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I’ve built quite a few french drains in residential settings, some lasting longer than others - I’ll share a few hard earned lessons here: Soil migration is th

• daedrdev 2y ago
  The video also mentions that sometimes the geo textile fabric is not enough since it too can get clogged, though this seems important in dams and not so in simpler projects
  • bshacklett 2y ago
    If you live in a place with a lot of clay, geotextile fabric can certainly be problematic for simple residential settings.
  • datavirtue 2y ago
    The drain pipe is at the bottom of the drainage excavation. On top of the pipe is 3/4 aggragate, and on top of the aggregate is geotextile. Soil is filled in over the geotextile. There is no clogging risk in this design. Any soil particles that make their way to the pipe are carried away.
    • cityofdelusion 2y ago
      Fine clay and silt clogs the geotextile. A proper drain requires extensive soil testing for particle size. Video goes over this along with the issues of geotextiles.
      • datavirtue 2y ago
        Yeah, I saw that video and many others long before it was posted here. I stand by my comment, which is based on experience and reviewing the work of professional drainage installers on YouTube. No one is doing soil tests for these unless they are installing huge critical commercial infrastructure.
• ejstronge 2y ago
  >Calculate how much water you actually need to drain. You can use the “100 year flood” values for your locale to get an upper bound on rainfall, then multiple by drainage area How do you incorporate this into a drain design?
  • toomuchtodo 2y ago
    https://web.archive.org/web/20240807170330/https://www.ndspro.com/PDFs/Tech-Spec-Guides/definitive-drainage-guide.pdf https://web.archive.org/web/20240807170330/https://www.ndspr... https://web.archive.org/web/20240807170407/https://urban-water.co.uk/french-drain-design-guide/ https://web.archive.org/web/20240807170407/https://urban-wat...
    • ejstronge 2y ago
      Both of these links include a dry well - if one is draining to daylight, how do you incorporate the 100-yr flow rate?
      • toomuchtodo 2y ago
        Can you share what daylight looks like for your use case? Where is your target for the water to be managed?
        • ejstronge 2y ago
          Daylight means a field whose elevation is below the area to be drained in this case
• hatsix 2y ago
  Not sure you watched the whole video, he shows how soil migration causes failure (7:30), links to another video that covers that in-depth and discusses how geotextile isn't enough for things like damns (10:15). He also mentions that you can get pipe with holes all the way around (5:58).
  • ryanisnan 2y ago
    Definitely didn't watch the video. He also mentions hole direction and problems, as if the video didn't go at length into the topic.
    • refibrillator 2y ago
      I definitely watched it but missed a couple of those sentences so thanks for the timestamps above. Yes he does name soil migration as the biggest problem with subsurface drains, but to be fair the video is contextualized around dams. The spirit of my comment was intended to be helpful for folks attempting this stuff at home, not to suggest a lack of good info in the video.
      • ryanisnan 2y ago
        Ah, ok, no worries. Apologies, I should have given you the benefit of the doubt. Your comment was generally insightful.
• xg15 2y ago
  > You can use the “100 year flood” values for your locale to get an upper bound on rainfall I wonder, does climate change also affect those calculations, with the need to adjust those bounds upwards? I remember the (technical) term "100 year flood" getting lots of ridicule in the last years because we already got multiple "100 year floods" in the range of a decade.
  • jnwatson 2y ago
    Faster than climate change is development. The addition of impermeable surfaces like parking lots and buildings upstream causes more water to get to you. Development happens faster than the flood maps get redrawn.
    • susiecambria 2y ago
      I wonder how well USA state agencies are doing in their efforts to map sea level rise, flooding, etc. and if they take into account development. I know a lot of work is being done in Virginia to address sea level rise, flooding in poor areas, etc. But because I live in a rural part of the state, I can't assess for development since it's not ubiquitous.
  • dv_dt 2y ago
    Short answer yes, but as another comment suggested, development changes adding hard surfaces in new places in the neighborhood also rapidly change those calcs.
  • magicalhippo 2y ago
    If it was me I'd chop a zero off those N-year estimates. But that got me thinking, how often do they adjust these estimates? Was a "100 year flood" in 1950 less than in 2000, say? Obviously it'll be different for different areas, especially between countries, but still.
  • mindslight 2y ago
    FWIW "100 year flood" refers to the flooding that is expected to occur in that specific area on average once every hundred years, not an event that will happen only once over the whole country once per hundred years. So regardless of climate change it makes a lot of sense to be seeing many hundred year floods since mass media has us caring about many areas in parallel, not just the specific area we live.
• datavirtue 2y ago
  The roof should be shedding to solid drain pipe.
  • orthecreedence 2y ago
    Yes, "should." I've found that should happen and did happen are two very different things when it comes to a lot of homes. Incidentally, our roof had gutters/drainage originally. We put in our own french drain after about 8000 hours of research, and decided to re-route the roof drainage to right above the new french drain (separate pipes) because the roof drainage broke at some unknown point and was dumping water around our foundation piers (yay...). Well, our roofers came and installed gutter guards after all this, which caused the gutters to shed 60% of the water into the drainage area because of the way they're angled. If we hadn't put in a french drain, it'd be a real problem, but as it is now, it's a mild annoyance that I keep telling myself I'll fix.
    • strunz 2y ago
      You should make them remove the gutter guards. If you're losing by that much water to your foundation, the gutters are kind of pointless now.
    • datavirtue 2y ago
      I have used French drains on buildings where I didn't want to install and maintain gutters. The roof shed straight into a gravel path (no soil coverage) around the building that had perforated pipe leading to a dry well. Worked perfectly. In one case the pipe had to be very shallow so I used crusher-run (404) aggregate to form better support around the pipe at the surface. Again, worked perfectly. You really have to watch the details and plan things out meticulously for the given situation.
• eitally 2y ago
  Our first house was one a 1/2ac lot at the end (bottom -- this will become important later) of a cul-de-sac in a great semi-urban neighborhood in Cary, NC. We learned after repeated backyard flooding and near-incursion of storm water into our patio door that our street had been built on what had been the original stormwater collection pond for the larger neighborhood. The builder got permission from the city to move the pond to build our cul-de-sac, but that didn't stop our street from still being the lowest point in the neighborhood, where all surface water ran-off to, and our house was at the very lowest point. Long story short, we ended up installing a french drain on two sides of our house, putting a drain at the end of our driveway to redirect water [from just running down our driveway to our house], having the front wall foundation rebuilt and jacked up because the footer had nearly completely eroded (1970s house), and still needed to add two 24" square drain boxes in the back yard (with buried 4" PVC draining into the creek at the back of the property) to remediate all this. It was also a tree-filled lot and the drain boxes would almost immediately clog with leaves during heavy rains, so I spent a lot of time out there in ankle to knee deep water with a rake to keep the drains clear. This still wasn't enough! We got a so much surface run-off from our uphill neighbors that it looked like a sheet of rushing water across our backyard during heavy storms. We had a creek at the back of the property but were not allowed to mess with it because of Corps of Engineers easement regulations. At the end of the day, we finally solved our problems by getting an agreement from our neighbor to let us dig a surface water drain from the low point in their yard into the creek, and then we'd build a "temporary" (cf prior easement rules against permanent walls) berm along the property line to prevent surface water from coming into our yard at all. That "berm" was 76 bags of Qwikrete stacked three high and covered with grass clippings, yard waste & mulch. Technically we could have removed it if the city had inspected, but it was very much a cement wall. We have never since, and never will, build or purchase a house at the bottom of a hill.
  • kbenson 2y ago
    One of the prior houses I lived at had so much flooding and water leakage problems from poor construction (prior additions that weren't strictly legal) that lead to carpet and padding having to be removed from concrete floored rooms and eventually mold problems, that when I bought a house a few years after we'd ran away from that disaster of a house we made absolutely sure to my at the high point of the (new) neighborhood so we weren't in the drainage path for anyone. It's particularly demoralizing to see the scope of the problem when it's all that water flooding your property and know there's nothing you can do in the short term, and even the long term is just trying different things and hoping they work, knowing that it will probably take a few tries.
• ajb 2y ago
  Depending on how deep it is a drywell can be an EPA regulated thing in the US. This is because it can be a bad idea to sink surface water directly into the aquifer - naturally it would be filtered by the overlying soils, if it goes in directly then any surface contamination is washed directly into a reserve of drinking water. But, I'm far from an expert so I can't give any advice as to when one would need registration etc.
• jiveturkey 2y ago
  Are you in the construction or related business? I've had to learn some of these things the hard way myself. I learned I was outclassed and so I hired a geotechnical engineer to design my now-deployed drainage. (french drain plus site drainage) I wonder what building codes require, ie from engineering and inspection POV, like can the things you mention even be built today? If so isn't this a failure of the planning departments?
  • pests 2y ago
    > like can the things you mention even be built today? Yes definitely, just depends on area and your local geology / codes.
• amluto 2y ago
  > To prevent soil migration you absolutely need commercial grade geotextile fabric wrapping the gravel and pipe. The article seems to be quite clear that, for critical applications, one should not use geotextile fabric at all — instead one should use (appropriately selected!) sand.
• nogridbag 2y ago
  Any advice for homeowners living in a high water table area besides "move"? We were a bit naive buying our new construction home. It's the only home on the street with a basement due to the high water table. One year after purchasing, Hurricane Ida hit and we had water up to the door handles in our basement. Our primary sump pump runs constantly for 18 minutes then off for 18 minutes 24/7. We have a backup pump on the other side of the basement connected via the perimeter drain, and a liberty water backup pump. The only addition since Ida is a whole house generator and superior window wells. During Ida, the street was flooded, the drainage systems were backed up, and there was no where to pump the water to.
  • ethbr1 2y ago
    Unfortunately, you can't "drain" into saturated soil. At that point you're building a boat more than a house: keeping water out on all sides. I'm assuming it's a fully-enclosed basement? I.e. no walk-out side? The best you can likely do is waterproofing the basement walls + pumping out from inside or an inside-perimeter drain. But that's only racing pump_out_flow > seep_in_flow. And that's a bad game to be in, because water under pressure (which it will be a story below ground) finds a way. I'd make the basement flood tolerant (limit mold-hosting materials and places water can be trapped) + pump it out quickly after it floods + buy a dehumidifier, and accept it's going to happen.
    • hedgehog 2y ago
      As far as I can tell inside waterproofing is a bad idea, it leaves your foundation soaking wet, excess humidity indoors, and as you point out it doesn't alleviate the pressure from outside. Waterproofing the exterior, french drains deeper than the footings (all sides), and sump pumps... That should keep things dry but it's quite a process.
      • ethbr1 2y ago
        Foundations being wet aren't a huge deal. Exterior is recommended over interior because it's easier to ensure no gaps. But it does involve substantial excavation. French drains around the perimeter help, but you're literally fighting water from all directions... including directly underneath. Have a perimeter French drain but a crack in the slab? Enjoy watching water bubble up from that crack once things get saturated.