oe) pict ici desma oan Oa AA nde b meV 19 Le i ll THESIS. THE SIGNAL HILL STORM DRAIN LONG BEACH, CALIFORNIA. 1915. By Re V. PEARSALL. THESIS THE SIGNAL HILL STORM DRAM. Long Beach California is a city of thirty-two thousand inhabitants which has enjoyed a very rapid growth. Property values have had a corresponding increase, resulting in scat- tering the population and making urgent the need of a vast amount of public improvement, among the most important of which is a system of storm drains. The city has a south frontage on the Pacific Ocean with the San Gabriel river dividing north of the city, leaving low lands to the east amd west. Between the city and the plain on the north is high ground known as Signal Hill. The San Gabriel river is a mere creek during the sunmer months, but during the winter it is subject to serious floods becoming a raging torrent, miles wide in places. Immense quantities of silt are carried by thesé floods to the harbor of Long Beach and that of Los Angeles, adjoining on the west. So serious has this damage become that it is proposed to divert the flow of the San Gabriel river to the east of Signal Hill and Long Beach, thus disposing of a serious drainage problem and making industrial property of land now anmually submerged. A secondary benefit resulting from the diversion of the San Gabriel river is that it provides a splendid outfall for draining a basin lying just gouth of Signal Hill. This area has no natural drainage and contains approximately twenty-five hundred acres and lies partly out and partly within the corporate limits of Long Beach. Each year a lake forms in this basin 403356 Ol —— - and its size has been increasing until now it covers approx~ imately one hundred and twenty acres, appearing in January and after dwindling to about two acres in September, remains until the next rain in December. Doubtless the impervious area has been increased very much by the growing city and increased run-off accounts for the quantities of water accun- ulating in the basin. This pond is stagnant and a menace to health, yet surrounded on all sides by property selling at two thousand dollars or more per acre. There appear three methods of draining this basin:~ Draining to the ocean on the south; To tide lands on the east; or To the low lands on the west. The characteristics of the basin are shown on the attached contoured map which discloses a steep water shed of five-hundred and forty-five acres on the north and a shed of nineteen hundred and twenty-five acres on the south draining to a pond between whose bed is eight and six tenths fee@ above city datum. This datum plain is sevensnd sixtenths feet above mean lower low water or about the highest high tide line. Tracks of the San Pedro Los Angeles and Salt Lake railway company are carried on a fill through California avenue, thus dividing the southern water shed. Drainage of that portion lying west of California avenue three hundred and seventy acres in area presents a sep- arate problem as its storm water is intercepted before reaching the lake and is easily carried to the low lands on the west. Outside of about four hundred acres lying south of Seventh Street the entire region is sparcely inhabited and the streets are oil dirt roads without walks and gutters. The south shed et Lv ge has a top soil of heavy loam one to two feet thick below which lie alternate layers of yellow clay and sand. The soil on the north slope is lighter and with equal slppes would have a much greater rate of percolation than that on the south. Table one gives a record of rain fall for Long Beach during a twenty year period. This table was prepared to show the conditions which a storm water sewer would have to meet and shows a& maximum rain fall of three and eighty~-three hundreéths inches. The severest storms of each gear arelisted and show periods of daily rains and is intended for use in providing overflow area. The season maximum seems to lie arround twenty inches which amount has been approached during the years 1914-1915. TABLE NO. l. Rainfall record for Long Beach, Season Precipitation Precipita- Precipitation during severe in inches. tion for storms. One day. Days Inches .« 18 94~1895 15.14 £042 13 4.12 1896-1897 19.96 3283 3 4.39 1897-1898 6-06 1.20 4 2077 1898-1899 6-51 1.50 2 2eo9 1809-1900 9.63 1.12 3 1.59 1900-1901 12.70 2e71L 5 4.25 1901-1902 9.47 2eld 3 3e42 1903-1904 7.15 1.78 1 1.78 1904-1905 15.55 2258 6 4.73 1905-19 06 20.88 1.85 2 2-298 1906-1907 14.69 2e20 5 2.98 1907-1908= 10.04 1.49 6 4.29 1910-1911 13.19 1.06 2 2255 1911-1912 7256 1.02 9 4.08 1912-1913 8.14 2-00 3 4.20 1913-1914 17.27 280 2 3.85 1914-1915 2—.15 2 85 2 35236 Additional rainfall data was obtained from the United States weather observer in Los Angeles ani his records show mamzimum rainfall for periods of less than twenty-four hours. Table Number two is taken from his report and shows a maximum of one and nine tenths inches for one hundred minutes which figure I have used in my calculation. TABLE NO. 2. Excessive precipitation at Los Angeles, Cal., for the 15 years, 1899-1914. Duration. Amount in inches. 5 minutes 056 7 minutes e51 10 minutes ~66 15 minutes e81 20 minutes 85 30 minutes 112 60 minutes 1-51 100 minutes 1.90 Amount and velocity of run-off are rather indeterminate quantities but of prime importance in this subject. The problem is relatively simple once these factors are determined. The percentage of run-off was found by actual measurement in the pond with allowance made for evaporation and percolation. To measure this water I first found the area within each one foot contour lying within the flooded district. These areas am the method of computing the voluma are shown in table number three. ~~ 5 TABLE NOS. Volume of Lake. Contour. Area-SqeFt. Area Times Difference Difference depth in Areae in area x 1/3 distance bet. contourse 9 6125 6125 10 21600 43200 15475 5160 12 79250 79250 57650 38430 13 144000 144000 64750 21580 14 281000 281000 137000 45670 15 1112500 1112500 831500 277170 16 2998800 5997600 1886300 628770 18 5072400 | | 2073600 1382400 7663600 2399180 7663600 208.0 Acre feet. 10062780 43560 ) The volume of water shown 208 acre feet is that of the lake with the surface at contour 18 which has been its approximate level in February 1914-1915. The maximum area of this lake as I before mentioned is approximately one hundred and twenty acres. Its life is from December to September or nine months. In February 1915 the surface of the leke was at elevation 17 when the accumugated rainfall wasl15.5 inches. This water had been accumulating since the last of December 1914 and would practically all be gone by the first of September. Evaporation statistics for Los Angeles in 1887-1888 are used in the following calculations. The average area of the lake while receeding was sixty acres and the time of receeding was six months. Evaporation for these six months was seventeen and eight-tenths inches per square foot or a total of three million eight hundred and sixty eight thousand cubttc feet. ro ~6— This evaporation had been taking place during the two months the lake was forming or 60 x 43560 (Area) x .36 (Evaporation) equals 941000 cubic feet. Now the contents of the lake 9062000 cubic feet minus 4809000 cubic feet or 4253000 cubic feet repre- sents percolation into the ground in six months or the average rate per square foot of surface per month was 34 inches. Assun- ing this rate to hold while the lake was forming we find 1524000 cubic feet to have percolated away previous to the time the lake contained 9062000 cubic feet and has had 941000 cubic feet evap- orate. The average area of the lake has been 2613000 square feet so the direct rainfall has been 3376000 cubic feet. Adding evap- oration and percolation and deducting direct rainfall gives 8151000 cubic feet as the run-off from 2470 acres and 15.5 inches of rainfall. This run-off is only 6% of the rainfell which small ratio is explained by poor drainage into the lake aided by heavy local percolation and evaporation. Soon after drainage is pro~- vided streets will be improved and the run-off will increase rapidly but will probably not exceed 20% within ten years. 4s before stated there are three feasable methods of drain- ing this area, directly south to the ocean, east to tide lands, or west to Cerritos Slough. Rapid run-off from the north water shed makes it necessary to have a trunk sewer at the foot of this Slope. To put in a collecting system on the south slope designed to intercept the run-off would thus be robbed of the advantage of a shortened main sewer and since such a system not o&ly calls for laterals but demands that street improvements be made I have decided to run all water to a reservoir located at the low point of the basin and bring the water by surface drainage to this point. As streets are improved new collecting sewers my be installed and the system now built will be in place to handle overflows where the future sewers may prove inadiquate. A drain to the south would be placed in Cherry Street because of an off-set in Walnut street which would make necessary tunneling under private property where such privileges would be hard to obtain. Cherry street is paved and any sewer placed in this street would need to be of a permanent nature so any trunk line installed shouad be of sufficient size to accommodate the entire basin. A plan and profile of this route and drain are shown on drawing Noe 2. Hawksleys formula gives an approximation as to the size of drain needed to carry the entireaffluent. This engineer designed some of the min sewers of London and Brooklyn which gives his formula a standing, it is- Log(d)equals 3 log(A) plus log (N) plus 6.8 divided by 10. D equals the diameter of the sewer in inches. NH equals distance in feet in which the fall is one foot. A equals area in acres. An outfall at the ocean would be located at an elevation approximating <3 and with an approximate length of 11500 feet with inlet at about 5 (N) would equal 1425. (A) equals 2470. The diameter thus becomes 8feet and 7 inches. The maximum cut would be 50 feet and the average 29 feet. Buerkli gives as a result of his experience the following formula for the storm flow. F equals er (Eh f equals proportion of run-off. ¥ equals the flow per acre and cubic feet per second. S equals the average slope. ‘A equals the area of the district in acres. oe ~G~ r equals the rate of rainfall in inches per hour during period of greatest intensity of rain. For subarban districts roughly paved he advises using a value of(f) of.44. (A) is 2470 and (r) is 14. (S) equals 2 for 1555 acres and 75 for 545 acres. This formula gives a value of (F) equal to 180 cubic feet persecond. Assuming the sewer to be concrete and using Cutters formula with (c) equal to 113 we get a value of (ad) equal to 7 feet and 2 inches. A formula easy to apply is vouched for by Adams of Brooklyn and is;:= L 1/6 D squats Soe} / Q equals Acfes for rainfall of 2 inches per hours “Lledo ° D equals dhameter of the sewer in feet. L equals length of the sewer in feet. H equals the total fall of the sewer, This gives a value of(D)equal to 11 feet and 6 inches. An application of HcMaths formula shows a diameter of 9 feet and three inches to be required. From these computations I feel safe in saying that a pipe 8 feet in diameter will be necessary. The installation of such a pipe will be expensive because of constructing an outfall in the open ocean, excessive cut, and replacing a large amount of pavement. t a me as SD a ———E—E—————ES eS ; : i t 9 Lo Le ae a E i Ss SS ~ Ee as RET \ | 5 OE SRN POPE TS = / . : ie ee ee . ; ; 3 = 1 H N ; i 1 ; —— ——————— J CF SS ATS SS AP, OT LL ea 2 nee a ee Se ae een cee part LA ; 1 ; = | a = i | i < Se os ; <1 re ~ i ~— A : 2 = SS SS SS = = } Ld z mS wD a=) BE - ae at ce ee ey, 777d Vee Oe da sees SS TRY ee Se Se Vw LE, eae FILL ee a = = ; Se + 7 1) A LO A LL Oa LLL MF STL A To pore Sate aso } ALE SEAKVKOlA? #k< SETS laches #17 £4 Claw S JIE 009 CvOQ/c feCCK oF 1335 7OIGOI Ceb/c Leer i POR MAAS Og ny A ~“ ~e nina iin ini i g : i PLA | : BPECTANGULAP? DRAIN FOU? FLEET = = + Lea 6 es NE We re FLATEL 5 PIE CTANGUL AP? PP?AUM FOU? FLED BY THREE LEED -7HPL 2 \ == = rie Vela ae ee Ve ata Zz ; Fat Se ee ee = . ; 7 = 2 = : = : —— wee = ; = = i —— eS == Seas ee Be ES eet ore Pe ae wees ee eS SS 6 0 =e Free aT 2 7 SP ES ES CA SE OS OE EE | 9S a < a 2 ee ee = =" da LA a VP Ea FT ae YL SLATE FA a et SE SEAVOV? Kc SES laches t12 £94 Coidrs : IFEOO? Cvivce Seer o7 : 4897090 Cvblo Feexr Ge LIE CTANGULILT? DAN FO? FEE FT r2 noes aon ee Sees eee ye =| ig 41 oat Mee ba koe y= nade ee is bh ka Bel A IO? laches tf2 29 flowPs a Y THAEE FEET Pe, ONL al 2 ae ree Pee Ee a aa od 4 oe See coo Soe Sis ae J ~l4— The diagram shows the drain to be adequate and that the water level of the reservoir will begin to receed at about the time the rain ceases. Water would continue to reach the reservoir for 13 hours and 15 minutes but in 28 hours after the storm the reservoir would be empty. This assumes the most adverse conditions at the outfall thus providing an additional factor of safety. The reservoir used in this design calls for an excavation of 58000 cubic yards this earth will raise all the lew lands adjacent to the reservoir to elevation 15 and provide 21 acre feet additional fill. Since this locality is neither inhabited nor cultivated several blocks may be graded with this waste dirt thus raising them above the danger zone. This excavation may be handled very cheaply and theadditional cost of enlarging the reservoir is less than that of increasing the cross-section of the drain. Lack of head room makes necessary the use of a box section over a considerable portion of the work and the section is continued uniform throughout since it obviates the danger of a reduced flow and consequent silting at the points of change in section. The walls of the drain are designed as simple slabs though a few longitudinal rods are introduced and the reinforcing carried continuous through the top and sides. Stresses are computed for a back fill weighing 120 pounds per cubic foot and the following table computed by Marston & Anderson was used in this work. In the streets a coneentrated live load of 8670 pounds is used and represents the wheel load of a ten ton read roller. Beneath the right of way of the Pacific Electrgco Railway a surface load of 650 pounds per square foot is used and beneath -~15— the Salt Lake Railway a load of 1500 pounds per square foot is used, these representing loads caused respectively by the heaviest interurban electric car and largest locomotive. In crossing private property a live load of 350 pounds per square foot is used and beneath sidewalks 200 pounds per square foot. . TABLB NO. 4. Approzimate maximum loads in pounds per linear foot on pipe in trenches imposed by saturated sand fill- ing weighing 120 pounds per cubic foot, BREADTH OF TRENCH FOUR FEET. Depth of fill above pipe. Pounds per linear foot. 2 880 4 1280 6 2580 8 2980 LO 3500 12 3980 14 4390 16 4'750 18 5060 20 5330 Le 5570 24 5780 26 5970 28 6140 30 6260 TABLE NO. 5. Proportion of local superficial loads on back- filling which reaches the pipe in trenches with dif- ferent ratios of depth to width. SAND AND DAMP TOP SOIL. Ratio of depth of fill Ratio. above pipe to width of trench, 1.0 059 200 o 35 520 o21 ( TABLE NO. 5. CONTINUED ). 1.5 046 205 ent 46 eo l2 5. 207 6. 004 8. 002 10. eOl The trench width is uniformly 5 feet. The material throughout is such that side forms will not be necessary and but light timberin; will be needed. In placing the floor slab 2 inch planks may be mbeded at the sides thus forming seats or shoulders for the side walls and assisting infloating and bringing the floor to perfect grade. I also suggest placing greased wooden pins on these planks before being ambeded thus forming sockets to receive the rods,re- inforcing the sides and top. The form Work for this design is the simplest possible. There are no intricate stresses to be considered in the design and no difficult steel spacing nor placing. The elements, quantities and number of feet of each section are shown in a table on drawing number 4. The location of these sections are shown on drawing Noe 3. The inlet is placed near the center of the reservoir and details of its construction are shown on drawing No. 4. Its location is chosen with a view of haYing the heaviest debris deposited before reaching the drain. The mouth of the drain is protected by a number of small of palvanized pipes fixed in the concrete of the upper slab and slightly embeded in the lower slab. Since the reservoir will seldom contain water it may be used as a small park in which case the mouth of the drain would need to be covered to keep children out. These rods may be easily lifted mam a. ~17- up permitting entrance for cleaning thus obviating the need of an extra man hole. Since there are neither curbs nor sidewalks along the south side of State Street from Locust Avenue West the drain is here carried 5 feet from the property line. This reduces the slab sections very materially as the drain here lies very near the surfacé thus necessitating heavy construction if placed in the roadway. The top of the drain comes just below the gutter grade of the intersecting streets and will form a splendid sub-grade for thhe sidewalks when built. lanholes in this section are placed in street or alley intersections as property owmers will seriously object to a manhole cover in the sidewalk in front of their property. The outfall is placed on a line with the east face of the opening beneath the present State Street bridge. This insures an outfall into rapidly flowing water without danger of being damaged by the stream or of having a sand bar form in front af it either of which injariew might occur were the outfall located elsewhere.