Civil engineering: or, how do I get rid of a moat in my yard?

Factual Questions
1

The missus and I purchased a “new” house last year, sitting on just over an acre of land. The house was built in 1954 on former farm land. The back yard slopes away from the foundation, dropping to about 30 inches lower in 50’ or so, then slopes back up to the rear property line (200+ feet away) until it is 18" lower than the foundation.

Shortly after we bought the house last year, it began to rain. Rain like you read about. Rain like I contemplated an ark (what’s a cubit?). The depression in the back yard, running the width of the yard, filled with water. For better than three weeks, I had an 18" deep moat seperating me and my dog from the rest of the yard. Talking to our new neighbors and the family we bought the house from, they said that the last time this happened was 1984. Ok, no big deal. Defication occurs.

Come September, same rains, same moat. Now I’m getting angry.

We’re having a contractor come in within the next few weeks to finish grading our septic system (installed at the time we bought the house and still unfinished - you can imagine my ire). He has seen the moat, and has a cunning plan to rid us forever of the water. He claims that he can dig a hole “to the aquifer,” by which I hope he means the water table, fill the hole with 3/4" gravel, and grade the yard above it. When we get the heavy rains, the water will drain through the gravel into the water table and disappear.

Herein lies my question. Is this going to work? My understanding of hydraulics says that the water is going to follow the path of least resistance, and giving it a nice big gravel tube to come up through will cause me to end up with an artesian well in the yard. I live in a very wet area, my two sump pumps didn’t stop cycling (literally) for 6 months. Started in August and ended three weeks ago. The water table comes out of the ground in the wet seasons, so wouldn’t I be setting myself up for permanent moating if I use this guy’s scheme?

This of course doesn’t take into effect the legality of such a scheme, for which I’m not concerned with here (I am concerned with it in reality, since where he wants to do this is in a wetlands buffer zone, and I don’t have a permit for that sort of work - only a septic grading).

In short, does this guy’s plan hold (or drain) water, or is he a crackpot with an excavator?

2

That is one way of doing it. . . however I’m not sure how deep your water table is.

I’m dealing with a similar problem in my current project: I have an alert fighter ramp which, when it rains, will generate a lot of runoff due to the size of the damn thing. I’m basically cutting “V-Ditches” alongside the ramp and backfilling it with ballast rock. The ballast will help prevent erosion of the ditch (by slowing down the water) and will provide a surface to walk/drive over. It’s ‘combat engineering’ but it works.

In your particular situation, he could do it vertically (sinking that hole) and filling it with gravel, or he could cut similar ditches horizontally and fill those with gravel too. I personally, would sink a hole and line it with some sort of pipe–PVC or iron–just for some extra stability, and then fill it with gravel.

Either way, it might not be the most elegant solution, but it oughtta work.

Tripler
Just go with the flow, man.

3

And in my “Hey-that-sounds-familiar”-based exuberance, I glazed over this part too quickly:

:smack:

This complicates things. I would see if he can horizontally duct the water away, and off your lot if possible. However, if that’s not possible, the vertical pipe may be the only method. Ground water isn’t “pressurized” per se, but the whole table level rises as it ‘floods’. The vertical pipe would work well to drain surface water to a lower water table level during drier times, but if the whole water level rises during the wet season, the only real solution is to duct the surface water off the property horizontally.

I don’t know the particulars of your lot in the neighborhood, so it’s hard to tell you exactly what to do. Do you have an alley, or some sort of access to a storm drain nearby?

Tripler
I’ve got another idea, which worked on my place in Jersey, if you do . . .

4

How good a job does your Moat do at keeping the Black Knight at bay? :smiley:

I’ll get my coat…

5

This is the fancy way of saying fill in the low spots. Make sure the house is higher than the rest of the yard.

6

Is it conceivable that the “moat” what created on purpose, precisely to drain water away from the fundations in case of heavy rain?

7

This is correct. However, knowing the house is currently built, it’d be a bit tough (and expensive) to raise the house off the foundation and backfill the bajeezus out of everything. It’s a distinct possibility the low spot developed after the house was built. . .

He could regrade the entire yard and lots surrounding his, but the easiest way would be to provide a controlled path for the standing water to escape.

Whether that’s a vertical or horizontal path depends on his neighborhood. clairobscur may be on to something, but it’s not usually desired to leave standing water on one’s property.

Tripler
Unless it’s a swimmin’ pool, evaporation bed, or a sewage lagoon, standing water is just a bad idea.

8

Since the property used to be a farm, it’s quite possible that ditch is there on purpose - built so the fields (which now comprise your yard) wouldn’t flood.

My guess is you have a very high water table, which is why the trench is there. Therefore, the suggestion you were given wouldn’t be too effective. Water is only going to run off if the ground becomes saturated, or if it is too dry to readily absorb the volume.

Unless the water remains long enough to become stagnant, which will cause an odor and an insect problem, I wouldn’t worry too much about it. Build a couple of decorative “bridges” across it, put a few large stones in it, and think of it as a babbling brook. Better than slogging through an inch of mud over your entire property for a week after each heavy rain.

Does the water flow? Have you followed the trench downstream? It may have an exit which is blocked by debris.

9

Raise the house? OG no, that would be way to much like work. :eek:
Regrade the yard, from the OP

If you filled in the low spot you would still hae an 18" drop between the house and the rear property line. Assuming the backyard is machine accessible this would only take a couple of hours with a tractor and a dumptruck or two full of dirt.
Of course without seeing the lot in question, it is pretty much impossible to give an exact recomondation of the best way to channel the runoff.

Not that it matters, but I had a similar situation in my backyard. Water would pool right at the end of my patio and at the corner of my detached garage. This was due to the traffic patern of walking out to the garage over the years. I extended the patio, and filled in the low spots, and now the water drains away from the walking area, and does not pool in my back yard.

10

Your best permanent solution might be to locate your natural “moat” swale to a less inconvenient location and a retention or detention area for the excess water . The pool table like topography in my area on the eastern shore of MD often requires these be constructed.

Retention vs Detention Pond

11

And to that end, in place of an often-troublesome culvert, you may consider installing a French drain. (If you live in a conservative state, you can refer to it as a “freedom” drain instead. :wink: )

As others have mentioned, the New England area generally has a fairly shallow and well-supplied water table; boring a hole down to the aquifer for draining may be ineffective and possibly even counterproductive. Building a detention pond, while expensive, is likely to be more effective, particuarly if the ground and table become saturated in heavy rain.

Stranger

12

I’m not an expert on this sort of thing, but I’m pretty sure that 18" over 250+ feet is not nearly enough to ensure proper drainage. If the OP fills in the ditch and flattens out the entire area, it won’t drain to the back of the property, but will rather be a mass of large shallow puddles for extended periods of time.

13

My reservations about the plan have to do with sending untreated water directly to the aquifer. Most of the water going into the aquifer will seep through many feet of porous stone, filtering nearly all the impurities. If you provide a direct chute to the water table from the yard, anything that gets into the yard (e.g., dog poop and occasional goose guano?) goes straight to the drinkning water.

Folks in my old neighborhood used to use something similar: they would dig a hole and sink a 55 gallon drum with neither a top nor a bottom into it, then fill it with coarse stone (3s and 4s to about a foot from the top, then a screen covered with gravel). Each drum removed quite a few gallons of water from the yard and got it down where it could start percolating downward without actually interfering with the aquifer. However, I do not know how practical that would be for an area as large as you describe.

14

aaaack!

1s and 2s to fill the barrel. (As I was composing, I was thinking they needed to use 1s and 2s and NOT 304 stone (pronounced three-oh-four), so, of course, I typed 3s and 4s.)

15

The minumum channel slope I use is 0.4%; or 0.004 ft/ft. Over 250 feet that’s 0.004 * 250 = 1 foot. So, the 18" of fall is sufficient to drain water away from the house.

Any of these ideas involving gravel drains would work to “wick” the water away, over a period of time. If standing water/soggy ground is your issue, then the contractor’s gravel “chimney” drain or tomndebb’s 55 gallon drum will work IF there is enough hydraulic gradient between the “moat” and wherever the outlet is; it might just take a long time to dry up. However as you already have a high water table, these drains probably won’t work at certain times of the year - there won’t be anywhere for the water to go.

If this were my place, I’d do as Cillasi suggested, and trace the outlet of the trench. I usually recommend a drainage system with as few structural elements as possible, to cut down on future maintenance costs.

The best solution IMO is improving the outlet of your existing swale so that the water drains off.

16

In addition to what Gorsnak said about that possibly not being enough of a slop, do check your deed restrictions/covenants/ordinances/etc. before you do anything like that. You could adversely affect the drainage of the neighor in back of you, which is often a legal no-no.

What the contractor is suggesting is called a dry well. Without knowing more about the geology in your area there’s no telling if it would work–you might want to look into consulting an engineer (or just giving your contractor a shot).

17

If the water table is rather high in your area, you could try the opposite, build a pond by digging deeper.

18

According to NinetyWt there is enough slope assuming the OP’s measurements are correct.
When you quoted me, you left out one very important sentence:

The op also might want to consider moving the low spot to a more useable location, such as closer to the rear property line, if drainage is not practical / legal.

19

I took NinetyWt’s comments to be referring to the slope needed in a drainage channel or ditch, not the slope needed on a flat field. But perhaps I misunderstood.

20

You need to know how big an area drains into your moat. Next time is rains hard, put on your boots and take a walk. If everything within 1/4 mile runs to you, your solution may have to be bigger than you had in mind.