A Study of the Rainfall and Run-off from the Drainage Area Tributary to the Northeast Storm Drain, City of Pasadena Citation Sopp, Claude Wellington (1917) A Study of the Rainfall and Run-off from the Drainage Area Tributary to the Northeast Storm Drain, City of Pasadena. Bachelor's thesis, California Institute of Technology. doi:10.7907/n0yj-w120. https://resolver.caltech.edu/CaltechTHESIS:07152024-201041024 Abstract No abstract. Item Type: Thesis (Bachelor's thesis) Subject Keywords: (Civil Engineering) Degree Grantor: California Institute of Technology Division: Engineering and Applied Science Major Option: Civil Engineering Thesis Availability: Public (worldwide access) Research Advisor(s): Unknown, Unknown Thesis Committee: Unknown, Unknown Defense Date: 1 January 1917 Additional Information: Plates 20 and 21 are missing. Record Number: CaltechTHESIS:07152024-201041024 Persistent URL: https://resolver.caltech.edu/CaltechTHESIS:07152024-201041024 DOI: 10.7907/n0yj-w120 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 16553 Collection: CaltechTHESIS Deposited By: Benjamin Perez Deposited On: 16 Jul 2024 17:50 Last Modified: 16 Jul 2024 17:51 Thesis Files PDF - Final Version See Usage Policy. 18MB Repository Staff Only: item control page

THESIS A Study of the Rainfall and Run-off from the Urainage Area Tributary to the Northeast Storm Drain, City of Pasadena. by Claude w. Sopp. Class of Nineteen Hundred and Seventeen. Department of Civil Engineering THROOP COLLEGE OF TECHNOLOGY Pasadena, California 1917 l D1v1sioa of Subject Matter. Part I Introduction. Pa.rt II Rainfall. Part III Run- o:f'f . Pa.rt IV Recommendations. Part V Oonclusio:ns. Part VI Charts , Curves and Maps. 2 PART I -- I.NTROUUCTIOJ. The work,throughout the entire course of observations, was done under the supervision of the City En- gineer, Mr . n. v. Orbison, and the Civil Engineering 'Department of Throop College o-f Technology. In 'December the city installed a nstandard" Stage Recorder on the drain between Marion and Sierra Bonita Avenues. A com- mutator for the Gurley Current Meter. which makes contact every fifth revolution, made it possible to measure high velocities if the occasion had occurred. !he scope of the work was greatly limited by the nature of the rainfall during the winter months . While the total rainfall was nearly up to the seasonal average , no appreciable run-off oecurredo Most of the rains were of low 1ntensit7 and the heavy rains that did ocour were preceded by dry periods and consequently most of the preo1pitation was taken up by the ground . The maximum depth of flow recorded in the drain was 1.2 feet, and this was of short duration. "Oue to this lack of run- off no val~ ooity measurements were taken and the value of the coefficient of roughness (a) in Kutter 's formula could not be found . Since no velocity measurements could be taken , the velooity ou1'VeB were oaloulated from Kutter's formula using .013 for {n) and . 0159 for (s). The subject matter is divided into the following topics-- intensity of rainfall, durat i on of intensities, 3 relation between rainfall and ru.n- off, imperviousness of the soil, lag in time between maximum intensity of rainfall and the peak of the flood in the drain, and the re~ lation of the flood peaks in the branches to each other and to ,the ,hi~h water 1n the drain. The drain proper follows the north city limits from Marengo to Santa Rosa Avenues and then a southeasterly oourse across the city to the east city limits at San Pasqual and Allen Aves. The map on plate No. 2 shows the location of the drain. Below San Pasqual Ave. a contin- uation of the drain forms the county Rubio storm Drain No. 2. The tributary area extends in a strip thru Alt- adena e.:nd nearly to the foot of the mountains. The area tributa~y to the drain above the float gage is 2491 acres , nearly all of which is city or urban property. Below the float gage the Rubio Storm nrain Bo. l, with a drainage area of 2156 acres, joins the city drain, making with an additional portion of the oity a total ot 4904 aeres tributary to the lower part of the drain. The accompanying map , plate Bo o 2, shows the drainage areas. the channel is made of fairly smooth concrete and it is approximately trapezoidal in section. Cross sections at various points on the drain are shown on Plate N~ 1. The drain was designed for a rainfall of one and one-quarter in. per hr. and a run- off as given by McMath's form'Q.la Q • .BBvsl'i. , using .a as a coefficient of imper- Viousnesso fhe value of (n}. assumed for design in Kutter's formula was .013. 4 fhe geneFal method of proceedure was to oolleot ~ainfall data :from three gages j_n the drainage area. . while rainfall intensities wer·e taken from the reoord- i:og. tipping~bueket gage on the roof of the City Hallo With stage gages painted on the channel walls show~ng the height of water below the outlets of the tributary branohes and with the recording float gage near the lower 0nd, the relation betwe n the heights of water in the drain and intensities of rainfall was obtained. Since the q~antity of water flowing is a function of the gage heights . the relation between rainfall intensities and :run- off was found . The discharge was obtained by .measuring the area of a cross section of the channel and calculati!lg the velocity thru the section and then substituting these values in the formula Q : AV, After the discharge was found and with the amount of rainfall on the drainage area known, the percentage of imperviousness of the soil was calculated. 5 Part II -- Rainfall. The mountain range in back of Pa.sadena intercepts and chills the olouds thereby causing a greater precipitation in their vioinity. The record obtained by a single rain gage shows only the precipitation on a few square in. of surface and may not be representative of a considerable area. In order to obtain with more certainty the average p:reoipitation over the drainage area, several gages were used. Two u. s. weather Bureau Standard Rain Gages were used. This type of gage is eight 1nohes in diameter and has a .oapaoity for two inches of rainfall, and in connection with the overflow the possible capacity is 20 in. of rainfall. The gage is made so that one inch of rain- fall actually measures 10 inches on the measuring stick. One gage was located at Los Robles Ave . and Woodbury Rd. near the beginning of the drain, another was located at Throop College of Technology. ~hese two "Stamiardn gages. together with the recording gage at the City Rall and the government gage at the Mt. Wilson Toll n:ouse, oovered the area in a satisfactory manner. The attached oharts, Nos. 3 & 4, of oomparative rainfall show that as a rule t he gage a.t the Mt. Wilson Toll Rouse and the one at Los Robles Ave. and Woodbury Rd.• re- oord more rain than the other gages, located at the CitJ 6 Ball and at ~hroop College. The variation i s more pro- nounced if th& •rainf'all o:f Pasadena and Los Angeles be oompared .. The inorea.s e i n r a. i'nfa ll towards the mou.nt ... a.ins ie well shown in t he following table taken from the government reports for the months of January and Febuary. Date Jan 2 Mt. Wilson Pasadena Toll Rou.se. .os .48 . 37 ..... " 12 .33 " 15 .20 " 17 " 18 .33 " 19 1.31 " 20 Eoho Mountain. . 41 .48 ,06 1.14 - . 85 Total Feb .12 . 13 .12 " 17 .90 .70 " 18 n 19 n 20 " 21 " 22 1 . 04 u 23 ..... " 25 . 89 .31 .26 . 19 . 08 .95 1 . 28 .75 .715 The oomparative rainfall charts and the curves, ,, plates :Nos. 5 to 21 inclus ive, showing the :relation between rainfall and discharge, show that there is a great variation in rainfall over even the limited ares tributary to the drain~ . In plaaes, as at 7 A.M. on Jan. 20, the stage recorder -showed a sudden rise. while the recording rain-gage at the City Rall showed a nearly uniform intensity of precipitation. . . This :rise was due to a greater i ntensity farther nor"Gh in the drainage ares. . At another time, while the writer was working in the drain at the float gage, a sudden rush of water came down while there was no rain at the gage . At periods the rainfall is fairly uniform over the whole area, this being illustrated by the uniformity in variation . with a lag in tune, between the rainfall and discharge curves. Some exam~les of this variation tak- en from these curves are -- Feb. 22, at 2 A. M. and at 5 A.I~h; Jan. 1E;3. at 2 ?. . M. . and 11 P. M.. ; Feb. 21, at 10 P.u. and Feb. 25. st 2 A.M. No great intensities of rainfall occurred during the season; the greatest being .72 in. per hr . for five min• utos on Feb . 21, at 3 P . Isl. /mother of the greatest in- tens ities was at the rate of . 36 in. per hr. for 10 minutes on Fe~. 22, at 1:30 A.M. These i nt ensities are very low when compared to rates of 1 ,2 1:n. per hr. for 10 minutes which have been recorded in Pasadena . On the rainfall oharts, one small square indicates 8 that . 01 in. of rain fell during the interval !1.ti. ' t:tme sinee the previous square. For example, on plate .No. 16 beginning at 12 A. M. during the first five minutes • it was probably raining 'but tl1e bucket did not · fill and tip, while during the next 10 minutes the bucket tipped twice, indicating . 02 in of rain. Only where ·the · squares are eontinuous can intensities be calculated. The rainfall causing the maximum flow is the ·one that has the gree,test intensity, for a period of time equal to the time necessary for the water to collect i n the drain. An average of 11 cases showed the.t the high water in the drain appeared 15 minutes after a period of heavy re.il1. This would. indicate that 15 minutes was the time of collection. From curves of intensities . and durations plotted for Pasadena by Messrs. Carson and Ohamberle.in , an intensity of 1 . 3 in .• per hr . f or 15 min- utes woulcl cause tho maximum ran- off to be expeoted from Tho writer is of the opi nion that too muoh attent i on has been paid to intensities of shor t duration ; basins . these are only of value in designing eatoh- 9 Part III -- Run-off. Run-off depends on topography .. aharaoter and 1m.. perviousness of soil, drainage area , and intensity of rainfall. 'Due to the steep slopes and paved streets. the run- off in this district is ''flashy" in character. As st~ited before, there is e. lag of' 15 minutes between a period of intense rainfall and the flood peak in the dra,in, and when the rain stops the flow rapidly dies out o The float gage , or Standard Stage Reoorder , made by the Western Instrument Coo of Los Angeles, was in- stalled on a straight section with a uniform elope just above the intersection of the Rubio Storm Urain lo, 1. Two 4-in. pi pes, one from the bottom of the invert and the other from the toe of the wall , connect the stillwell with the drain. The float moves in an 18 in. tile chamber; water is admitted to the tile thru a two in. valve. Since this valve was throttled, the small rapid fluctuations were not ?ecorded. A gage was painted on the side of the drain to check the chart re s ding. The accompanying drawing, plate No. 22 shows the dimensions and. general arrangement of the float gage . Stage gages were painted on the ehannel walls in selected straight sections below branch outlets as shown on the map. G~e No. l vvas located just above Highlands st., gage :No . 2 about 30 ft. below Highlands st ., gage mo. 3 at liormandie st ., gage 10 . 4 just below 10 l.iaple . st ., while gs.ge .No. 6, or the float gage. wa s located between !fur.ion and Sierra Bon.i ta Aves. Cross sections o:f the ch·ain at the gag es are Bhown on plate No. 1. In this wa.y t he :run-off fr.om sections of the drainage area could be locslized and studied in more detail . Student assistants wer e to observe these gages, noting the ti.mo and. stage at 10 minute intervals. Since no flow o:f consequence occurred, no data was secured from these gages a Quite elaborate arrangements were made for measur- ing velooity.. Two methods were to have been u.sea., by floats, surfaoe and submerged; and the ourrent meter method. Weighted. bloaks were connooted to surface floats by e.n adjustable wire . The man starting the floats could, by observing the depths from a gage, set the submerged float at . 2 •• 6, or .8 of the depth. A timlng set, used by the police department and consisting of a buzzer and push button at each end of 300 ft wire , was to have been used in timing the floats. o of In order to measure the high velocit.tes expeeted, a commutator making contact every fifth revolution was used on the current meter . The ourrP.nt meter rs.ting curve was extended as a straight line , as shown in plate No o 23. To hold the meter in the high current a 30 l b. lead weight was seoured from Mr . J. C. -Oort,. the dist riot hydrogra.pher. This weight used in conjunction with a stay-line would. in the writer's opinion, work satis- ll ta.ctorily. At no time was there enough depth to sub- merge the meter. ~he theoretical mean velocity was calculated from Kutter's formula using .015, a.s assumed in design, for The formula is as the coeffieient of roughness (n}. follows:- ... V= 41.6 +. l t s -- slope - /! '4l • o t 0 .00281) !!_ s Jr - .0159 CO$ffieient of roughness = . 013 n; r l.811 0.00281 + $ n hydraulic radius for different depths. :L'he following table gives the properties of the drain at the float gage . 'Depth Area Hydraulic Radius Velooity 'Discharge .2 .34 . 096 2.5 .85 .4 1.23 .216 4.77 5.86 .6 2.55 .53 6.52 16.6 .8 4.16 .432 8.3 34.4 1.0 6.37 ... 648 9.77 62.2 2.0 18 .• 00 1.31 17.46 312. 3.0 29.96 1.89 22.36 670. 4.0 42.25 2.36 25.8 1090. 5.0 64.85 2.74 28.3 1500. 6.0 67.80 5.07 30.2 2050. 12 "Depth Area . 7.0 82 . lG . Rydra.u.l ic Radius Velooity "Discha rge 2650 Curves of these properties are shown on I' la,ces Nos o 24 , 25, and 26. The ourves of rainfall depth , and di seharge during the day , plates No . 5 to Eo. 2l inclusive , show clearly how the l'UXL- of:f varies with the r ainfall. The di scharge curves are plotted with oubio ft. per sea . as ordinate s and time as abscissa i therefore the area under the ourve, when multiplied by the value of one square i n. , gives the total disoha:r.ge in any given length of time. (One square in. equals 240,000 cub i c feet.} By taking the rainfall for a length of' time and the discharge for an equal ~p eriod beginning 15 minu'tes later, the perc ent- age of run- oft and imperviousness of the soil was calculated. The follow i ng table shows some results taken from the curves: -SHORT PERIOUS Bain:f'all Inches "'Duration Minutes Run- off Inches % Jan. 19 .os 125 . 0235 17.5 Feb. 20 . is 150 . 0168 9. 4 'Date n 21 .11 120 . 0103 9, 4 ti 22 ,13 85 . 0096 7. 3 n 25 . 09 85 . 0073 8.2 STORMS Rainfall Inohes Run-off Inches . 22 . 0372 16. 9 Js.n. 18-20 1.95 c296 15 . 2 Feb . 18- 22 2.27 . 267 11 . 8 24- 25 .79 .057 7 . 26 9 . 28 . 025 9.14 T)ate Jan. 15 1t Mar. In order to make a comparison, both ra.infall and ~ off are given in inches . The ~ercentage run- off thus found is quite small end it was characteristic of all storms during the winter. - 14 :Part IV ...,_ Recommendation:::. Before the next rainy season some means should be provided for removing the mud that enters the float chamber of the stage recorder. fhe opening of the two inoh valve is too small to be of any u.se. The effeet of high velocities in the drain on the ·,vater level in the still-well should be studied. . There is d.a nger of an eddy being formed at the slot in the floor of the drs.in . This oo u ld be remedied by ma.king the slot narrower . The rain gages should be so located the,t they can be res.d each day at 6 .A . !11 . Bead.ings t8.ken at other times cannot be comp~;1,rea. with the government gages,. One man should not attempt to measure velocities with the current meter. A note- keeper should wat ch for any debris coming down the drain and warn the instrument operator in time to avo id damaging the meter. 15 Part V -- Conclusions. The writer regrets that due to the lack of run.off not muoh information ws-.. s secured.. Since no velocity measurements were ta.k0n the value of (11) in Ku.tter's formula could not be found and consequently the work of Messrs. Carson a.net Chamberlain could not be checked . In a law-suit against the city it was contended that the drain synchronized the flood peaks from the tributary areas and made a larger flow in the drain . • Uue to the lack of run-off no data with regard to this oould be secured.