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HomeMy WebLinkAbout; Appendices E-G - FEMA Review; Storm Water; 1990-05-01MA!SlXR PLAN OF DRAINAGE FOR THEClTYOFCARCSBAD FEMAREVIEW L BUENA VISTA CREEK CITY OF CARLSBAD DEVELOP. PROC. SERV. DiV. FRASER ENGINEERING, INC. COOPER ENGINEERING ASSOCIATES - A JOINTVENTURE CITY OF CARLSBAD MASTER PLAN OF DRAINAGE FEMA REVIEW BUENA VISTA CREEK May 1990 .- CITY OF CARLSBAD MASTER PLAN OF DRAINAGE FEMA REVIEW BUENA VISTA CREEK INTRODUCTION The review of the existing FEMA flood plain maps in this report has been done as part of the 1988 Storm Drain Master Plan for the City of Carlsbad, San Diego County, California. One of the important features of the plan is to accurately identify the 100 year flood plain and floodway of Buena Vista Creek within the city. The updated plan is intended to serve as a blueprint for future drainage improvements, including cast assessments, within the city and to provide guidance to future land development. In this review the flood plain boundaries and water surface elevations, if present, on the maps published by FEMA were studied and compared to the data available in existing studies. The topographic maps on which the existing studies are based have also been compared to the 1988 topographic maps prepared as a part of the 1988 Storm Drain Master Plan for the City of Carlsbad. A summary of the findings and recommendations has been prepared. Photographs of drainage structures and the type of vegetation in the channel are included in the report. The map on Plate 1 is on index map showing the location of each photograph. WCATION AND DRAI NAGE The review in this report covers the reach of Buena Vista Creek within the City of Carlsbad corporate limits. The area of study is shown on the location map in plate 1. - The Buena Vista Creek watershed is located in the northwest portion of San Diego County, about 33 miles north of the city of San Diego along State Highway 78. The creek drains an area of approximately 19 square miles. The drainage area is long and narrow with a distance of about 9 miles from the Pacific Ocean to its highest peak and a width of about 2 miles. It is bounded on the north by the San Luis Rey River basin: on the south by the Agua Hedionda Creek basin: on the east by San Marcos Mountains: and on the west by the Pacific Ocean. Buena Vista Creek originates in the San Marcos Mountains and flows westerly along the northern city boundary, just south of Highway 78, into Buena Vista Lagoon which empties into the Pacific Ocean. Interstate Highway 5 crosses Buena Vista Lagoon just east of the outflow to the ocean. - Flow is generally westward within Carlsbad and eventually enters the Pacific Ocean after being temporarily delayed by the considerable storage in the lagoon. The stream gradients of the reach within Carlsbad City limits average 32 feet per mile. The reach of Buena Vista Creek under this review is 4.4 miles. The creek has a natural channel of narrow width and wide overbanks before entering an improved channel about half a mile upstream of El Camino Real. State Highway 78 abuts the creek on the north side - for the entire study reach east of Interstate Highway 5. Most of the land adjacent to the creek has been developed west of El Camino Real. There is minimal development along the creek east of El Camino Real. The provision of excellent transportation facilities, however, will definitely contribute to increased residential, commercial and industrial development in the area. Natural vegetation is abundant on the floodplains. It consists mostly of native grasses, brush and trees. A short reach of the floodplain about half a mile upstream from El Camino Real is covered with dense growth of vegetation and large trees. EXISTING STUDIES - 1. One of the more comprehensive studies for Buena Vista Creek is the Flood Plain Information for Buena Vista Creek, Pacific Ocean to Vista, by the Los Angeles Corps of Engineers dated July 1973. The reach of the creek studied in the report starts at the mouth of the lagoon at the downstream end and stretches upstream to .2 miles northeast of the Highway 78 crossing. The study includes drainage areas and peak flows along different reaches of the creek, specific information on culverts and bridges across Buena Vista Creek and channel and overbank velocities. Also included in the report are 1"= 600' scale maps of the flood plain. These maps were used for the delineation of the 100 year flood plain and the 100 year flood profiles. The maps used for the delineation of the 100 year flood plain in the report are based on 1960 and 1972 topography. 2. In December of 1976 the Department of Sanitation and Flood control, San Diego County, published a Hydrology Report for Buena Vista Creek. This report was later revised in November 1977. San Diego County's Hydrology report lists 100 year peak flows in a more detailed break down along the creek. The study lists the 10 year, 50 year, 100 year and 500 year discharges at several concentration points within the creek's drainage basin. Also included are tables comparing the 100 year flood flow rates to the equivalent data in the 1973 corps of Engineers study mentioned above. The flood flow rates developed in the San Diego County report are within 13% of the Corps of Engineers flow rates. The Corps of Engineers flow rates were revised based on the County's areas in May 1976. 3. A Special Flood Plain Delineation Study was completed for Buena Vista Creek by Nolte and Associates in February 1978. The study was based on December 1974 topography. The flow rates used for this study are those of the Hydrology Report by San Diego County Flood control Department mentioned above. This study is a complete hydraulic analysis of the flood plain and covers the portion of the creek from El Camino Real at the downstream end to State Highway 78 at the upstream end. 100 year flood boundaries and profiles were determined using a HEC-I1 computer model as part of this study. 4. As a extension to the 1978 Flood Delineation Study, Nolte and Associates prepared a hydraulic analysis for Buena Vista Creek downstream of El Camino Real in June 1986. 100 year flood boundaries and profile were determined in this study based on the 1975 topography, using a HEC-I1 computer model. This study covered the reach of the creek from Interstate Highway 5 to El Camino Real. FINDINGS AND RECOMMENDATIONS Areas of 100 year flood and base flood elevations have been determined and shown on FEMA's September 1987 revision of 1'= 500' scale Flood Insurance Rate Map. The flood plain data on FEMA's map is based on Noltels 1978 and 1986 studies. In this review approximate flood plain width and elevations on FEMA maps were compared to the equivalent data in the Los Angeles Corps of Engineers Flood Plain Information Study. The 100 year flow rates used in the HEC-I1 analyses of 1978 and 1986 were compared with the flow rates listed in the San Diego County's 1976 Hydrology Report. Input parameters to the HEC-I1 computer model such as roughness coefficients and bridges were checked against existing conditions. Finally, the base topographic maps used for the 1978 and 1986 studies were compared with the 1988 topography. - Following is the summary of the findings: 1. 100-YEAR FLOOD FLOW RATES - The discharges used in both the 1978 and 1986 Flood Plain Delineation Studies by Nolte generally match the flow rates established by the San Diego County's 1976 Hydrology Report. 2. FLOOD PLAIN BOUNDARIES - The 100 year flood plain delineated on FEMA's 1987 revision of the Flood Insurance Rate Map for Buena Vista Creek has been adopted from the 1978 and 1986 Flood Plain Delineation Studies by Nolte. 3. ROUGHNESS COEFFICIENTS - Value of 0.03 is an underestimate for the channel's roughness between sections 27.2 and 30.0 of Noltels 1986 HEC-I1 computer model. Approximately 30% higher values should have been used. See picture 8. Coefficients of 0.03 seems to be too high for the lined channel between sections 30.0 and 36.0 of Nolte's 1986 HEC-I1 computer model. A value of 30% lower should be used. See picture 9 through 11. 4. BRIDGES - The Interstate Highway 5 bridge has not been modeled in Nolte's 1986 study. See picture 4. The piers for Jefferson Street bridge have not been modeled in Noltels 1986 study. See picture 5. The private bridge of section 3.625, downstream of College Boulevard, has not been modeled in the 1978 study. See picture 13. TOPOGRAPHY - The northerly overbank of the creek channel east of Jefferson Street has experienced significant grading. The two open channels draining into the creek visible on the 1975 topography are no longer in existence. New structures have been constructed since 1975 on the channel's south overbank, north of Marron Road, west of Monroe Street. 5. The parking lot existing on the 1975 topography has been expanded along the channel's southerly overbank, north of Marron Road east of Monroe Street. CONCLUSIONS Based on the findings and analysis in this review a revision to the existing 100 year flood plain boundaries and elevations is recommended. The revision should include the incorporation of the data corresponding to the roughness coefficients based on the most recent vegetation growth in the channel, bridge characteristics and the most recent topographical features along the channel. The HEC-I1 study used by Nolte and Associates in June 1986 were based on 1975 topography. The topography completed in 1988 by the City of Carlsbad shows significant differences in culture, grading and channel features along the channel reach. This includes deposition and erosion in the channel causing changes in channel configuration. Thus, the cross-section input would cause significant differences in the HEC-I1 output results. This alone emphasizes why a new study is necessary. - It is also apparent that Buena Vista Creek is subject to Erosion/Sedimentation similar to many rivers and streams in San Diego County. As FEMA is now considering the effects of Erosion/Sedimentation along other streams in San Diego County we believe that Buena Vista Creek falls in this category. We would now urge FEMA to include this factor in the next flood plain delineation in order to see the effect of the Erosion/Sedimentation process. This information could be used to define a Erosion/Sedimentation hazard area. This area must cover potential changes in width obtained in mathematical modeling, and potential migration based upon geomorphic analysis, historical information, physical constraints, and man-made changes. Due to the heterogeneities in nature which affect any mathematical effort, a certain safety factor should be selected based on judgement and employed in arriving at a floodplain/erosion/sedimentation hazard area. Significant differences have been found in the roughness coefficients used in Nolte's 1986 HEC-11. This is most apparent when considering the roughness coefficients used at the location of Pictures 8 and 9. The observed values are at 30% variance with those used in the FEMA study. These are significant differences which would result in significant variances in the flood plain, thus requiring a new study. In addition to the above revisions, we believe that the bridges at Highway 5, Jefferson Street and College Boulevard should be modelled in a new study in order to arrive at an accurate flood plain. These bridges were not modelled in the previous st..dy. In summary, based on the above factors, a revision to the existing 100 year flood plain boundaries and elevations is now necessary. Picture 1 - Downstream view of the lagoon from the railroad bridge. Picture 2 - Downstream view of the railroad bridge. Picture 3 - Upstream view of Hill Street bridge. _- Picture 4 - Downstream view of Hwy 5 bridge. Picture 5 -.Downstream view of Jefferson Street bridge. _- Picture 6 - Downstream view of the channel from South Vista Way bridge. Picture 7 - Downstream view of South Vista Way bridge. Picture 8 - Upstream view of El Camino Real bridge. Picture 9 - Upstream view of the channel from El Camino Real bridge. _- Picture 10 - Downstream view of the channel from Haymar Street bridge. Picture 11 - Upstream view of Haymar Street bridge. Picture 12 - Downstream view of the channel from the private bridge. Picture 13 - Upstream view of the private bridge. w-'" - MASTER PLAN OF DRAINAGE FOR THEcrrYOFCARLSBAD .- AGUAHEDIONDA CREEK CITY OF CARLSBAD ~~V FRASER ENGWERING, INC. COOPER ENGINEERING ASS0CJA"ES A JOINT VENTURE - CITY OF CARLSBAD MASTER PLAN OF DRAINAGE FEMA FtEVIEW AGUA HEDIONDA CREEK May 1990 AGUA HEDIONDA CREEK INTRODUCTION The review of the existing FEMA flood plain maps in this report has been done as part of the 1988 Storm Drain Master Plan for the City of Carlsbad, San Diego County, California. In this review the flood plain boundaries and water surface elevations, if present, on the maps published by FEMA were studied and compared to the data available in existing studies. The topographic maps on which the existing studies are based have also been compared to the 1988 topographic maps prepared as a part of the 1988 Storm Drain Master Plan for the City of Carlsbad. A summary of the findings and recommendations has been prepared. The review in this report covers the reach of Agua Hedionda Creek within the City of Carlsbad corporate limits. The area of study is shown on the location map in plate 1. Agua Hedionda Creek originates in the hills south of the San Marcos Mountains and slows south westerly towards the Pacific Ocean. The creek flows through Los Monos Canyon at the city's eastern boundary. Los Monos Canyon has extremely steep gradients. The flow is contained inside a narrow channel for the entire distance of more than a mile through Los Monos Canyon. Downstream from Los Monos Canyon, Agua Hedionda Creek broadens out into a shallow, wider channel. The only major development along the channel is that of Rancho Carlsbad Mobile Park and Golf Course. The channel in Rancho Carlsbad Mobile Park and Golf Course is covered with natural grasses and occasional small trees on the banks. See pictures 10 through 12. Downstream of Rancho Carlsbad Mobile Home Park, from El Camino Real to Agua Hedionda Lagoon, channel and overbanks are covered with natural grass, brush and occasional trees. Downstream from El Camino Real the natural channel becomes shallow, with a very broad flood plain. See pictures 6 through 8. During large floods, flows exceed the channel capacity and inundate the flood plain before entering the lagoon. -~ The length of the reach of Agua Hedionda Creek under this study is 3.8 miles from the ocean upstream to Rancho Carlsbad Golf Course and 2.5 miles from Rancho Carlsbad to the city's corporate limits. EXISTING STUDIES In July of 1973 the Los Angeles Corps of Engineers published the Flood Plain Information for Agua Hedionda Creek, Pacific Ocean to Buena. The report lists 100 year peak flows at different points along the creek. Included in the report are 118= 600' scale maps of the 100 year flood plain and the 100 year flood profile. The San Diego County Department of Sanitation and Flood Control published a Hydrology report for Hedionda Creek in December 1976. - This report lists 100 year flows in a more detailed breakdown along the creek. The flood flow rates developed in the San Diego County report are slightly different from those of the 1973 Los Angeles Corps of Engineers report. Combining the data from both studies a table of peak flows has been prepared to be used in the flood plain mapping of Agua Hedionda Creek. These 100 year frequency peak flows are within 10% of both the flows computed in the County's anaylsis and those listed in the Corps of Engineers report. In February 1978, Nolte and Associates prepared a report for a special Flood Plain Delineation Study of Agua Hedionda Creek. The study was based on December 1974 topography. The flow rates used for this study are results of the 1976 study by the San Diego County Department of Sanitation and Flood Control. This study is a hydraulic analysis of the flood plain and covers the portion of the creek from Agua Hedionda Lagoon at the downstream end to Rancho Carlsbad Drive (East) at the upstream end. 100 year flood boundaries and profiles were determined, using a HEC-I1 computer model, as part of the study. The stream reach upstream of the Rancho Carlsbad Mobile Park was excluded from the study because it was determined to be too steep and undevelopable. FEMA's 1983 Flood Insurance Rate Map shows the portion of Agua Hedionda Creek within the Rancho Carlsbad Mobile Park and the portion upstream from Oak Lake. Areas of 100 year flood and base flood elevations have not been determined for the reaches shown on the map. The map merely presents the approximate location and width of the flood plain on a I"= 1000' scale. The 1984 Flood Insurance Rate Map shows the approximate location and width of the flood plain for the portion of the creek between Aqua Hedionda Lagoon and Rancho Carlsbad Mobile Park and the portion between Rancho Carlsbad Mobile Park and Oak Lake. Basically no base flood elevations have been determined for Aqua Hedionda Creek By FEMA. In this review approximate flood plain widths and locations on FEMA maps have been compared to the equivalent data in the 1973 Los Angeles Corps of Engineers Flood Plain Information report and the Nolte's 1978 Flood Plain Delineation Study. Also, the adequacy of the HEC-I1 computer modeled used by Nolte in terms of the 100 year flow rates, roughness coefficients and bridges has been reviewed. Finally, the base topographic maps used for the 1973 and 1978 studies were compared with the 1988 topography. - FINDINGS AND RECOMMENDATIONS 1. FLOOD PLAIN WIDTHS - FEMA's June 1984 Flood Insurance Rate Map delineates a generally wider flood plain for the creek, upstream from the lagoon to El Camino Real, as compared to the flood plain determined in the 1978 Nolte study. On FEMAIs map Calaveras (Hidden Valley) Road is inside the flood plain all along the creek and approximately 500' as it turns south easterly away from the creek. The portion of the flood plain in the left overbank just downstream of El Camino Real, shown on Nolte's 1978 work maps, is not reflected on the 1984 FEMA plan. Upstream of Rancho Carlsbad Drive (East) the flood plain extends all the way to El Camino Real, in the left overbank, as shown on plans in Corps of Engineers 1973 and Nolte's 1978 studies. Width of the flood plain is approximately 2000' according to the Corps of Engineers study. The flood plain measured to be about 400' wide on the FEMA map. 2. FLOOD FLOW RATES - The 100 year flow data used for input to the HEC-I1 computer model is the direct result of the San Diego County's Hydrology study in 1976, although the County's report recommends the usage of a modified table which lists approximate averages between the results from the County's study and the 1973 Corps of Engineers study.The flow rate used in the HEC-I1 model for Agua Hedionda Creek downstream of confluence with Calavera tributary is 9300 CFS while the County's study specifies a rate of 10000 CFS to be used for flood plain mapping. - Different flood flow rates used in the Nolte's 1978 study and Corps of Engineers 1973 study have contributed to the significant differences in the computed water surface elevations. - 3. ROUGHNESS COEFFICIENTS - The 1978 HEC-I1 computer model used c values of 0.025 for the channel and 0.03 for the overbanks inside the Rancho Carlsbad Mobile Park. Coefficients of 20% higher values would be more appropriate. See pictures 10 through 13. 4. BRIDGES - The bridge on Rancho Carlsbad Drive - East has not been modeled in the 1978 HEC-I1 computer model. See picture 12. 5. of Carlsbad Blvd. bridge has experienced new grading. TOPOGRAPHY - The northerly overbank of the creek channel east CONCLUSIONS: Based on the finding and analysis in this review a revision to the existing 100 year floor plain boundaries and elevations is recommended. The revision should include the incorporation of the data corresponding to the roughness coefficients based on the most recent vegetation growth in the channel, bridge characteristics and the most recent topographical features along the channel. - The latest FEMA flood plain maps in 1984 are based on 1974 topography. The topography completed in 1988 by the City of Carlsbad shows major differences in grading and culture along portions of the channel reach. Considering grading that has taken place in the channel overbank discussed herein and other topographic variation a review of this stream by FEMA is now warranted. Significant differences have been found between the roughness coefficients used in the 1978 HEC-I1 computer model and what is evident along the channel today. The observed values are 20% - higher than those used in the 1978 study which forms a basis for the 1984 FEMA study. - Considering the above factors and the need to model the bridge on Rancho Carlsbad Drive a revision to the existing 100 year flood plain boundaries and elevations is now necessary. i Picture 1 - Upstream view of the Carlsbad Blvd. S'ly bridge. I Picture 2 - Downstream view of the Carlsbad Blvd. N'ly bridge Picture 3 - Upstream view of the railroad bridge. Picture 4 - Upstream view of Hwy 5 bridge Picture 5 - View of the floodplain from the right overbank at mouth of the lagoon. Picture 6 - View of the floodplain from the right overbank upstream of the lagoon. Picture 7 - View of the floodplain from the left overbank downstream of El Camino Real. Picture 8 - Downstream view of the channel from El Camino Real bridge. Picture 9 - Upstream view of El Camino Real bridge. Picture 10 - Downstream view of the channel from Mata Road. Picture 11 - Downs.tream view of Rancho Carlsbad Drive (west) bridge. ?-- Picture 12 - Upstream view of Rancho Carlsbad Drive (east) bridge. _- Picture 13 - Upstream view of the channel from Rancho Carlsbad Drive (east) bridge. MASIER PLAN OF DRAINAGE FOR .- SAN MARCOS CREEK FRASER ENGINEERING, INC. COOPER ENGINEERING ASSOCIATES A JOINT VENTURE CITY OF CARLSBAD MASTER PLAN OF DRAINAGE FEMA REVIEW SAN MARCOS CREEK May 1990 SAN MARCOS CREEK INTRODUCTION The review of the existing FEMA flood plain maps in this report has been done as part of the 1988 Storm Drain Master Plan for the City of Carlsbad, San Diego County, California. In this review the flood plain boundaries and water surface elevations, if present, on the maps published by FEMA were studied and compared to the data available in existing studies. The topographic maps on which the existing studies are based have also been compared to the 1988 topographic maps prepared as a part of the 1988 Storm Drain Master Plan for the City of Carlsbad. A summary of the findings and recommendations has been prepared. - The review in this report covers the reach of San Marcos Creek within the City of Carlsbad corporate limits. The area of study is shown on the location map in plate 1. San Marcos Creek drains an area north of the San Dieguito River basin, originating in the mountains north and east of the city of San Marcos, and empties into the Batiquitos lagoon about 2.6 miles east of the Pacific Ocean. The creek flows in a general south- westerly direction. San Marcos Creek enters the city at the eastern boundary through the Rancho Santa Fe bridge. The flow is contained in a narrow, twisting, steep-sided canyon until the canyon suddenly ends east - of the Rancho La Costa development. See pictures 11 and 12. Through Rancho La Costa to the Batiquitos Lagoon the channel becomes small and not well defined, resulting into a broad flood plain. During large floods, flows exceed the channel capacity and inundate parts of the broad flood plain. See picture 9. San Marcos Creek enters Batiquitos Lagoon through the El Camino Real bridge. The lagoon provides considerable storage during large floods and ultimately empties into the Pacific Ocean through the Interstate Highway 5, AT&SF railroad and Carlsbad Boulevard bridges. The reach of the creek under this review is 2.6 miles long from the ocean to the upstream end of Batiquitos Lagoon and 3.7 miles long from the lagoon to Rancho Santa Fe Road at the city boundary. Natural vegetation in the reach consists mostly of native grasses, brush and some trees. There has been a great amount of urban development occurring in the area with additional areas planned for residential and industrial development. East of El Camino Real the Rancho La Costa Golf and Country Club occupy the entire flood plain. Urban development west of El Camino Real is located within close proximity to the ocean. - EXISTING STUDIES 1. In April, 1971 the U.S. Army Corps of Engineers, Los Angeles District, California prepared the Flood Plain Information for San Marcos Creek, San Diego County, California. The study covers the entire length of the creek within the City of Carlsbad. It also covers Encinitas Creek, a tributary of San Marcos Creek, which joins San Marcos Creek just before it enters Batiquitos Lagoon west of El Camino Real. The Corps of Engineers report is a comprehensive study on the San Marcos Creek flood plain. The report includes drainage areas and peak flows along different reaches of the creek, specific information on culverts and bridges across San Marcos Creek, and channel and overbank velocities. Also included in the report are 1" = 400' scale maps of the 100 year flood plain and the 100 year flood profiles. The maps used for the delineation of the 100 year flood plain in the study are based on 1961 topography. 2. The Los Angeles Corps of Engineers completed, in March 1975, a HEC-I1 computer model for San Marcos Creek which was used as the basis for FEMA's Flood Insurance Rate Maps for San Marcos Creek within the City of San Marcos. A copy of the printout of the computer run was located at the U.S. Army Corps of Engineers, Los Angeles District, Department of Flood Control. As it was determined by the Los Angeles Corps of Engineers Department of Flood Control the review of the existing HEC-I1 model would not be possible since the work maps showing the cross-sections taken for input to the computer program could not be located. 3. The comprehensive Plan for Flood Control and Drainage, Zone 1, San Diego County Flood Control District was completed by Koebig, Incorporated in July 1976. The study is a guide for development of a least-cost flood control and drainage systems for Zone 1 of the San Diego County Flood Control District. The study uses the data from the April 1971 Corps of Engineers study and the April 1973 Master Plan of Drainage Study for the City of San Marcos, By VTN. The Koebig study lists a summary of existing conditions, at the time, for the San Marcos Basin which includes Lower San Marcos Creek, i.e. the reach of the creek within the City of Carlsbad. Also included in the provided tables is the summary of the recommended improvements, if any, for each of the existing drainage lines. However, there is no analysis of flood plain or flood profile in the Koebig report. 4. A number of hydrologic and hydraulic studies have been conducted for the design of specific projects for San Marcos Creek in the vicinity of the City of San Marcos. Two major studies are the July 1988 Hydrology Report by Boyle Engineering and the August 1988 Flood Control Improvement Project Concept Report by Willdan Associates. - FEMA's 1" = 2000' scale Flood Insurance Rate Map, dated June 1984, has delineated approximate boundaries for the 100 year flood plain for Batiquitos Lagoon: and the 1' = 1000' scale Flood Insurance Rate Map, 100 year flood plain for San Marcos Creek from El Camino Real at the downstream end to Rancho Santa Fe Road at the upstream end. No areas of 100 year flood or base flood elevations have been determined in detail for San Marcos within the City of Carlsbad. Based on contacts with FEMA headquarters in Washington and FEMA's archives in Virginia and Maryland the delineation of flood boundaries for San Marcos Creek in Carlsbad ha5 been through approximate methods which no back up data is available. In this review the approximate 100 year flood boundaries on the FEMA maps were compared to the equivalent data in the 1971 Los Angeles Corps of Engineers study. Also the topographic conditions at the time of the 1971 and 1975 Corps of Engineers studies were compared with the 1988 topography. FINDINGS AND RECOEIMENDATI ON8 1. 100 YEAR FLOOD BOUNDARIES - The 1971 Corps of Engineers study delineates a generally wider flood plain than FEMA's maps. Some examples are as follows: Width of the flood plain as shown on FEMA's June 1984 Flood Insurance Rate Map measures to be approximately 300' wide between the Carlsbad Boulevard northbound and southbound lanes. The same cross-section on the 1971 Corps of Engineers flood plain measures to be 1500' wide. La Costa Avenue just east of Interstate Highway 5 is outside the flood plain on FEMA's 1987 Flood Insurance Rate map. The Corps of Engineers 1971 study shows approximately 1200' of La Costa Avenue as being inside the 100 year flood plain. Flood plain width just upstream of El Camino Real is approximately 800' on FEMA's 1984 map. On Corps of Engineers 1971 map the flood r - I ,-- plain is close to 1300' wide. 1. TOPOGRAPHY - The east side of El Camino Real has experienced significant residential and industrial development. The Rancho La Costa and Country Club have added a great deal of grading to the northerly overbank of the San Marcos Creek area. New structures on the southern overbank of San Marcos Creek, east of El Camino Real. Based on the new topographic maps completed in 1989, numerous changes in topography are evident compared to the previous topographic maps. CONCLUBIONS According to the finding and analysis in this review a revision to the existing 100 year flood plain boundaries and elevation is recommended. The revision should include all of the new structures in the area and the most recent topographical features along the channel. L Picture 1 - Downstream view of the lagoon at entrance to the ocean. Picture 2 - Upstream view of the south bound Carlsbad Blvd. bridge. Picture 3 - Upstream view of the north bound Carlsbad Blvd. bridge. Picture 4 - Upstream view of the railroad bridge. Picture 5 - Downstream view of Hwy 5 bridge- Picture 6 - Downstream view of the floodplain from El Camino Real bridge. .- Picture 7 - Downstream view of El Camino Real bridge. Picture 8 - Upstream view of the channel from El Camino Real bridge. Picture 9 - View of the channel from Navarra Drive on the left overbank. Picture 10 - Downstream view of the channel just upstream of Rancho La Costa golf course. ,-- Picture 11 - Upstream view of the channel from Piragua Street. _- Picture 12 - Upstream view of the channel at the confluence with it's tributary. /-- Picture 13 - Downstream view of Rancho Santa Fe Road. _- Picture 14 - Downstream view of Rancho Santa Fe bridge.