{"id":606,"date":"2015-01-13T17:09:40","date_gmt":"2015-01-13T17:09:40","guid":{"rendered":"http:\/\/www.tempoinc.com\/?page_id=606"},"modified":"2015-02-16T23:51:41","modified_gmt":"2015-02-16T23:51:41","slug":"drainage-design-guide","status":"publish","type":"page","link":"http:\/\/www.tempoinc.com\/dev\/drainage-design-guide\/","title":{"rendered":"Drainage Design Guide"},"content":{"rendered":"
<\/p>\n

\"10<\/p>\n

Download Tempo Drainage Design Guide<\/a><\/p>\n

Basic drainage design is relatively simple by following this easy 10-step process.<\/h2>\n

 <\/p>\n

Before we start there are 4 important points to remember:<\/h3>\n
    \n
  1. Excess water always collects at the lowest elevation points.<\/li>\n
  2. Design for worst case conditions and not for average conditions.<\/li>\n
  3. Although obvious, water can only flow downhill.<\/li>\n
  4. Be generous in the design-if in doubt add an extra collection point (grate) and rather oversize than undersize a component.<\/li>\n<\/ol>\n

    In order to help understand the basic steps of designing a drainage system, consider the following example:<\/h3>\n

    A contractor needs to install a drainage system in the backyard of a house in Atlanta, Georgia. The backyard is comprised of 3 areas, a loamy soil flower bed, a grass area and a concrete deck. The flower bed area is 6\u2019 wide x 20\u2019 long (area of 120 sq ft), the grass area is 20\u2019 wide x 24\u2019 long (area of 480 sq ft) and the concrete deck area is 40\u2019 wide x 20\u2019 long (area of 800 sq ft). The distance from the backyard to the street is 100′.<\/strong><\/p>\n

    STEP 1:
    \nDetermine the Rainfall Intensity of the property.<\/h2>\n

    Different parts of the country have varying rainfall intensity profiles. Use Table 1.1 below to determine the Rainfall Intensity (I) of the property. Keep in mind that the table below has been simplified (more sophisticated data is available on the web that contain 100 year one-hour rainfall maps, etc.)<\/p>\n

    Table 1.1<\/strong><\/p>\n\n\n\n\n\n\n
    Rainfall Intensity Zone<\/td>\nStates in the USA<\/td>\nRainfall Intensity<\/td>\n<\/tr>\n
    Zone A<\/strong><\/td>\nAL, FL, GA, HI, LA, MS, NC, OK, SC, TN, TX<\/td>\n5.0 inches per hour<\/td>\n<\/tr>\n
    Zone B<\/strong><\/td>\nAR, CT, DE, DC, IA, IL, IN, KS, KY, MA, MD, MI, MN,MO, ND, NE, NH, NJ, NY, OH, PA, RI, SD, VA, WV, WI<\/td>\n3.5 inches per hour<\/td>\n<\/tr>\n
    Zone C<\/strong><\/td>\nAK, AZ, CA, CO, ID, ME, MT, NV, NM, OR, UT, VT, WA, WY<\/td>\n2.0 inches per hour<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

    As the property in our example is in Atlanta, GA, it falls into Rainfall Intensity Zone A with a Rainfall Intensity of 5.0 inches per hour.<\/p>\n

    STEP 2:
    \nCalculate the maximum run-off potential flow for each area.<\/h2>\n

    In order to correctly size the drainage pipe network, the maximum run-off flow for each area must be calculated. A frequently used formula for calculating the maximum runoff potential from a small area (under 200 acres) is the Rational Method. The Rational Method Formula is:
    \n\"rational-method-formula\"where:
    \nQ = peak runoff flow (gallons per minute)
    \nC = coefficient of runoff
    \nI = rainfall intensity (inches per hour)
    \nA = drainage area (square feet)<\/p>\n

    For our example, we already know the area (A) of each zone to be drained. The flowerbed is 120 sq feet, the grass area is 480 sq feet and the concrete deck area is 800 sq feet.<\/p>\n

    Next, we will determine the coefficient of runoff (C) for the surface type of each area to be drained using Table 2.1 below. The coefficient of runoff for the loamy soil flowerbed is 0.45, for the grass area is 0.35 and for the concrete deck area is 0.90.<\/p>\n

    Table 2.1<\/strong><\/p>\n\n\n\n\n\n\n\n\n\n
    Surface Type<\/td>\nCoefficient of Runoff<\/td>\n<\/tr>\n
    Concrete or Asphalt<\/strong><\/td>\n0.90<\/td>\n<\/tr>\n
    Clay<\/strong><\/td>\n0.60<\/td>\n<\/tr>\n
    Gravel<\/strong><\/td>\n0.50<\/td>\n<\/tr>\n
    Loam<\/strong><\/td>\n0.45<\/td>\n<\/tr>\n
    Sand<\/strong><\/td>\n0.40<\/td>\n<\/tr>\n
    Grass<\/strong><\/td>\n0.35<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

    Lastly, we will use the Rational Formula to calculate the peak runoff flows for each area.<\/p>\n

    For the flowerbed: Q = (0.45 x 5.0 x 120) \/ 96 = 2.8 gallons per minute
    \nFor the grass: Q = (0.35 x 5.0 x 480) \/ 96 = 8.8 gallons per minute
    \nFor the concrete deck: Q = (0.90 x 5.0 x 800) \/ 96 = 37.5 gallons per minute<\/p>\n

    Adding these together, the total combined area maximum runoff flow (Q) is 49.1 gallons per minute.<\/p>\n

     <\/p>\n

    STEP 3:
    \nChoose the number of drainage zones.<\/h2>\n

    When designing a drainage system, attention must be paid not to exceed the maximum flow capacities of the drainage pipe (as show in Table 3.1 below). Using either 3″, 4″ or 6″ drainage pipe is recommended on most residential and light commercial projects as these pipe sizes and applicable fittings are readily available and easy to install.<\/p>\n

    Table 3.1<\/strong><\/p>\n\n\n\n\n\n\n
    Pipe Size<\/td>\nMaximum Flow Capacity<\/td>\n<\/tr>\n
    3″<\/strong><\/td>\n44.0 GPM<\/td>\n<\/tr>\n
    4″<\/strong><\/td>\n75.0 GPM<\/td>\n<\/tr>\n
    6″<\/strong><\/td>\n175.0 GPM<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

    In our example and using Table 3.1 above, there are two choices to accommodate the maximum property run-off flow calculated in step 2 of 49.1 GPM.<\/p>\n

      \n
    1. A single 4″ or larger pipe may be used (a single Drainage Zone system).<\/li>\n
    2. Two separate 3″ or larger pipes with two discharge points could be used (a two Zone Drainage system).<\/li>\n<\/ol>\n

      For the example we are using, as 3\u201d pipe is easier to install and cheaper than 4\u201d or 6\u201d pipe, we will select a two Drainage Zone system using 3\u201d pipe with two independent discharge points. However, if 4\u201d or 6\u201d pipe is more readily available than 3\u201d pipe, you may choose to use that instead.<\/p>\n

      Drainage Zone 1 will comprise the flowerbed area and the grass area (maximum run-off flow for that combined area is 11.6 GPM) and Drainage Zone 2 (maximum run-off flow is 37.5 GPM) will comprise the concrete deck area.<\/p>\n

       <\/p>\n

      STEP 4:
      \nLocate the basin and\/or grate positions.<\/h2>\n

      Locate the low spots on the property where excess water could accumulate. Once these are finalized, they become the basin and\/or grate locations. In the example above, let us assume that each of the 3 areas described has a single low point within its confines. The first basin and\/or grate is located in the flowerbed, the second basin and\/or grate is in the grass area and the third basin and\/or grate is in the concrete deck. If there is more than one low point within an area, each of these would be a collection point and a location for a basin and\/or grate.<\/p>\n

       <\/p>\n

      STEP 5:
      \nDecide whether a flat or atrium (domed) grate is appropriate.<\/h2>\n

      Flat grates are typically used in areas where there is pedestrian, wheelchair, or light duty auto traffic. Atrium grates are domed and typically used where there is no pedestrian traffic and where mulching, leaves, or other debris could be present that could plug the flat grate.<\/p>\n

      In the previous example problem, assume that the flowerbed has been mulched and leaves may also be present. Therefore an atrium grate (Grate 1) is recommended. For the grass area, a flat grate (Grate 2) must be used as there will be lawnmower and foot traffic present. For the concrete deck area, a flat grate (Grate 3) must also be used.<\/p>\n

      STEP 6:
      \nSelect the appropriate grate size for each area.<\/h2>\n

      Using the maximum runoff flows from each area that we calculated in Step 2, divide each area\u2019s flow by the number of grates locations in that area to calculate how much flow each grate needs to handle. Once you have calculated each grate\u2019s flow requirements, use Table 6.1 below to select the grates.<\/p>\n

      Table 6.1<\/strong><\/p>\n\n\n\n
      \n\n\n\n\n\n\n\n\n\n\n
      Grate<\/td>\nMaximum Flow Capacity<\/td>\n<\/tr>\n
      3″ Round Flat<\/strong><\/td>\n3 GPM<\/td>\n<\/tr>\n
      4″ Round Flat<\/strong><\/td>\n6 GPM<\/td>\n<\/tr>\n
      6″ Round Flat<\/strong><\/td>\n16 GPM<\/td>\n<\/tr>\n
      6″ Square Universal<\/strong><\/td>\n11 GPM<\/td>\n<\/tr>\n
      9″ Square Flat<\/strong><\/td>\n50 GPM<\/td>\n<\/tr>\n
      12″ Square Flat<\/strong><\/td>\n70 GPM<\/td>\n<\/tr>\n
      18″ Square Flat<\/strong><\/td>\n120 GPM<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/td>\n\n\n\n\n\n\n\n\n\n
      Grate<\/td>\nMaximum Flow Capacity<\/td>\n<\/tr>\n
      3″ Atrium<\/strong><\/td>\n12 GPM<\/td>\n<\/tr>\n
      4″ Atrium<\/strong><\/td>\n20 GPM<\/td>\n<\/tr>\n
      6″ Atrium<\/strong><\/td>\n36 GPM<\/td>\n<\/tr>\n
      9″ Atrium<\/strong><\/td>\n40 GPM<\/td>\n<\/tr>\n
      12″ Atrium<\/strong><\/td>\n65 GPM<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/td>\n\n\n\n\n\n\n
      Grate<\/td>\nMaximum Flow Capacity<\/td>\n<\/tr>\n
      3″ Brass<\/strong><\/td>\n4 GPM<\/td>\n<\/tr>\n
      4″ Brass<\/strong><\/td>\n7 GPM<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

      <\/div>\n

      <\/p>\n

      In the example, for the flowerbed area (with only one grate location) and a maximum runoff flow of 2.8 GPM, we choose a 3\u201d atrium grate, which has a maximum flow rate of 12 GPM. For the grass area (with only one grate location) and a maximum runoff flow of 8.8 GPM, we choose a 6\u201d round flat grate which has a maximum flow rate of 16 GPM. For the concrete deck area (with only one grate location) and a maximum runoff flow of 37.5 GPM, we choose a 9\u201d flat grate which has a maximum flow rate of 50 GPM.<\/p>\n

      As we previously decided to use all 3\u201d drainage piping, check on Table 6.2 below that all of the grate sizes chosen can be used with 3\u201d pipe.<\/p>\n

      Table 6.2<\/strong><\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n
      Grate Size<\/td>\nPipe Diameter Options<\/td>\n<\/tr>\n
      3″<\/td>\n3″ pipe connecting directly on to grate<\/td>\n<\/tr>\n
      3″ Brass<\/td>\n2″ Schedule 40 or 3″ pipe1<\/sup><\/strong><\/td>\n<\/tr>\n
      4″<\/td>\n4″ pipe connecting directly on to grate<\/td>\n<\/tr>\n
      4″ Brass<\/td>\n3″ or 4″ pipe2<\/sup><\/strong><\/td>\n<\/tr>\n
      6″<\/td>\n6\u201d pipe and 3\u201d or 4\u201d pipe when used with 6\u201d catch basin<\/td>\n<\/tr>\n
      6″ Universal<\/td>\n3\u201d or 4\u201d pipe when used with or without 6\u201d catch basin<\/td>\n<\/tr>\n
      9″<\/td>\n3\u201d, 4\u201d or 6\u201d pipe when used with 9\u201d catch basin<\/td>\n<\/tr>\n
      12″<\/td>\n3\u201d, 4\u201d or 6\u201d pipe when used with 12\u201d catch basin<\/td>\n<\/tr>\n
      18″<\/td>\n3\u201d, 4\u201d or 6\u201d pipe when used with 18\u201d catch basin<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
        \n
      1. Fits 2\u201d Schedule 40 pipe attaching directly to PVC collar or fits 3\u201d pipe via 3\u201d S&D fitting.<\/li>\n
      2. Fits 3\u201d pipe attaching directly to PVC collar or fits 4\u201d pipe via 4\u201d S&D fitting.<\/li>\n<\/ol>\n

        There are no catch basins available for 3\u201d or 4\u201d grates as they connect directly to drainage pipe. When using the 9\u201d, 12\u201d and 18\u201d grates a catch basin or low profile basin must be used. The only time a decision needs to be made is when using a 6\u201d round or 6\u201d square grate. In our example, a catch basin must be used for the 6\u201d grate because we are connecting it to a 3\u201d pipe.<\/p>\n

        In our example, all three can indeed be used with 3\u201d pipe. The 3\u201d grate will connect directly to 3\u201d pipe, the 6\u201d grate will connect to the 3\u201d pipe using a 6\u201d catch basin and the 9\u201d grate will connect to 3\u201d pipe using a 9\u201d catch basin.<\/p>\n

        However, if say the flowerbed area had been 600 sq ft instead of 120 sq ft, the Rational Method formula in Step 2 would have increased the maximum runoff flow from 2.8 GPM to 14.1 GPM. The 3\u201d atrium grate that you had previously chosen would not have been adequate and a 4\u201d atrium grate would be required. In this case, you would need to use 4\u201d pipe for the drainage system. If you still preferred to use 3\u201d pipe, then a suggestion would be to use two adjacent 3\u201d atrium grates (each grate would then handle just over 7.0 GPM which is within its maximum capacity of 12 GPM).<\/p>\n

        Note:<\/strong> There are three common types of drainage pipe and fittings that are used. Tempo’s grates are designed to be used with all of them. Please refer to the Appendix at the end of this guide for more information on the different types of drainage pipes and the appropriate fittings.<\/p>\n

        STEP 7:
        \nSelect the grate colors.<\/h2>\n

        The most commonly used grate color for grass areas is green. When used with concrete applications, grey grates may be the most appropriate color. In other areas however, grate colors are more a matter of personal preference. In Table 7.1 below, you can see the different color options available.<\/p>\n

        Table 7.1<\/strong><\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
        Grate Description<\/td>\nAvailable Colors<\/td>\n<\/tr>\n
        3″ Round Flat Grate<\/td>\nGreen<\/strong> \/ Black<\/strong> \/ Sand<\/strong> \/ Grey<\/strong> \/ Purple<\/strong><\/td>\n<\/tr>\n
        3″ Round Atrium Grate<\/td>\nGreen<\/strong> \/ Black<\/strong> \/ Sand<\/strong><\/td>\n<\/tr>\n
        3″ Round Flat Grate and PVC Collar<\/td>\nBrass<\/strong><\/td>\n<\/tr>\n
        4″ Round Flat Grate<\/td>\nGreen<\/strong> \/ Black<\/strong> \/ Sand<\/strong> \/ Grey<\/strong><\/td>\n<\/tr>\n
        4″ Round Atrium Grate<\/td>\nGreen<\/strong> \/ Black<\/strong> \/ Sand<\/strong><\/td>\n<\/tr>\n
        4″ Round Flat Grate and PVC Collar<\/td>\nBrass<\/strong><\/td>\n<\/tr>\n
        6″ Round Flat Grate<\/td>\nGreen<\/strong> \/ Black<\/strong> \/ Sand<\/strong> \/ Grey<\/strong><\/td>\n<\/tr>\n
        6″ Round Atrium Grate<\/td>\nGreen<\/strong> \/ Black<\/strong> \/ Sand<\/strong><\/td>\n<\/tr>\n
        6″ Square Flat Universal Grate<\/td>\nGreen<\/strong> \/ Black<\/strong> \/ Sand<\/strong> \/ Grey<\/strong><\/td>\n<\/tr>\n
        9″ Square Flat Grate<\/td>\nGreen<\/strong> \/ Black<\/strong> \/ Sand<\/strong> \/ Grey<\/strong><\/td>\n<\/tr>\n
        9″ Square Atrium Grate<\/td>\nGreen<\/strong> \/ Black<\/strong><\/td>\n<\/tr>\n
        12″ Square Flat Grate<\/td>\nGreen<\/strong> \/ Black<\/strong> \/ Sand<\/strong> \/ Grey<\/strong><\/td>\n<\/tr>\n
        12″ Square Atrium Grate<\/td>\nGreen<\/strong> \/ Black<\/strong><\/td>\n<\/tr>\n
        18″ Square Flat Grate<\/td>\nGreen<\/strong> \/ Black<\/strong> \/ Sand<\/strong> \/ Grey<\/strong><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

         <\/p>\n

        STEP 8:
        \nDecide where to re-route this water.<\/h2>\n

        There are many options for re-routing the water that is collected in the grates and piping. Some of the most common applications for re-routing the water are to the street curb, to a storm water drain, to another landscaped area that can safely handle large volumes of water, to a French drain or to a storage tank that would allow for irrigation at a later time.<\/p>\n

        Let us assume that for this project, the run-off water will be re-routed to the street curb. Remember that the water must flow only downhill (even a small uphill section will prevent your system from draining properly). As the distance that the run-off water needs to travel is 100 ft, the recommended elevation drop from any grate to the discharge point must be a minimum of 2\u2019 or 24\u201d. (Minimum recommended slope should be 24\u201d per 100 ft or approximately 1\/4\u201d per foot). For optimum results this slope should be fairly uniform.<\/p>\n

        If the natural topography of the area to be drained does not have the necessary fall to meet the minimum slope requirements, you will need to dig a trench with the minimum slope required and then use a combination of low profile basins and catch basins, some of which will have one or multiple risers to make sure that grates end up at grade level.<\/p>\n

         <\/p>\n

        STEP 9:
        \nDesign piping network.<\/h2>\n

        There are 2 options for the 3\u201d piping network for the grass and flowerbed areas. These grates can either be plumbed inline or have two separate 3\u201d drainage pipes that are later connected into a single 3\u201d discharge pipe.<\/p>\n

        The plumbing for the drainage pipe from the concrete deck area will be a single 3\u201d pipe that runs from the 9\u201d basin to the discharge point.<\/p>\n

         <\/p>\n

        STEP 10:
        \nChoose the discharge end device.<\/h2>\n

        In our example, the ends of the drainage pipes will be cut flush with the street curb so no additional parts are needed. However, in many cases the drainage pipe terminates on the property and it is best to close it off with a grate or a pop-up relief valve to prevent debris or rodents from entering. This pop-up relief valve sits flush with the surrounding area and only pops up to allow excess water to discharge when the drainage pipe is full.<\/p>\n

         <\/p>\n

        APPENDIX<\/h1>\n

        Drainage Pipe<\/h2>\n

        There are three common types of drainage pipe to use.<\/strong><\/p>\n

          \n
        1. Corrugated Pipe is flexible and typically can make directional changes without the need for fittings. The advantages of this type of pipe are its flexibility and its ease of installation. The disadvantages are that it is hard to clean out (because of the corrugations), the connections are not very watertight and that the trench bed has to be very carefully sloped.<\/li>\n
        2. Sewer and Drain Pipe is a thin walled PVC pipe. This pipe needs Sewer and Drain hub fittings to make directional changes and joins. Because of its smooth wall, it is easier to clean and the trench bed slope and smoothness is less critical as this pipe will somewhat compensate for peaks and valleys.<\/li>\n
        3. Triple Wall Pipe is similar to the above but has a heavier wall and is thus sturdier. It also requires Sewer and Drain hub fittings to make directional changes. Because of its rigidity, the trench bed slope and smoothness is even less critical than with the Sewer and Drain pipe described above.<\/li>\n<\/ol>\n

          Fittings<\/h2>\n

          There are 2 common types of fittings that can be used.<\/strong><\/p>\n

            \n
          1. Sewer and Drain PVC hub fittings are used to couple the drainage pipe and change directions. The most popular and readily available 3″ and 4″ fittings are straight couplers, 90 degree, 45 degree and 22.5 degree elbows, straight and sanitary tees, 45 degree wyes and end caps. These fittings are solvent welded onto the pipe.<\/li>\n
          2. Single Wall corrugated fittings are used to couple the drainage pipe and change directions. The most popular and readily available fittings are straight couplers, 90 degree elbows, 45 degree wyes, tees and end caps. These fittings snap directly onto the drainage pipe.<\/li>\n<\/ol>\n

            <\/div>\n<\/div>\n

             <\/p>\n

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