The URL can be used to link to this page

Home My WebLink About6604; Romeria Street Drainage Improvements; Romeria Street Drainage Improvements; 2007-02-12LlVUll~ILcNI~U ~L!l~sr\ld 1 February 12,2007 KICK Ms. Sherri Howard City of Carlsbad '2075 Las Palmas Drive Carlsbad, California 92009 SUBJECT: HYDROLOGIC AND HYDMULIC ANALYSES FOR ROMERIA STREET DRAINAGE IMPROVEMENTS (RICK ENGINEERING COMPANY JOB NUMBER 15369) Dear Ms. Howard: Pursuant to our field meeting, this letter presents the results of the preliminary drainage analysis prepared for the existing concrete trapezoidal channel, and the RCP culvert under La Costa Avenue. The project site is located in the City of Carlsbad, and is bounded by La Costa Avenue on the northern side, Romeria Street on the eastern side, and Levante Street to south. This study analyzes the 400 feet of concrete channel upstream of the RCP culvert under La Costa Avenue. Refer to the Vicinity Map in Attachment A for the location of this project. Current Condition In the current condition, the concrete channel has been subject to undermining md has 'deteriorated since construction, please see the photos in Attachment B. Per the -improvement plans, the channel geometry consists of a l-foot bottom width, and 1.5:l @:v) side slopes. The channel discharges to an existing RCP storm drain under La Costa Avenue. The current channel alignment, and stom drain inlet location are located in Attachment C on the La Costa Vale Unit 1 ("DWG. 3036-1 Sht, 6 and DWG. L6392 Sht. 2,5,6) plan sheets provided. Per the plans, the existing culvert geometry is a 42-inch diameter RCP. However, field data indicates a 48-inch RCP exists in this lucation. For the hydrologic modeling, a 48-inch pipe was assumed. NOTE: The plan sheets provided in Attachment C are based on NVGD29 and the topography shown on the Current Condition Rational Method Worhap is based on NAVD88. Near this project, the elevation difference between NVGD29 and NAVDS 8 is approximately 2.22 feet. (i-e. NVGD29 Elev. = 100 fi. therefore NAVD88 Elev. = 102.22 ft -1 Hydrologic Methodology and Criteria Chapter 5 of the Drainage and Storm Drain Standards hated in the City of Carisbad Engineering Stambrds Vol. 1 (2004) states that the rational formula shall be used for watersheds less than 0.5 square miles. The area contributing runoff to the channel is a uniform deveIopment type consisting of single family residential houses, excluding the area immediately surrounding the channel and the graded slopes between lots. The entire watershed area was assumed Hydrologic 5620 Friars Road San Diego, California 92 11 a2596 (619) 2914707 FAX-: (61 91 281-4165 - rl&engineefing.cam 5AN DlECO RIVERSIDE ORANGE SACRAM EMTO PHOENIX TUCSON Mi. Sherri Howard February 12,2007 Page 2 of 4 Soil Type 'D" for these analyses. For the hydrologic model, the following C values were used. Table 1: Runoff Coefficient Summa Land-Use Percent C-Value Dmri tioa Im rvious Residential Undevelo ed 0.3 5 The Rational Method analysis for this project consists of analyzing the current condition in order to determine the peak ff ow-rate for a 100-year, 6-hour storm event. Rainfall depth was determined using the Counw of San Diego HydkoZogy Manual Rainfall ~oplzmiaIs. The 100-year, 6-hour storm event precipitation depth taken from the Isopluvial Chart is 2.7 inches. A copy of the Isopluvial chart is located in Attachment D. The watershed area contributing to the channel and the culvert entrance upstream of La Costa Avenue is approximately 75 acres. This includes the open space area dosely surrounding the channel, and the residential lots surrounding the project site. Storm runoff is routed into the channel through storm drains outletting into the channel. The current condition channel alignment, and storm drain outlet locations are located in Attachment C on the La Costa Vale Unit I plan sheets provided. The RCP culvert under La Costa Avenue continues north for approximately 850 feet, and outlets into San Marcos Creek. Between the entrance and outlet of this RCP culvert, inlets and other storm drains intersect the culvert increasing the flow rate within the culvert. The Rational Method analysis includes all tributary watershed areas, which contribute nmoff into the culvert. A summary of flow rates dong the culvert organized by node number is located in the Table 2 below in the @droIo@c Reds section. Hydrologic Results The Rational Method computer output for the lothyear, 6-hour storm event for the current condition is located in Attachment F in this letter. The time-of-concentration and the peak flow rate are computed at every node within the hydrologic model, which is shown on the Current Condition Rational Method Wurhp located in Attachment E. For this project, the focus is the peak flow through the trapezoidal channel to the RCP culvert ruaning under La Costa Avenue. For the detailed Rational Method analysis output report please see Attachment F. Table 2: Flow Rate Summary within La Costa Avenue Culvert I Nde I Flow rate (cfs) I Notes I Number 300 310 315 400 134 166 209 209 Culvert entrance south of La Costa Avenue Approx. 200 feet north of La Costa Avenue Id& at Gibrahar Street & Storm Drain Junction Culvert outlet Ms. Sherri Howard February 12,2007 Page 3 of 4 Preliminary Analysis and Results Two hydraulic calculations were prepared for this project. The first calculation was performed to determine if the original channel design is adequate to convey the peak flow rate through the channel based on the new County HydroIogy Manual. A typical cross- section illustrating the cb1 dimemions can be seen on the current condition plans located in this letter in Attachment C. Based on the plans the channel dimensions are as follows: Side Slopes 1.5: I (h:v) Bottom Width = 1 foot Depth = 2.6 feet The average slope based on current topography is approximately 6% to 7%, which corresponds with the 7% channel slope stated in the plans. A Manning's n-value of 0.014 was used for the open channel based on Table A-4 from the San Diego County Drainage Design Manual July 2005. Manning's equations for open-channels was used to determine normal depth for the peak flow yield4 by the Rational Method. For a 6% slope, the normal depth within the channel is 1.67 feet and for a 7% slope, the normal depth within the channel is approximately 1.61 feet Results hm the trapezoidal channel calcdations can be found in Attachment G of this letter. The sscond calculation was performed to determine the adequacy of the RCP culvert located under La Costa Avenue to intercept the 100-year flow. An inlet control calculation was performed using Chart 1B from the Sun Diego Couniy Drainage Design Manual. Based on the plans provided in Attachment C, the existing RCP culvert under La Costa Avenue measures 42 inches however based on field information, the culvert measures 48 inches. An inlet control calcuIation for both a 42 and a 48-inch pipe were performed, and the headwater required is approximately f 0.2 and 7.4 feet respectively. The inlet control calculation can be found in Attachment G of this letter. Inlet control was assumed to determine the potential for ponding water at the entrance of the RCP culvert entrance. To determine if inlet control governs, and determine the ponded water surface elevation in more detail, further hydraulic analysis for the entire culvert may be required during &d design. Conclusion Based on the peak flow rate resulting hm the Rational Method analysis, the cwrent design for the trapezoidal channel will be adequate to convey the 1 00-year, 6 hour storm event, when flowing at normal depth. However, with either a 42 or 48 inch RCP culvert, assuming inlet control, the headwater at the culvert entrance will pond approximately 10.2 to 7.4 feet above the culvert flowline, respectively. The ponded water surface elevation has been illustrated over an aerial photo located in Attachment H. Due to the potential ponding of water at the Ms. Sherri Howard February 1 2,2007 Page 4 of 4 culvert entrance, the riprap slope protection may require additional review to verify it is adequate to protect the culvert entrance hm erosion. Please see Attachment H, to view the approximate limits of the ponded water surface elevation overlain the recent aerial photo. A debris barrier is called out on DWG. L6392 Sht. 2 located in Attachment C, at the entrance of the RCP culvert. However, this could not be verified in the field. Recommendations for a debris barrier may require further consideration during final design. If you have any questions regarding this package or need any additional idormation about this project, please contact Roberta Cronquist or Edgar Camerino by telephone at (61 9) 29 1 -0707 Sincerely, RICK ENGINEERING COMPANY Lc&> Dennis C. Bo ing, M. Enclosures Attachment A Attachment B Attachment C Attachment D Attachment E Attachment F Attachment G Attachment H Vicinity Map Photographs of the Existing Trapezoidal Channel La Costa Vale Unit 1 Plans San Diego County Hydrology Manual Rainfall Isoplwials La Costa Avenue Current Condition Rational Method Workmap Current Condition Rational Method Analysis Hydrauiic Calculations Ponded Water Sdace Limits at La Costa Ave. cc: Mr. Edgar Camerino - Rick Engineering Company (with enclosures)