didn't block flow downstream (although during dry times there was no flow at all) and when it rains water flows like the damn isn't there at all. Since we put the damn in we now have a permanent creek. As a matter of fact we haven't had rain for 80 days and yet our creek is still full and flowing over the damn at a trickle.

Honestly, we are kind of baffled by how this happened. How can an 8 inch damn create a permanent creek from one that was only seasonal before?

Second oddity ... we can literally see the line of moisture in the soil rising up the creek bank as time passes. There is a line where the soil is wet below and dry above and it has been climbing ever since the creek began retaining water. Is that normal? Are we raising the water table by capturing water and holding it? Is that even possible?

I'm not sure if the dam is raising the water table, I kind of tend to doubt it is. Water tables are huge features underground that I don't think a creek will have a major affect on, but I could be wrong. Now the wet/dry line in the soil on the creek bank that is climbing since it began retaining water, that I believe is capillary action. The soil is wicking water up from the water in the creek.

I dont think you have effcted the water table but I certainly think you have effected the immédiate area around the dam :-)

Well done  What are you going to plant to take advantage of the soils increaced humidity .

How about making a chain of these dams :-)


David

Yeah, I think you just increased water infiltration into the soil.

If water was ponding before in certain spots of the creek, I would guess that the creek bed is at least partially sealed in some spots. By putting in the dam, you're giving your soil a chance to soak up some of that water, and some more of that water that would have largely flowed over less well-sealed areas of the creek bed are given the chance to seep in.

I think, perhaps over time, you might increase the rate of recharge of the aquifer, but I don't think an 8-inch dam is going to be creating springs for you. Of course, I could be wrong. It has happened before.

As to David's suggestion about a chain of dams, I would suggest, if you can get small rectangular bales of hay, that you consider staking rows of them across your creek in a dam-like fashion. It will slow the water, trap sediment, and eventually form damlike formations through sediment deposition. I think you still need to consider a spillway, but conversely, I think that such a dam would be water permeable enough to just slow the flow, and if not, the area could be designed so that the tops of the bale dams each have the same level, such that as each section fills, the water tops the dam evenly, and flows over top of the whole thing in a thin sheet.

If you gauge the hydrology right, you might just end up with a series of cascading long pools on your stretch of what you will have turned into a year-round watercourse. This means more water, but if you plant the right trees, it also means lower water temperatures with a higher dissolved oxygen carrying capacity, and perhaps waterfalls of a few inches from one pool to the next, adding oxygen to the system as a whole.

Who is downstream from you? Have you had any comments or complaints, or really happy neighbours with increasingly useful land?

Congratulations. You seem to have done exactly the right thing to slow the water in the system. Some pics would be lovely, but keep it up, keep us posted, and good luck!

-CK

@chriskott Hay bales ... What a brilliant idea ... much simpler than lugging concrete bags or fiddling with metal sheeting, etc. I'll take pics and post them as we build it.

The beauty of where our land is, is that even though we have folks down stream from us, they probably won't notice anything from our now full time creek. Where it leaves our property, it runs under a road and joins a year-round stream on the other side and then runs along the side of a cattle pasture and into a ravine down a mile or so.

On the other hand our upstream neighbor might notice but hasn't said anything. Since he took a trackho and completely reshaped over 100' of the creek banks/beds without consulting the flood commission (read "no permit" ... "heavy fines") I doubt he will say anything either. But where we have our dam and are planning on the other ones, I haven't noticed much rise in his portion of the creek at all.

As for planting things to take advantage of the localized water ... hmmm, not sure yet. The creek is literally right through the middle of our woodlands and we planned to leave it mostly as a wildlife corridor but clearly if we have changed the local water levels it will benefit our food forest. We have black walnut trees on the creek which we were able to tap for syrup this year, but I don't want tons of black walnut because they are too hard to clean the nut meat from. We found a few blackberry bushes just off the creek so we created a thicket with some thornless varieties in the same area.

It is very likely that all the earthworks that your up stream neighbor did, has somehow moderated the highs and lows of the creek on your property.
maybe it a win-win for both of you, or maybe he has depleted his top soil but enriched the sub-soil which then empties out on your property. It might have taken a year for his earthwork to charge up the soil so maybe that is why there is a disconnect.

It is also possible that someone is pumping up alot of deep aquifer water, and charging the water table.

I was wondering if you possibly had any photos to share. I just put three experimental dams in two branches of a gully that runs through the portion of the woods that I want to develop into a zone 2 garden. Waiting on the next rain event to see how they hold. I will take some pics next time I head out there.

The basic aim of my design is exactly as described here; to slow the flow of water and the loss of valuable silt and organic debris. We laid branches on contour and stuffed the cracks with twigs, occasionally reinforcing with stone or with sticks pushed into the clay. One stone also acts as a sort of riprap to redirect current toward the dam so that the path of the water is approximately perpendicular to the dam.

We worked with extant trees to a large extent. Long term goal is to encourage ponding and plant a guild based around watercress and willow.

An interesting situation to find yourself in. I am interested in the final outcomes.