Hydraulic Model Study of Bicygle-Safe Catch Basin Grates an Interim Report

t I HYDRAULIC MODEL STUDY OF BICYGLE-SAFE I CATCH BASIN GRATES 'rI AN INTERIM REPORT CITY OF LOS ANGELES BUREAUOF ENGINEERING I DRAINAGESYSTEMS ENGINEERING DIVISION I HYDRAULICRESEARCH LABORATORY 24OO NORTH ALTMAN STREET LOS ANGELES , CALI FORNIA 9OO3I I TELEPHONE (2t3) 225-er92 I I t I I I DONALDC. TILLMAN CITY ENGINEER I AARON AARONS DIVISION ENGINEER I DRAINAGE SYSTEMS ENGINEERING DIVISION I I r975 I 7 I I I I ABSTRACT T A hydraulic model investigation was conducted to quaL- itativeLy compare the hydraulic characterietLcs of 22 proposed bicycle-safe gratings with two types currently in use by the city I of T,os Angeles. Four of the gratings.were selected for further guantitative testing. This is an interim report presenting the T preliminary results of the qualitative tests of 24 grates and limited quantitative il tegts of the four grates. A description and sketches of all of the grates teeted are included in Appendix III. I Selection of the gratings to be tested was based upon bicycle safety, pedestrian safety, compatibility with existing I catch basins, hydraulic efficiency, and econonry. Three of the four grates tested were reconmended for use in replacing any t city grates that might be hazardous to bicyclists. one of the grates was selected as the standard for use by the city of tog T Angeles. I The grates \rere tested in a 1:5 ecale model of one- half of a tlpical City street (60-foot (13.3 m) right-of-h'ay I with a 40-foot (12.1 m) pavement width). street slopes tested were 2, 4, 6,8, lO, 13, and L6%. Depthe of flow upstream of the grates varied from 3 to 8 inches (7.6 to 20.3 cn). Ifirdraulie capacity charts are presented for the four gratce tegted quantitativery along with the results of the qualitative tests ot 24 gratcs in addition to an open hole. I I I t I ACKNOVfI,EDGMEhITS t This research study was conducted by the staff of the nydraulic Research Laboratory of the City of Los Angeles t Bureau of nngineering. The Laboratory is operated by the Drainage Systems Engineering Oivision headed by t.tr. Aaron I Aarons. It is under the general supervision of Mr. Walter L. T Couchman, Assistant Division nngineer. The staff of the Hydrauric Research Laboratory is under the direction of Mr. I ifames I. Nakao, Civil Engineer. The p"roject was under the direct supervision of Mr. Louie yamanishi, Civil Engineering t Associate. rl The research progiam was carried out primarily by Messrs. Richard weyermuLler, tqithael yamada, and sarvador I oregon. senior civil Engineering Assistants, who wele respon- sibre for fabrication of the model and the coLlection of the t data. Mr. John schumann, senior civil Engineering Assistant, I Mr. John Hoffman, civil Engineering Assistant and lvtessrs. Robert Borren and Gilbert L. Agaran, civil Engineering Drafting I Technicians, provided assistance in fabricating the modeL. Review and analysis of the test data and preparation of this t report hrere done by ltr. weyermuller. The graphicar presenta- I tions for this report were prepared by ptr. Agaran. The Laboratory staff wishes to aeknowledge the t assistance received from Mr. Walter Naydo, Civil Engineer, of l the Design Review Section, Bureau of nngineering. Mr. Naydo I l1 I I and con- t was in charge of the Laboratory during the design provide herpful struction of the moder and has continued to phase work' I suggestions during the experimental of the fol- I The Laboratoly staff also wishes to thank the lowing for their assistance t l.TheStructuralEngineeringDivisionofthe Bureau of Engineering for checking the structural I adequacy of the model- I 2. The Data Processing Group of the Bureau of Engi- neering for assistance in preparing the computer I programs used in analyzing the model' data' 3. The staff of the North District sewer Maihtenance I Division, Bureau of Sanitation, for the fabrica* tion of the steel hardware used in the model and I their assistance in erecting the model' I 4.TheAlhambraFoundryCorporation,Alhambra' grating Cali.fornia, for supplyirq one of the model I eonfigurations. 5.TheE.L.I.leBaronFoundrycompany'Brockton' I Massachusetts, for supplying one of the model I grat ing conf igurat ions. I I I I l.rL I t l TABLE OF COUPENTS Page I ABSTRACT..o............i 'l ACKNOV{LEDGMENTS.. o . o . ii LISTOFFIGURES......... ... vi t LISTOFTABLES............vi TIimRoDUcTION. o . ., . I I Background and Need for Investigation . 1 I Objectiveg. , . 4 TESTCONDTTIONS...... o. .... o.. 5 t Similitude. o . 5 ModeLRatios. : . o . o . 6 t ModeL Construction. 7 t Model operation . o . 8 DISCUSSION AND TEST RESUIJTS. 12 t Model Reliability at Shallow Depths . o . L2 Roughness Coefficients and Slopes r . 13 I GratesTested.o.. .. 13 t Methods of Presentation of Test Results . 15 Test Resultg. , . 16 I CONCIJUSIONSAND ADDITIONAT TESTING . 2l BTBIToGRAPI{Y.....o.. .. ... 24 t FTGURES AIID TABLBS . 25 I APPENDICES. ., . 40 I Notation. .. 4L t II Data Sumrnary. 43 I Lv TABLE OF CONTETITS Page APPENDICES(Cont'd) III Description of Grates Tested. aaoa 54 Iv Qualitative Test Result6. o aaaa 72 V Computel Programs . aaaa 79 I I t LIST OF FIGURES Page t FIGURE 1. Schematic of ModeL and Laboratory I Facilities... o , . 26 2. Photographs of the Model. o . 27 t 3. Cross Section of Model Roadbed and Support Stfuctufe . o . 28 t 4. Tlrpical Hal.f Street Section (above basin) . 29 5. Grating and Gutter. 29 I 6. $rpicalSurfaceWaves . .. 30 '1 l . Electric Point Gauge. 3L g. Depth of Flow vs. Street Flot,rr-. 32 I 9. Grates Tested Quantitatively. 34 10. Grate B Test Results. 35 ,l LL. Grate E Test Results. 35 t L2. Grate G Test Resu1ts. 36 13. GlateTTestResultE.. .... 36 I L4. Glate Cornparison at 4% Street Slope . 37 ls. I Grate Comparison at 16% Street SJ.ope. 38 LIST OF TABLES Page I TABLE 1. Model Ratios Based on the Froude Relation- I ship. aaaaaaaaaa 32 I 2. SLope and Roughness Relationship...... 33 3. Grate Capacity as a Percent of Street Flow. 39 t I vi t t I INTRODUCTION gackgrounAand l Need Fgr Investigatiqn The recent nation-wide increase in the use of natrow- I wheeled bicycles has caused concern for the safety of bicycle riders when riding over catch basin grates. This concern hag I caused many public agencies to review their policies regarding I catch basin grates. This report is the result of a reguest to the City EngLneer by the Council of the city of Los Angeles to t investigate the problem. The City nngineer in August, L973, directed the Hydraulic Research Laboratory to determine the t hydraulic capacities of bicycle-proof gratings for the City of T IJos Ange1es. Grate inlets have been found to be more economical I and effective than side opening inlets when used on streets with steep s!-opes. The need for an eeonomical catch basin for I steep slopes is especiaLly acute in toe Angeles where high in- t tensity winter storms oeeur in the heavily populated hiLlside areas of the City. I Bureau of nngineering records indicate that prior to 1926, bats for the standard grate inlet were placed perpendic- t ular to the curb. In L926 and 1927, the standard was changed, t and the bars were pLaced parallel to the curb to take advan- tage of greater hydraulic capacity. In addition, grates with I bars parallel to the curb showed less tendency to become clogged with debris. The use of grates of l-inch and ll-inch I T -1- I t (2.5 and 3.8 cm) spacing was contlnued until 1933. At this I time, the lk-inch spacing was eliminated because it was felt that the "balloon" bicycle tire of that day might sl.tp between I the bars, resulting in injury to the bicycle rider. I From 1933 untiL 1957, the Cityrs standard plan con- tained bars parallel to the curb with l-inch (2.5 crn) spacings. I In 1957, this spacing was narrowed to 3/4-Lnch (1.9 cm) because oftheincreaeedugeofnarro.w-tiredbicyc1essimi1artothose I popular today. Since the adoption of the 3/4-inch (1.9 cm) t bar spacings, City records show no official complaints due to bicycl-e tires slipping between thE bars of this grate. Hohtever, I concern has arieen ovet the possibility of rocks being forced between the bars by truck tj.ree. It is possible that the rocks I could spread the bars of a 3/4-inch (1.9 cn) grate enough to allow a bicycle tire to slip between the bars. Thie could I possibly prevent the 3/A-i,nch (1.9 cm) grating from being I bicycle-safe unl-ess a continuous program of inspection and repair is maintained, I In L972, the California LegisLature paesed, and the covornor signed into law, AssembLyBill No. 1L0L. The Bill I reguired that on eonetruction under contract advertised by t governmental bodies after July l, L973, grates which are not hazardous to bicycle riders must be specified. I In order to compJ.ywith the new law, the Buteau of Engineering, in lrtay of 1973, adopted aE a Etandard a'grating I similar to the Los Angeles County Flood Control District T -2- T I I I (r,acrcp) Frame and Grating (Bureau Standard PLan s-342-0). This grating was considered bicycle-safe'by the LACFCD(1)* t and was used as an interim standard until the completion of preliminary tests by the Bureau's ttydraulic Research Laboratory. I In,IuJ.y of 1973, the Bureaurs standard plan was rerrised to re- fLect the results of the first phase of the present testing I program.

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