We built a house on till derived soils - 3.5 feet of gravely sandy loam on top of impermeable hardpan. We set the foundation on the hardpan and leveled the soil around the house and so dug down to the hardpan uphill from the house. We built a swale and foundation drain to divert the seasonal ground water flow around the house and so I don't think we need to do anymore to control the ground water flow. However, there is a strip of land, about five by 40 feet, uphill from the house where the ground water percolates out of the ground for several days after each heavy rain. I expect it will remain saturated with water from October through April then dry out (unless I water it) in the summer.
We returned the topsoil to the graded areas around the house (acidic, low nutrient but 16% organic content) but that just turns to deep soft mud in this area and so I'm thinking that is the wrong soil type to use. I thought of following rain garden construction and planting techniques but those instructions say they are not for areas with high ground water. I'm also guessing it is too wet for a tall hugel (I don't want a mudslide into the house). We also don't really want to put some sort of pond in this area, plant trees this close to the house or pant grass that needs mowing.
Would it be possible to stabilize the soil (enough to walk on) by adding something like peat or pea gravel in this area and then maybe plant some sphagnum moss or ericaceous shrubs?
Uphill from the house you hit the seasonal water table, you can probably try to drain that water downhill of the house with some parallel swale and perpendicular drainage ditch to 'pond' lower down the slope. However the uphill land might become super dry in the summer growing season if you mess with the recharge cycle.
Overall it seems like whatever you are doing is recharging, a situation alot of people wish they could replicate on their parched plot of land.
The uphill neighbor has two acres of turf grass and a berm along our common property line and so all the rain that falls on his property ends up as ground water flowing through mine. Our property does dry out in the summer and I have ideas for tapping into the ground water such as underground hugels but I'm down to the hardpan in this area. I could put something like sand or gravel under the topsoil in the wet area and turn the swale into a French drain and so make the wet spot go away but just for landscape diversity I was trying to figure out something more creative for the wet spot like some sort of bog garden. I'm just concerned that the ground is like Jello now.
hau Sherwood, If you don't mind, please go to your control panel and select profile and add some information about your location so you can receive better help information on your particular situation.
It sounds like your land is a typical seasonal spring situation and there are particular things you can do that won't mess up natures design.
Once I can take a look at the geographical area and do some research on aquifer types and depths, soil make up over all and so forth, I'll be better able to give you some ideas on how to proceed.
I added an address to my profile. Western Washington state. Near the top of a ridge with southwest exposure and a 0% to 10% slope. Alderwood (Agc) soil with no outwash layer or aquifer above the 180 foot thick till layer. 122.06510°W 47.31283°N
Genevieve Higgs wrote:Is there opportunity to plant trees or other deep rooted things right up at the top above your seep? Im imagining slowing and spreading the water vertically through a lovely food hedge...
That might work farther uphill and help hang onto some of the water but I expect it would saturate and so not stop the ground water from reaching the seep during our long wet winters. We are trying to follow the Firewise guidelines and not plant trees as close to the house as the seep is. Also there is only the few inches of topsoil we put back because I have to maintain the slope away from the house and so there's not enough for deep rooted things.
It would seem that your soil is based on decomposed granite, this means the soil will be slightly acidic and drain well.
Since you say you have hardpan subsoil under differing clays, this would mean you are in a drift area of previous volcanic activity, gray clay is this area should be basalt ash deposits and red clay would indicate a deeper in the volcano sediment with iron as the main mineral.
The water seepage is indeed a seasonal spring situation, the best choices would be either a pond at the top with swale/berm construction leading away from the pond and out towards the nearest ridge line at a 1 degree slope.
Swales would work best if wide and shallow with a dead level top edge of the berm, to sheet extra water down the hill without eroding soil in gullies.
You also have the option of making the swales but putting a pond at the bottom (this would require a pump to move water back up hill as needed, not exactly the best choice perhaps, just depends on your needs).
I'm still researching the cascade mountains and other parts of the Sierra Nevada Range in Washington State, I'll give more possibilities as I can get the information.
There is some volcanic ash content to the soils but it is mostly PH 4.8 sandy loam. Weyerhaeuser logged this land several times and there seems to be a lot of organic matter (16%) that somehow got mixed into the top foot or so but has not broken down to humus yet. There is not much alive in the soil and I have only seen one earthworm after a lot of digging. It does drain well down to the till layer. I think our current swale is working well enough (basically chiseled into the hardpan) and so I'm just trying to decide what to do with the wet spot on the uphill side of the swale. I have seen rain garden instructions that say to add a lot of compost and a bog garden instruction that say to add a lot of peat. Since it is already very acid and high organic content I'm not sure those are the right things to do.
Instead of peat you might want to try lots of wood chips.
The high acidity does indicate that your soil came from granites (not unusual since you are in the Sierra Nevada Mountain Range and it is a volcanic mountain range).
The soils all through that mountain range are rich from ancient volcanic ash and rotted granites which make up that sandy loam.
In the High Sierras if you find clay, you can be sure that it is volcanic in makeup. This is also an area that has fairly deep forest litter and fire is the natural disruption factor.
If you wanted to raise the pH fairly quickly you would have to use amendments.
The reason there are no earthworms is the acidity.
Compost extracts and ground up sheet rock are good, inexpensive ways to start raising that pH to ranges that microorganisms can tolerate.
Right now there are just a few fungi that can survive in those soil conditions and those are the mycorrhizae fungi (arbuscular for the most part).
One of the things you don't have to worry about much is trace minerals.
It sounds like you have a fairly good plan for water control.
I'd locate some local plant material that lives in the conditions you have (a few hikes might help you find ones you like and want to have)
I used to hike the California Sierra range and it was not uncommon to find fields of pitcher plants and rushes in the type of conditions you have.
That's a good idea for plant selection. Most of the seeps and springs in the area are in valleys that cut through the deeper aquifers and have a much higher PH. However, the seasonal wetland just off the low SW corner of my property must be wetted by the same ground water flowing through my property. I'll muck around there next spring and see what I find. I seem to remember a lot of wild ginger but maybe that wasn't right down in the wettest part.
Wood chips are another idea. Maybe I'll divide my wet spot into two or three sections and try different materials to firm up the soil and see which the plants seem to like.