Calculation on French Drain

Discussion in 'Landscape Architecture and Design' started by coxlandscaping, Jan 12, 2007.

  1. coxlandscaping

    coxlandscaping LawnSite Member
    Messages: 104

    I need some advance on a French Drain I need to know how to calculate how much containment in the ditch and size pipe to hold about 1.32 Acres Roughly getting about 2” of rain with percentage loss through rock before reaching the French Drain we build there containment ponds but this is the first time they have wanted us to do there drainage. This is an addition to a water treatment plant for the city they use Sturlin (not sure of spelling) on there fences around the station which has to be contained
  2. tthomass

    tthomass LawnSite Gold Member
    from N. VA
    Messages: 3,498

  3. AGLA

    AGLA LawnSite Bronze Member
    Messages: 1,778

    You have to know the perc rate of the soil that you are draining into, the "C" value of the area that is draining into it, the time of concentration, .... It is a job for an engineer to calculate and a separate job for you to build it to those spec's.

    You have about 10,000 cubic feet of water landing on that site (.1666' x 43,560sf/acre x 1.32 acres = 9,579 CF). That's only 71,650 gallons in a 2" rain fall. If it is a paved and roofed site, almost all of it has to be dealt with. If it is a forest, only about 20% of it has to be dealt with.

    You really need someone with the training and credentials to calculate the area of different surfaces in order to know how much water you need to deal with. After that, he has to determine how to deal with it - detention pond, or catch basins and leach pits, grassed swales, ... or some kind of combination. Then the perc rate of the soil is going to determine how fast it is absorbed into the ground which will determine how much standing water you have to contain. It is a pretty exact science in some respects, but there are lots of variables. Some of those variables are physical and some of those can be chosen as part of the design. One thing is for sure. That is that no one is going to be able to give you a correct answer over the internet.

    This is not responsibility that should be put on a landscape contractor. It is definitely not one a landscape contractor should assume.
  4. coxlandscaping

    coxlandscaping LawnSite Member
    Messages: 104

    I don’t understand why this would not be laid out on there Site Plans we started laying out for the Containment Pond today everything on the drawing but all that I saw on the drawing was showing drains coming into the containment area but no details on drawing etc. I will go to there office on Monday to see if there are any drawings that may not have made it to the site office if not I don’t know really what to tell them other than they will need to get us something on it
  5. start2finish

    start2finish LawnSite Senior Member
    Messages: 497

    your customer either doesn't know that he needs an engineer or is trying to cut a corner.

    not to hijack this thread, but ALGA this is a good representation of the landscape design area and charging for it, it is simple to explain and need an engineer to do this and will not be questioned that he needs to be well compensated for this work, now people want knowledge of plants and soils for landsscape design for free. because our industry lets it be so.
  6. AGLA

    AGLA LawnSite Bronze Member
    Messages: 1,778

    The difference is that they see 200 landscape contractors in the yellow pages and 500 more driving around, but they only see five engineers in there. Then they assume that each is the same, so whatever one knows the rest know as well. They then think that everything done by a landscaper is common knowledge because there are so many of them. If it is common knowledge, it can't be worth much.

    You know and I know that there are highly intelligent and highly experienced, if not highly educated, landscapers out there amongst the crowd that also includes knuckle dragging mouth breathers. It is pretty difficult to take such a diverse field, landscaping, and create a perception that there is a high standard of knowledge, ethics, and ability when the reality is that it is very obvious to the public that there are people in it that don't walk that walk.

    In a way this is a good thing because you can easily be recognized as being better than average without too much difficulty. It would be easier to be perceived as average if everyone thought landscapers were ALL brain surgeons.

    Promote yourself within the industry rather than promoting the industry as a whole and hoping to stay on for the ride. When more people raise the bar, the industry moves upward, but the bottom feeders will still be on the bottom.
  7. coxlandscaping

    coxlandscaping LawnSite Member
    Messages: 104

    That’s true we have been in this business for a long time me personally for about 23 years my uncle whom is the owner a heck of a long time and as a part owner I rely on him a lot for his advice and knowledge. With that said it’s amazing how many people that we have seen come and go they come into this business like there going to conquer the world in one summer some will lie and would cut your throat to take your work. I have had both customer and contractor come to us about so and so and do the job for x amount cheaper one thing we will not do is compromise on the quality of the work we do we will work with our contractors if we can and yes we have lost some work but most of the time they come back. With this said because we have been around along time that it’s taken for granted that we know everything about it and let me just say we are still learning new things and you will always learn if you don’t you will be out of business or as you say a bottom feeder

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