New Drainage /Sump Pump

Discussion in 'Pumps and Tanks Well Forum & Blog' started by BARRETT, Apr 21, 2006.

  1. BARRETT

    BARRETT New Member

    Messages:
    2
    Greetings,

    Looks like a great site, just found it. I am planning to install a sump pump to enhance poor drainage between my neighbor's house and mine. We are on the same page and have selected where we want to locate the sump, tie in some downspouts and also create and tie in a 20 ft. long french drain in a low spot. I was planning on using a plastic culvert pipe for the sump structure - 14" minimum diameter per pump spec's. I have both perforated and solid flex line already. Planning on using solid for picking up the downspouts and perforated for the french drain - sound OK?

    I have purchased pvc pipe, a 3/4 hp sump pump and the electrical supplies needed to power it. Still need to get a check valve, HD was out so I'll get that today elsewhere. My questions are: what other supplies will I need? What is the gradient required for the flex lines and french drain lines feeding into the sump - 1/4" per foot, more? How do you 'seal' the drain lines penetrating through the sump walls - is it even necessary? Should I place drain rock in the bottom or use bricks and the like to keep the pump out of the mud, both? I need to wrap the perforated french drain flex line, any particular brand/type recommended?

    Thanks,
    Barrett
    No. Cal
  2. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    I don't have the details but here is an example of factors you might want to consider.

    Let's say that you have 6400 sq ft of roof and pavement draining into that sump, and in a bad rainstorm that you want to design for, you have 1.5" per hour. So you have 800 cubic feet of water per hour. That is 6000 gallons per hour, or 100 gallons per minute. You do the numbers, based on your drainage areas, and recent rains in northern California or on the rainfall chart at the site below.
    http://www.mifab.com/pdf/r-sizing-us.pdf

    Then you figure out how much lift you are going to need with that pump, and how big a discharge pipe you will need. How much elevation difference + pressure losses + margin of safety for pressure loss. Maybe use 15 ft of head at 100 GPM. So in that case you would want a pump that handles 100 GPM at 15 ft of head, plus whatever flow and head margin makes you comfortable.

    At 100 GPM a 2" discharge pipe is probably a little small for a low-head sump pump. Figure 3" or use some of your 4" pipe.

    You are running direct rainfall runoff into this sump. Is there any chance that it will flow back into your house when the electricity fails? Water might run the wrong way if the sump overflows.

    You are going to need some kind of pressure connection to that pump. Not much pressure but it won't be a gravity drain. And you need some place to put the water where it won't cause erosion. Maybe some nice rocks for a runout.
  3. prashster

    prashster New Member

    Messages:
    941
    (not a pro)
    I had a similar issue. The advice I got from the twp engineer is that the grading should first be addressed. If you have a low spot, is there a way to fix it economically that way?

    If that's not an option, I'd try a French drain all the way from the low spot to the street or wherever you're draining to. This may require significant depth/width of the trench, but it's better than an electric option.

    If you can't do either, then for the sump, you want to keep it open to water, but closed to debris. Dig the pit wider and deeper than necessary and backfill with coarse gravel to promote better drainage.

    But for my money, I'd chose one of the 1st 2 options.
    Last edited: Apr 21, 2006
  4. speedbump

    speedbump Previous member

    Messages:
    4,540
    Location:
    Riverview, Fl.
    Something else to consider:

    If you put a 3/4hp sump pump (I assume you bought a sump pump, not a sewage or effluent pump) and it pumps say 30 gallons per minute and you put it in a 14" enclosure, it's raining fairly hard but not hard enough to keep this tiny little pit full, your pump is going to be hammering off and on until it dies. Your sump pit should be on the order of at least 200 or more gallon capacity so the pump can run for a while then be off for a while.

    I sell Myers Sump, Effluent and Sewage pumps. The Water Ace version (made by Myers) in the big box stores are 1 hp increment higher than my Myers. In other works their 1/2 hp Effluent pump would be my 1/3 hp effluent pump and so on. I always say, buyer beware.

    bob...
  5. BARRETT

    BARRETT New Member

    Messages:
    2
    Gents,

    Thanks for the responses. To clarify - I have an open drainage ditch in front of the house. The bottom of the ditch is roughly level with the bottom of my driveway just in front of the garage. So, gravity draining of the area is not an option. Our homes are slightly downhill from the street, not a huge grade or distance but enough to make this a small project. There is an existing 2" pvc pipe which I am going to connect to. It is left over from a previous attempt to enhance drainage, unfortunately one of the previous owners put their fenceposts right through the old outflow line!! I checked to make sure the existing line is not blocked under the driveway entry. I have removed an old concrete area drain box which was connected to the 2" pvc and plan on putting my new sump in a nearby location. There is no sign of a prior pump installation, so I think this was little fake-out for the inspector - there were requirements for french drains and area drains on my street many years ago. I have also found an old "french drain" running along the opposite side of the house - it was about a foot wide and had about 6" of drain rock but no pipe underneath it. So, who knows what all this junk was meant to be but it doesn't drain.

    To answer a few of your questions: No, failure of the sump pump/elec won't hurt anything since the sump is between the two houses. I am planning on placing the pump about 4 feet below grade. The remaining head is only about 1 - 1 1/2 feet. I chose 1 1/2" pvc pipe since that is the size of the pump's discharge. The 2" pvc I am connecting to is plumbed through the driveway culvert pipe. The two homes share a long (40 feet) driveway entrance with a culvert pipe running underneath and asphalt covering the top third of each driveway, the remainder down to the garage is concrete. My pump lists max. capacity at about 7,000 gph. With a 5 foot head, I think it will deliver 4-5,000 gph. I will be picking up 2 downspouts and so will the neighbor. That is about 1/2 of each roof, probably less given the way my roof is constructed. I will do some math via the link given for computing run-off from the roofs.

    To be continued.... thanks,

    Barrett
    Last edited: Apr 21, 2006
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