BALLONA CREEK 4 LEVEE SYSTEM LOS ANGELES COUNTY, CALIFORNIA NLD SYSTEM ID #

Transcription

1 LOS ANGELES COUNTY, CALIFORNIA NLD SYSTEM ID # PERIODIC INSPECTION REPORT NO 1 GENERALIZED EXECUTIVE SUMMARY FINAL SYSTEM RATING: MINIMALLY ACCEPTABLE FINAL RATING DATE: 9 DEC 2014 PERIODIC INSPECTION REPORT PREPARED BY THE U.S. ARMY CORPS OF ENGINEERS, SAN FRANCISCO DISTRICT SUBMITTED: NOVEMBER 2013 INSPECTED: MARCH 19-21, 2013

2 EXECUTIVE SUMMARY This Executive Summary provides an introduction to the Ballona Creek 4 (BC4) Levee System Periodic Inspection Report No. 1, an overview o the system, a summary o the major indings o the periodic inspection, and the overall rating or the system. 1.1 Scope and Purpose o Periodic Inspections The purpose o this levee system periodic inspection is to identiy deiciencies that pose hazards to human lie or property. The inspection is intended to identiy the issues in order to acilitate uture studies and associated repairs, as appropriate. This assessment o the general condition o the levee system is based on available data and visual inspections. Detailed investigation and analysis involving hydrologic design, topographic mapping, subsurace investigations, testing, and detailed computational evaluations is beyond the scope o this levee system inspection. 1.2 System Summary The BC4 Levee System is located in the City o Los Angeles in Los Angeles County, Caliornia. The levee length, as scoped, consisted o Segment 4a, maintained by the Los Angeles County Department o Public Works (LACDPW), and Segment 4b, maintained by the Corps o Engineers. During the inspection, it was ound that all o Segment 4b and part o Segment 4a were channels with no levee prism. The total length o the system is approximately 2.63 miles, not including the channel reaches. The BC4 Levee System runs along the let bank o Ballona Creek between the Centinela Creek conluence at Station to Overland Avenue at approximately Station Figure 1 shows the extent o the levee system. Note that a levee does not exist along the reach upstream o the Overland Avenue, thereore, the upper reach o the original BC4a Segment and the BC4b Segment have been removed rom the BC4 Levee System, and are thus not discussed in the main body o the periodic inspection report. The BC4 Levee System downstream o Centinela Avenue bridge at Station consists o a sot or earthen bottom trapezoidal channel with stone revetment on the lower part o the bank, and reinorced concrete revetment on the upper part o the bank where the levee had been raised. The bottom o the channel upstream o the Centinela Avenue bridge crossing is concrete. The BC4 Levee System transitions rom a trapezoidal channel to a concrete U-wall channel with side slopes at the top o each bank between Station and It is a rectangular channel upstream rom Station According to the as-built drawings, the BC4 Levee System consists o 5 side drainage structures and 8 bridge crossings. The BC4 Levee System, along with other similar works in the Los Angeles County Drainage Area (LACDA), was authorized initially by the Emergency Relie Act o 1935 to provide drainage and lood control. On 30 June 1937 it was transerred to the more comprehensive project adopted in the Flood Control Act o 22 June The Flood Control Acts approved 22 June 1936 and 15 May 1937, authorized the construction o reservoirs and channel improvements on the Los Angeles and San Gabriel rivers and Ballona Creek, and tributaries thereo. The Flood Control Act approved 18 August 1941, approved the general comprehensive plan or lood control and other purposes in the basins o these streams. Page 2 o 5

3 1.3 Summary o Major Deiciencies Found and Subsequent Repairs The levee system was inspected on 19 through 21 March During the periodic inspection o the system, several deiciencies were noted or which remedial actions are required. The corroded corrugated metal pipe (CMP) at Station just downstream o the Sawtelle Boulevard bridge was critically unacceptable. The Los Angeles County Department o Public Works (LACDPW) has since made repairs to: the 18-inch diameter CMP at Station and the caved-in stone revetment just downhill o the pipe; the 30-inch diameter CMP at Station ; and the 24-inch diameter CMP at Station These deiciencies and repairs are urther discussed under item 9, Interior Drainage System checklist in Appendix III o the Periodic Inspection Report. Photos and s documented completion o the repairs, and were provided by 11 September Other major deiciencies that were noted during the periodic inspection o the project eatures are: non-compliant vegetation growth; encroachments that prevent proper inspection o the landside slope (e.g. ence) and/or negatively impact the integrity o the levee (e.g. culverts); unknown condition o the culvert penetrations (i.e. internal inspection has not been perormed); elevations or the levee system have not been re-evaluated based on guidance provided in ER The levee crest elevations could not be directly compared to the as-built elevations to assess settlement and capacity (with respect to top o system elevation); depression observed in the stone revetment near the downstream end o the levee system; crack longitudinal to the levee was observed approximately ¼ way up rom the toe o the bank. The crack propagated through both wing walls o the drainage structure at approximately Station and had a vertical oset o ¾ at Station ; and spalling and cracking was observed in the reinorced concrete revetment on the waterside levee slope. 1.4 Overall Rating The Levee Saety Out-Brie Meeting was held 23 July The BC4 Levee System is tentatively rated Minimally Acceptable until urther review rom USACE Los Angeles District (herein reerred to as USACE). A Minimally Acceptable system rating is deined as: One or more items are rated as Minimally Acceptable or one or more items are rated as Unacceptable and an engineering determination concludes that the Unacceptable items would not prevent the segment/ system rom perorming as intended during the next signiicant runo event. The local sponsors will be notiied o the overall rating o the levee system by letter with instructions to correct the Unacceptable rated items as soon as possible, not to exceed two years, Page 3 o 5

4 and to correct the Minimally Acceptable rated items so that they do not deteriorate urther and become Unacceptable. Page 4 o 5

5 u ;_... 0 I t. ~ n ~! c...,...,w.. i....,.,, e w--! !I. ~. :1 ~..,.,.... g.. or~ (II. ; ~ \..,.,...,, Playa Vista ~-. i """.-oo I. i r CwllllPl... Alsace!!.,~br ~-~.., Blanco-Culver Crest, I. I - channel - Levee Leveed A rea EJ:I Proposed Leveed Area Blair Hills I~ 0 \, ,200 ~-----""======:::I Feet Basemap Source: ESRI. World Imagery. Last updated June Accessed on maps/world_lmagery. \., Figure 1: Ballona Creek 4 Levee System Page 5 o 5 "llr.. ~... 1,... 4 ~hu;~~d;;n, ~lon;;;~avte~~ USGS. ~ptermap. PC, NRCAN, Esri,dapan. METI, Esn Ch1na (Ho..ng Kong), Esn, om om, ~!>...,..,.. ~ ~\. ~ ~ g i LOCATION AND LEVEED AREA MAP r ~ U.S. ARMY CORPS OF ENGINEERS LOS ANGELES DISTRICT