Urban Hydrology - Hydrology - Lecture Slides, Slides of Water and Wastewater Engineering

Download Urban Hydrology - Hydrology - Lecture Slides and more Slides Water and Wastewater Engineering in PDF only on Docsity! Urban Hydrology for Small Watersheds 1 Docsity.com Simplified methods for estimating runoff and peak discharge for small urban/urbanizing watersheds • Ch 1 Intro • Ch 2 Estimating Runoff • Ch 3 Time of Concentration • Ch 4 Peak Runoff Method • Ch 5 Hydrograph Method • Ch 6 Storage Volumes for Detention Basins 2 Docsity.com Limitations • Accuracy decreases as complexity increases • Accuracy (+/- 25%) • Where possible, compare to gaged data • TR-20 (not TR-55) should be used if: – Tt > 3hours – Tc for any subarea > 2 hours – Drainage areas differ by a factor of 5 or more – Entire hydrograph is needed for detailed flood routings – Peak discharge time must be determined accurately 5 Docsity.com 6 Subareas 1 & 2 routed through 3,5 and 7 Subareas 3 & 4 routed through 5 & 7 Subareas 5 & 6 routed through 7 Proposed subdivision in 5, 6 and 7 Docsity.com 7 Table 5-1 Initial abstraction as a function of curve number Ia/P values are then calculated Docsity.com Worksheet 5b: Basic watershed data Priect Faliswood Lean Dyer County, Tennessee — [FY DW Pate 1/1/85 checkene: Elerecent Cl pevaipad | Frequency qr) 25 Shocked NM ™° 10/3/85 Subarea Basic watershed data used 1 Select and enter hydrograph times in hours from exhibit 54 2/ mm [sae | She | | lio 7lizalis.olia.2|i3.4[i3.613.8|14.0|14.3|14.6)15.0 [5.5 (hn ih) (mein) Discharges at sake preragreph times 3 1 |150|250] O10] o71 | 4] 4 6} 6) 8] 10) 113) 24} 49}100 149 2 | 125 |250| 010/056] 3| 4 6) 7) 8| Til 16} 32] 64} 110) 127 3 |050 |\200) 010\9033 |} 5| 5 8| 12) 21 41) 67) 98| 92| 60} 29 4 |075|200| 010/070 | 8| 9] nl y4| 20) 34) 2\i06| 172/192 1149) 81 5 |150|075| 010|0.66 | 21/28 | 50] 93] ne) 147/158] i54/ 127| 98 67| 44 6 | 150 | 075} O10) 112 | 36) 47 | 85/140 |200|249|269| 261/216 |166 | 4 | 75 7 | 125 0 | 0.10|\0.66 |169\187 |205)176| 140 108] 85) 69) 51| 40) 31) 24 Composite hydragraph at outlet 246 |284)366]433 |503|575 |636|686|720 | 701|631|529 iksheet Sa. Rounded as needed for use with exhibit 5. ‘er rainfall distribution type used. ydrograph discharge for selected tines is A, multiplied by tabular discharge from appropriate exhibit 5. Docsity.com Worksheet 5a: Basic watershed data Priet Faliswood ‘aio Dyer County, Tennessee | DW ™ 10/85 chackona: CI present (M) pevenpad | Frequency (yr) 25 Pheches NM 10/3/85 Subarea | Drainage) Time of Travel | Downstream Travel 24-hr Runoff Runedf Initial name area concen- time subarea, time rain- curve abstraction tration through: rames: summation fall number subarea. to outlet Am Ts Tt ET P cM Q Ama la laP imiz) (hry (hr) (hr) (ir (in (mit—in} (in) i jo30) 150, --| 3,5,7| 200 | 60) 65 2.35 O71 LOF? | O18 2 (020 | 125) --| 3,5,7 | 200 6.0| 70 2.80 | 0.56 | 0857 | O14 3 | 010 | 0.50 |0.50 5,7| 150) 6.0) 75 3.28 0.33 |O0.667 | On 4 1025 | O75) -- 5,7| 150} 60) 70 2.80 O7O | 0.857 | O14 5 {0.20 | 150) 1.00 7| 050 |) 60) 85 4.31 | 0.86 |0.353 |0.06 6 |040| 100) -- 7| 050 | 60 75 3.28 131 | O85? | O14 7 |020| 0.75\050| -- | 60} 90 | 485 | 097 | 0.222 | 0.04 Docsity.com Worksheet 5b: Basic watershed data Priect Fallswood tecies = Dyer County, fennessee |r DW Dae OWES checkens; Clpressnt OX) osvetopsa | Frequanay (im 25 a NM ™" 10/3/85 Subares Basic watershed data used 1/ Select and enter hydrograph times in hours from exhibit 5-11 2 Te [wee | | “° |12.7|12.8]13.0|13.2 | 13.4|13.6|13.8]14.0|14.3 [14.6 |15.0|15.5 (he) hi (m@in) Discharges at selected hycrograph tee a 1 | 150} 200) O10) O77 6] 6G 7 ii] 16| 24) 40 | 78 |122|155| 133 2 | 125) 200) 010/056 | 6| 6) 7| 9) 12) 20] 33)55|96 |132|132) 87 3 |.050| 150) 010/033 | 98] 9 14] 29] 58] saliogiio2| 74 | 46| 25| 16 4 | 075) 150) G10/070 | 73) 14) 19| 32] 63] ti4|}16qeO7 193 |143| 83) 46 5 | 150| 0.50) G10|0.86 | 51| 69) 117 | 167/205] 214|202) 175 |132 | 99| 7o| 48 6 | 100] 0.50) O10} 1.31 | 149|208) 331|407/393|329|255|195 |134 | 97| 69) 52 7 | O75 O| 0.10 | 0.97 |398)358/244 | 167|_19| 9o0|_72| 59 |48 | 40| 34) 30 Compscite hycrograph at cutlot 631 670 |739|820| 861 | 872|861|833|755/679|568) 412 Cs sheet Sa. Rounded as needed for use with exhibit 5. rainfall distribution type used. graph discharge for selected times is A,,0 multiplied by tabular discharge from appropriate exhibit 5, Docsity.com Green Roofs 15 Docsity.com Porous Concrete Pavers ¢ http://www.concretenetwork.com/concrete/p orous concrete _pavers/ if Docsity.com Pervious Pavements in Cold Weather • http://stormh2o.com/september- 2008/pervious-asphalt-concrete.aspx 17 Docsity.com Detention/Retention Basins 20 Docsity.com Ch 6 Estimating Storage Volumes for Detention Basins • Approximate method (+/-25% storage error) • Can be used for single and multi-staged outflow structures • Worksheet 6a-estimate storage volume given desired peak outflow • Worksheet 6b-estimate peak outflow given storage volume 21 Docsity.com Detention Outlet Structures • Single Stage (culvert or orifice) • Multi-Staged to handle different flows • Combination of orifices &/or weirs 22 Docsity.com Example 6-1 Single-Stage Outflow • 75-Acre Development • Developed Peak flow is 360 cfs (Q25) • Present channel can handle only 180 cfs w/o significant damage • Storage-elevation curve is given-see worksheet • Determine storage volume of a detention basin • Assuming a rectangular weir, determine the weir length needed to limit the flow to 180 cfs 25 Docsity.com Worksheet 6a: Detention basin storage, peak outflow discharge (q,) known Fae n [Date a Rabbinswille 5 ve | Tas > ei aa Tas Wo rk Dyer County, Tennessee tacked GE checkons’ Clerasort [i] cevaloped Single stage structure 106 — Figure 6-1 Approximate detention basin routing for rafal types 1A, I, and I 6 o 2 jo — u Ss gE 2 loz— oes i aa O gle ake 100 ale o 1. Dette: Cranage area meg Rainfall distribution Vr type (1, 1A, I, NN} -_! vt ; ; (Us 96 with igure 6-1 A _ 4 2 3 4 6 7 a Paak outflow discharge 7. Runot, 2. Peak inflow decharge (From 2, Frequency 4. Runot volume 1 YP _acn L 22 || 8. Peak inflow (Vy = GA 58.98) discharge q] ... B 9. Storage volumes, {trom worksheat 4.of Sb) vu, . 4, Peak outtiow eV (Yen discharge gy ....... 68 ‘ 10, Maximum storage Emax [IOE7] | 5. Compute 52 {trom plot) a Jy 2nd stage qo Includes 1st stage qo, Docsity.com Determining weir length • Flow=3.2*Weir Length*(Weir Head)1.5 • 180=3.2*Weir Length*(5.7) 1.5 • Weir Length=4.1 feet • Notes: – Weir head=max. storage elevation-crest elev. – A weir length greater than 4.1 feet would let more than 180 cfs into the drainage channel 27 Docsity.com