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Home My WebLink AboutCDP 02-28; KIKO RESIDENCE; WAVE ACTION STUDY; 2002-05-01I· I I I I I I I I I I I I I I I ,, I I Et:: SKELLY ENGINEERING WAVE RUNU-P & COASTAL HAZARD. STUDY 2649 OCEAN STREET CARLSBAD,CA MAY 2002 Prepared For Mr. Frederick Kiko 619 South Vulcan Avenue, Suite 214B Encinitas, CA 92024 Phon_e (~60)942-8379 Fax 942-3686 ( ,;.<filrii"1~~-:::=>,;a~ ~5< ,, ( \ ~ ~'"' \ \~ . ~'«~ . ' -..... ,, __ , ,~ -~ I I I I I I I I 'I I I ,, I I I I I I I WAVE ACTION STUDY 2649 Ocean Street, Carlsbad May 24, 2002 Mr. Frederick Kiko C/0 Wolf Design Build 1459 Lieta Street San Diego, CA 92110 PAGE1 SUBJECT: Wave Action & Coastal Hazard Study 2649 Ocean Street, Carlsbad. Dear Mr. Kiko: At your request, we are pleased to present the following letter report concerning wave action and the vulnerability to coastal hazards at the subject property. INTRODUCTION The subject site, located at 2649 Ocean Street, Carlsbad, California, lies on top of a wave cut sea cliff which backs a low sand and cobble beach. The lot is about 50 feet in width along the ocean parallel property line. The seaward portion of the property is protected from minor wave attack by "pickle weed" vegetation with a low height timber bulkhead beneath it (see Photographs 1 & 4). The properties to the south are protected by a series of seawalls (see Photograph 2). The properties to the north are protected by a continuous quarry stone revetment. The site have been subject to wave attack in the past, primarily during the 1982-83 El Nino (see Photograph 3). Photograph 1. Subject site as seen from the beach April 1, 2002. SKELLY ENGINEERING (760) 942-8379 I I I I I I I I I I I I I I I I I I I WAVE ACTION STUDY 2649 Ocean Street, Carlsbad Photograph 2. Adjacent seawall on properties to the south of the subject site. Photograph 3. Quarry stone revetment protecting properties to the north of the subject site. PAGE2 SKELLY ENGINEERING (760) 942-8379 I I I I I I I I I I I II I I I I I I I WAVE ACTION STUDY 2649 Ocean Street, Carlsbad PAGE3 The beach in front of the site currently consists of sand and cobbles that overly a formational sandstone. The beach in this area was nourished by the regional beach replenishment project last year. Much of that nourishment sand is still in the beach profile above low water. The nourishment sand thickness on the beach varies from 1 foot to over 5 feet. Just landward of the western property line the sand and cobble layer is about 4 ± feetthick. Below the cobble layer is the Santiago Formation, an Eocene bedrock material. This site, and neighboring Carlsbad beaches, are situated along a moderately high wave energy portion of the Southern California coast. This report constitutes an investigation of the wave and water level conditions expected at the site in consequence of extreme storm and wave action. It also provides conclusions and recommendations regarding the stability of the site and vulnerability to coastal hazards. Finally, this report provides preliminary designs, and design parameters for shore protection at the site. DATUM The datum used in this report is Mean Sea Level (MSL), which is +0.19 feet National Geodetic Vertical Datum (NGVD). In the open ocean off the San Diego County coast, Mean High Water (MHW) is 1.87 feet above MSL. The units of measurement in this report are feet (ft), pounds force (lbs), and second (sec). A survey performed by San Diego Land Surveying and Engineering, Inc on February 14, 2002 was provided by the designer, Mr. Wolfram Kalber. SITE INSPECTION A visual inspection of the site and the adjacent properties was performed on April 1, 2002. There currently exists an older residence on the site. It is our understanding that this structure is to be removed and a new single family residence constructed. The site sits atop a sea cliff. Photograph 4 taken in 1989 shows a timber bulkhead fronting the site. During the site inspection the location of the timber bulkhead was verified. Only the upper portion of the wall was exposed and it appears to be in good/fair condition. The wall sits on the western property line and provides protection of the slope from wave runup attack. The wall was most likely constructed after the 1982-83 El Nino winter. Photograph 4 shows the cobble field that currently lies beneath and within the recently nourished sand beach fronting the site. The area behind the bulkhead is planted with heavy ice plant or "pickle weed". This vegetation does provide some protection of the slope from wave overtopping of the timber bulkhead but does not protect the toe from extreme wave runup attack. In order to determine the vulnerability of the site to wave runup a wave runup an overtoppi'ng analysis is performed herein. SKELLY ENGINEERING (760) 942-8379 I I I I I I I I I _I I I I I I I I I I WAVE ACTION STUDY 2649 Ocean Street, Carlsbad PAGE5 75+ year recurrence storm. The onshore wind speed was chosen to be 40 knots. During storm conditions the sea surface rises along the shoreline (super-elevation) and allows waves to break closer to the shoreline and runup on the cobble beach. Superelevation of the sea surface can be accounted for by: wave set-up (1 to 2.5 feet), wind set-up and inverse barometer (0.5 to 1.5 feet), wave group effects ( 1 to 2.5 feet) and El Nino effects (0.5 to 1.0 feet). These conditions rarely occur simultaneously. The extreme water elevation used in this analysis is +6.0 MSL (100 year recurrence water level). The wave that has the greatest potential run up onto the site is the wave that breaks at the toe of the cobble and rides up the cobble slope to the site. This is due to the very large cobble field which is held in place by the northern jetty at Agua Hedionda. The El Nino waves in February 1982-83 did run up onto the properties and eroded some of the toe of the slope. It was in response to this extreme short term erosion that the small wooden run up walls were constructed. It is under these conditions that the maximum wave runup will occur. This is confirmed by an interview with the next door neighbor who has lived on the adjacent property for 40 years. Therefore, the runup analysis problem is for the beach to be at maximum scour, with a cobble slope leading up to the site. For the purpose of the run up analysis the small wooden walls are considered to not be there or failed. The design wave is not the largest wave to come into the area. The larger waves break offshore of the beach and lose most of their energy before reaching the shoreline. If the total water depth is 7 feet, based upon a maximum scour depth at the toe of the beach/cobble slope of-1. 0' MSL and a water elevation of +6. 0' MSL, then the design wave height would be about 6 feet. The effective height of the shore protection is +14' MSL. The cobble slope is 10/1 (horizontal/vertical) and the nearshore slope was chosen to be 1/60. Table I is the ACES output for these design conditions. Table I WAVE RUNUP AND OVERTOPPING ON IMPERMEABLE STRUCTURES Item Unit Value Wave Hei~ht at Toe Hi: ft 6.000 Wave Period . T: sec 20. ooo COTM of Nearshore Slope 60.000 Water Depth at Toe · ds: ft 7.000 COTAN of Structure Slope 10.000 Structure Height Above Toe hs: ft 15.000 Deepwater Wave Height HO: ft 3.231 Relative Height (ds/H0): 2.167 Wave Steepness {H0/gTA2): 0.251E-03 Wave Runup R: ft 11.107 Onshore Wind Velocity U: ft/sec 67.512 Overtopping Coefficient Alpha: 0.S0OE-01 Overtopping Coefficient Qstar0: 0.140 Overtopping Rate Q: ftA3/s-ft 0.262 SKELLY ENGINEERING Smooth Slope Runup and Overtopping (760) 942-8379 I I I I I I I I .I :I I I I I I I I I , I ., . ')! WAVE ACTION STUDY 2649 Ocean Street, Carlsbad PAGE6 CONCLUSIONS • • • • The site has been subject to wave attack from extreme wave runup in the past resulting in some erosion of the toe of the slope. Wave runup can reach as high as approximately +18' MSL on the natural slope. The properties to either side of the site have shore protection either in the form of a seawall or a quarry stone revetment. There exists a timber bulkhead on the property that provides minimal protection of the slope from wave runup. The wall has a shallow foundation well above the possible maximum scour elevation. The wall is. in disrepair, well into it useful life, and should be replaced with a properly designed shore protection structure. Even with the bulkhead in place, if the site is allowed to erode further as a result of extreme wave action the adjacent properties will be in jeopardy due to erosion out flanking the existing shore protection. RECOMMENDATIONS • Long term stability of the site and the adjacent properties will depend on the prevention of the occasional erosion of the slope by extreme wave attack. The existing bulkhead should be replaced with an engineered structure that meets the current design standard for shore protection. The shore protection proposed is a vertical seawall roughly in line with the seawall to the south. • The vertical seawall should be constructed of steel reinforced concrete. The seawall should be located at the western property line ( or just landward) and be founded into the formational material at about elevation +5' MSL. The top of the seawall should be about +18.0' MSL to minimize overtopping. CERTIFICATION This report is prepared in accordance with accepted standards of engineering practice, based on the site materials observed and historical data reported. No warranty is expressed or implied. SKELLY ENGINE~klNG (760) 942-8379 I I I I I I I I I I I I I I I I I I I WAVE ACTION STUDY 2649 Ocean Street, Carlsbad RE;FERENCES PAGE7 Inman, D.L. and S.A. Jenkins, 1983, "Oceanographic Report for Oceanside Beach Facilities", prepared for the City of Oceanside, California, 206 pp. USACOE 1984 Shore Protection Manual. USACOE 1988 CCSTWS report #88-6 "Historic Wave and Water Level Data Report San Diego Region. If you have any question regarding this letter report please contact us at the number below. Respectfully Submitted, __ ,'//.~ David W. Skelly MS, PE RCE#47857 Coastal Engineer SKELLY ENGINEERING (760) 942-8379