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Home My WebLink AboutDrainfield Calcs from Ray McDougal Project ACE Hardware IPM.Note Drainfield Calcs from Ray McDougal Project Joel Gray Dean_Martineau Joel Gray SMTP dean_martineau@comcast.net Drainfield Calcs from Ray McDougal Project EX /O=REXBURGCITYMAIL/OU=FIRST ADMINISTRATIVE GROUP/CN=RECIPIENTS/CN=JOELG EX /O=REXBURGCITYMAIL/OU=FIRST ADMINISTRATIVE GROUP/CN=RECIPIENTS/CN=JOELG Received: from mail.rexburg.org (10.10.0.3) by vaca.ci.rexburg.id.us (10.10.0.222) with Microsoft SMTP Server id 8.1.436.0; Fri, 4 Oct 2013 14:45:36 -0600 X-ASG-Debug-ID: 1380919534-02b3ec7e6e1496c50001-awiCdn Received: from qmta07.emeryville.ca.mail.comcast.net (qmta07.emeryville.ca.mail.comcast.net [76.96.30.64]) by mail.rexburg.org with ESMTP id uf7XccP09tS0zlUx for <joelg@rexburg.org>; Fri, 04 Oct 2013 14:45:35 -0600 (MDT) X-Barracuda-Envelope-From: dean_martineau@comcast.net X-Barracuda-Apparent-Source-IP: 76.96.30.64 Received: from omta24.emeryville.ca.mail.comcast.net ([76.96.30.92]) by qmta07.emeryville.ca.mail.comcast.net with comcast id Z1CY1m0011zF43QA78labd; Fri, 04 Oct 2013 20:45:34 +0000 Received: from sz0100.ev.mail.comcast.net ([76.96.40.137]) by omta24.emeryville.ca.mail.comcast.net with comcast id Z8la1m0072xZMJ48k8lazd; Fri, 04 Oct 2013 20:45:34 +0000 X-Barracuda-BBL-IP: 76.96.30.92 X-Barracuda-RBL-IP: 76.96.30.92 Date: Fri, 4 Oct 2013 20:45:34 +0000 From: Dean_Martineau <dean_martineau@comcast.net> To: joelg@rexburg.org, dean_martineau@comcast.net Message-ID: <26256620.3469505.1380919534053.JavaMail.root@sz0100a.emeryville.ca.mail.comcast.net> Subject: Drainfield Calcs from Ray McDougal Project MIME-Version: 1.0 X-ASG-Orig-Subj: Drainfield Calcs from Ray McDougal Project Content-Type: multipart/mixed; boundary="----=_Part_3469503_280656349.1380919534052" X-Originating-IP: [::ffff:24.10.141.214] X-Mailer: Zimbra 6.0.13_GA_2944 (zclient/6.0.13_GA_2944) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=comcast.net; s=q20121106; t=1380919534; bh=x5lLs1KqznZ4bWJ3q4jiV/2gpBs3rlPlCukjUm6OABU=; h=Received:Received:Date:From:To:Message-ID:Subject:MIME-Version: Content-Type; b=hYQxH71v+i/2XQ4f96z1ye4DSaAnZxhqZjr1UUcccPorpk3WdHQEwYVq+lFh311JG roUyjRgJmqYvvhIAtonqBkKb0ep+qwHa9h4bKQdegPEeRPO+8BSQvUi8gOIYNwzknu Ql7w+Wpy0EWE4IWRy4+E6HVlIJ6HCKwaLdGlM0KcjUnKR8f04Kb632fvPbmK0mgSDH +5xAyniuGz1BGHmx2HM+Dfch06KeUxUiYktalJuFSoL6O9mQ67SWzmtDwY5N1LcThl U06DmpMqxnaiErkymBnK9hx71DmlXjs0LaotwG5+7NOa4gkoa0zJNdiSJ4Rsd4ejcZ Qni8X0hpXHcZA== X-Barracuda-Connect: qmta07.emeryville.ca.mail.comcast.net[76.96.30.64] X-Barracuda-Start-Time: 1380919534 X-Barracuda-URL: http://10.10.0.3:8000/cgi-mod/mark.cgi X-Virus-Scanned: by bsmtpd at rexburg.org X-Barracuda-Spam-Score: 0.00 X-Barracuda-Spam-Status: No, SCORE=0.00 using global scores of TAG_LEVEL=3.5 QUARANTINE_LEVEL=1000.0 KILL_LEVEL=4.0 tests=HTML_MESSAGE X-Barracuda-Spam-Report: Code version 3.2, rules version 3.2.2.141175 Rule breakdown below pts rule name description ---- ---------------------- -------------------------------------------------- 0.00 HTML_MESSAGE BODY: HTML included in message Return-Path: dean_martineau@comcast.net Dean_Martineau SMTP dean_martineau@comcast.net Joel Gray; dean_martineau@comcast.net Drainfield Calcs from Ray McDougal Project Joel, Please review the attached revised drainfield calculations. I received some suggestions from Logan City Engineers, Lance and Cameron who thought as you do, that the rational method is a weak tool for this particular application of drainfield designs. Their concern was the large area of an impervious roof and the short time of concentration. Although the rational method usually works well for areas of 1-acre or less, other methods should be considered for this project. They suggested using a "spread sheet" approach where flow accumulation on the roof is compared to drainfield percolation in 10 minute intervals. Using a 0.9 inch i-value for one-hr gave me more realistic results. After a few iterations, I discovered that 4 StormTec units would work okay. I also built-in a safety factor by using a percolation rate in the drainfield of only 6 inches/hr. rather than 8 inches/hr. Please call me at 435.563.9462 or email me if you have questions. Thanks Dean <26256620.3469505.1380919534053.JavaMail.root@sz0100a.emeryville.ca.mail.comcast.net> Drainfield Calcs from Ray McDougal Project.EML joelg@rexburg.org Internal http://10.10.0.3:8000/cgi-mod/mark.cgi 1380919534 qmta07.emeryville.ca.mail.comcast.net[76.96.30.64] 76.96.30.92 by bsmtpd at rexburg.org Drainfield Calcs from Ray McDougal Project 76.96.30.92 76.96.30.64 0.00 No, SCORE=0.00 using global scores of TAG_LEVEL=3.5 QUARANTINE_LEVEL=1000.0 KILL_LEVEL=4.0 tests=HTML_MESSAGE Code version 3.2, rules version 3.2.2.141175 Rule breakdown below pts rule name description ---- ---------------------- -------------------------------------------------- 0.00 HTML_MESSAGE BODY: HTML included in message 10 vaca.ci.rexburg.id.us 1380919534-02b3ec7e6e1496c50001-awiCdn dean_martineau@comcast.net v=1; a=rsa-sha256; c=relaxed/relaxed; d=comcast.net; s=q20121106; t=1380919534; bh=x5lLs1KqznZ4bWJ3q4jiV/2gpBs3rlPlCukjUm6OABU=; h=Received:Received:Date:From:To:Message-ID:Subject:MIME-Version: Content-Type; b=hYQxH71v+i/2XQ4f96z1ye4DSaAnZxhqZjr1UUcccPorpk3WdHQEwYVq+lFh311JG roUyjRgJmqYvvhIAtonqBkKb0ep+qwHa9h4bKQdegPEeRPO+8BSQvUi8gOIYNwzknu Ql7w+Wpy0EWE4IWRy4+E6HVlIJ6HCKwaLdGlM0KcjUnKR8f 04Kb632fvPbmK0mgSDH +5xAyniuGz1BGHmx2HM+Dfch06KeUxUiYktalJuFSoL6O9mQ67SWzmtDwY5N1LcThl U06DmpMqxnaiErkymBnK9hx71DmlXjs0LaotwG5+7NOa4gkoa0zJNdiSJ4Rsd4ejcZ Qni8X0hpXHcZA== [::ffff:24.10.141.214] joelg@rexburg.org 00000003244acdd4-17f9-4301-a47c-568fd1a47a85@rexburg.org/o=RexburgCityMail/ou=First Administrative Group/cn=Recipients/cn=joelg Joel Gray EX /O=REXBURGCITYMAIL/OU=First Administrative Group/cn=Recipients/cn=joelg joelg@rexburg.org Joel Gray dean_martineau@comcast.net SMTP dean_martineau@comcast.net dean_martineau@comcast.net dean_martineau@comcast.net Drainage Calcs Rexburg Comm Roof3.doc DRAINAGE CALCULATIONS Given: Calculate the volume of flow collected from the roof of a building in Rexburg, ID. Coefficient of runoff for a roof = 1.0, use portions of the Rexburg, ID unit hydrograph which represents a 25 year storm, 1-hr duration (i = 0.9 in/hr), area = 11,726 sf. Required: Calculate the total drainage vol. to be removed using downspouts. The drainage zone consists only of the roof area. The area of the roof = 11,726 sf. From the unit hydrograph, the depth of water on the roof would be approx. 0.9 in./hr, which would be a volume of 880 cf. In order to size the drain field, (2) methods of volume calculations will be compared on the next sheet. Note: it would be wise to use larger downspouts than calculated in the event the pipe inlets become clogged by leaves. Perhaps even a “lamb’s tongue” should be considered (to act as a safety valve to prevent catastrophic roof failure) if the owner anticipates the drains will not be properly maintained. (continued) Design the drain line that will carry the runoff from roof level to the drainfield (storm water interceptor). Note: The downspouts (with funnels) on the roof, and the drain line at ground level must be capable of accommodating a flow rate equal to that of the rate rainfall collects on the roof (worst case) From the Rexburg unit hydrograph, use 2.9 in. (i-value) for a 10 min. duration storm to determine safe pipe capacity. Max. flow (Q) for a peak 10-minute duration storm, = [(1.0) (11,726 sf)] (2.9 in/hr/12)ft (7.48 gal/cf) = 21,200 gal/hr, (or 353 gpm, or 0.79 cfs) Try using a 6” dia. PVC pipe, then, Q = AV, and Q = total flow of the pipe (cfs), A = area of the pipe (in sq. inches), and V = the vel. of the flow (ft/s). first, solving for the velocity, V = 1.49/n R 2/3S 1/2, n = roughness factor, R = hyd. radius (d/4 for round pipe flowing full), S = slope, V = (1.49/0.011)(0.50/4)2/3 (0.57)1/2 = 25.4 fps (max) therefore, Q = AV, and A = Q/V, A = (0.79)/(25.4) = 0.03 ft2, the area of a 6” dia. pipe is (3.14d2/4) = 0.20 ft2 , 0.20>0.03, ok. Note. With high velocity flow, there will be turbulence resulting in a higher Reynolds number, and a flow less than the calculated value. Therefore, do not use a smaller dia. pipe than 6”. Design the drain field: Calc. the size of the drain field needed for the runoff using (2) methods: 1) a 24 hr duration storm with an i value of 1.92”/24 hrs, and 2) size the drain field needed to handle 0.9” of rainfall per hour from the roof. Use the most stringent condition for the calculation of the design. Both sets of calculations use the StormTech system. The percolation rate is 8”/hr for the soils. Try a drain field with usable dimensions (below the structural road section) of 15.6’’ x 12’ x 3.5’ deep (using (4) SC-740 units) 1) For a 24 hr. storm in Rexburg, use 0.08 in. per hr (i-value) or 1.92” in/24 hr. vol. needed according to the design standards = (1.92 in/day)(1 ft/12 in)(11,726 sf) = 1,876 cf per day from the roof area. The max. perc. area that could be used would be the bottom + the area exposed to free water up to 3.5’ max. depth, (15.6’x 12’)sf + 2 (15.6’x3.5’ + 12’x 3.5’)] sf = 380 sf, The max.vol. provided = 380 sf(8 in/hr)(ft/12 in)(24 hr) = 6,110 cf per day, 6,110 >1876, okay 2) The second method of calculation uses a 1hr duration storm with a 0.9 in/hr (i-value). This method compares the volumes of rain on the roof vs. the volume percolating into the drain field in 10 min. intervals. (10 min = 1/6 hr, 20 min = 2/6 hr, etc.). Provide a safety factor by allowing i = 6/12 ft/hr (0.5) and not 8/12 ft/hr. At end of Vol. on roof Perc. Area Perc. Avail. Net Difference 10 min. (1/6)(880) Bottom only (0.5’)187sf 147 cf – 94 cf = 147 cf = 94 cf = 53 cf 20 min. (147+ 53) cf Bot. + (2/6) 0.5[187+2/6(190)] 200 cf – 125 cf = 200 cf sides = 125 cf = 75 cf 30 min. (147 + 75) cf Bot. + (3/6) 0.5[187+3/6(190)] 222 cf – 141 cf = 222 cf sides = 141 cf = 81 cf 40 min. (147 + 81) cf Bot. + (4/6) 0.5[187+4/6(190)] 228 cf – 157 cf = 228 cf sides = 157 cf = 71 cf 50 min. (147 + 71) cf Bot. + (5/6) 0.5[187+5/6(190)] 218 cf – 172 cf = 218 cf sides = 172 cf = 46 cf 60 min. (147 + 46) cf Bot. + sides 0.5[187+6/6(190)] 193 cf – 189 cf = 193 cf = 189 cf = 4 cf 878 cf Total volume of stormwater over 1 hr. on roof = 880 cf, total percolation over 1 hr. in drain field = 878 cf (applying the safety factor). The first column is not added because much of the flow is carried over from the previous row and is counted more than once. 880 is approx. 878, okay The greatest difference between the net rainfall vol. on the roof vs. vol. of percolation in the drain field is 81 cf (which is about 21% of the capacity of the drain field when the safety factor is applied), therefore 79% of the perc. area is available for variations in the flow. Four StormTek units are adequate for the design, and method 2 calculations are more stringent and will be used. The designed system would consist of a rect. hole with (2) stormtech sc-740 chambers lying side by side (12’ overall), and (2) end to end (15.6’ overall), for a total of 4 units. Backfill the hole according to the Stormtech specification using AASHTO M288 class 2 non-woven geotextile. over the rock, and a structural pavement pavement design provided by StormTech. 3 .doc Draina~1.doc Drainage Calcs Rexburg Comm Roof3.doc application/msword