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HomeMy WebLinkAbout; Agua Hedionda Creek Flood Plain Information; Agua Hedionda Creek Flood Plain Information; 1973-07-01SFC FLOOD PLAIN INFORMATION AGUA HEDIONDA GREEK PACIFIC OCEAN TO BUENA SAN DIEGO COUNTY, CALIFORNIA PREPARED FOR SAN DIEGO COUNTY BY THE DEPARTMENT OF THE ARMY, LOS ANGELES DISTRICT, CORPS OF ENGINEERS LOS ANGELES, CALIFORNIA JULY 1973 CONTENTS Page PREFACE i BACKGROUND INFORMATION 1 Settlement 1 The Streams and Their Valleys 1 Developments on the Flood Plain 2 FLOOD SITUATION 4 Sources of Data and Records 4 Flood Season and Flood Characteristics 5 Factors Affecting Flooding and Its Impact 5 Obstructions to floodflows 5 Flood damage reduction measures 5 Other factors and their impacts 10 Flood warning and forecasting 10 Flood fighting and emergency evacuation plans 10 Floatable material stored on the flood plain 11 PAST FLOODS 12 Summary of Historical Floods 12 Flood Records 12 Flood Descriptions 12 FUTURE FLOODS 14 Intermediate Regional Flood 14 Standard Project Flood 15 Frequency 16 Hazards of Large Floods 16 Flooded areas and flood damages 16 Obstructions 17 Velocities of flow 17 Rates of rise and duration of flooding 19 Photographs, future flood heights 20 GLOSSARY 23 CONTENTS (Continued) PLATES Plate 1 General Map Opposite Preface 2 Index - Flooded Area Follows Text 3-8 Flooded Areas At end of report 9-15 High Water Profiles At end of report 16 Selected Cross Sections At end of report COVER PHOTOGRAPH Outlet of Agua Hedionda Lagoon into the Pacific Ocean, looking downstream. CONTENTS (Continued) TABLES Table Page 1 Drainage Areas 2 2 Stream-Gaging Stations 4 3 Peak Flows for Intermediate Regional and Standard Project Floods 15 4 Bridges and Culverts Within Study Area 18 5 Velocity of Flow 19 6 Rates of Rise and Duration 20 FIGURES Figure 1 Pacific Coast Highway bridge 6 2 Atchison Topeka & Sante Fe Railway Co. bridge over Agua Hedionda 6 3 Interstate 5 bridge over Agua Hedionda Lagoon 7 4 El Camino Real bridge 7 5 Rancho Carlsbad Drive bridge 8 6 Concrete weir at Rancho Carlsbad Drive (East) 8 7 Robelini Drive crossing over Buena Creek 9 8 Atchison Topeka & Santa Fe Railway Co. bridge over Buena Creek 9 9 Future flood heights at Shelter Cove in city of Carlsbad 21 10 Future flood heights at Rancho Carlsbad Drive crossing in Rancho Carlsbad Mobile Home Park, city of Carlsbad 22 11 Future flood heights at Robelini Drive crossing Buena Creek 22 STUDY AREA VICINITY MAP 0 CE AN SI DE W1LDWOOD PARK U S HIGHWAY STATE HIGHWAY CITY LIMITS STREAM GAGE STREAM STREAM MILES DRAINAGE AREA BOUNDARY CARLSBAD RANCHO CARLSBAD . MOBILE PARK OF THE ARMY DISTR.CT, CORPS OF ENG.NEERS i CAL1FORNIA OAKLAKEi RANCH <\\.*-SHELTER // COVE FLOOD PLAIN INFORMATION AGUA HEDIONDA CREEK PACIFIC OCEAN TO BUENA SAN DIEGO COUNTY, CALIFORNIA GENERAL MAP JULY 1973 PLATE I~CI?Y~OF CARUSBACJ CQUNTYQF PREFACE The portion of the City of Carlsbad and San Diego County covered by this report is subject to flooding from Agua Hedionda Creek and one of its tributaries, Buena Creek. The properties along these streams are primarily agricultural with increasing residential use; the damage sustained in past floods has been light. The open space areas in the flood plains that may come under pressure for future development are extensive. This report has been prepared because a knowledge of flood potential and flood hazards is important for land use planning and in arriving at management decisions concerning flood plain utilization. It includes a history of flooding in and around the study area and identifies those areas that are subject to possible future floods. Special emphasis is given to these floods through maps, photographs, profiles, and cross sections. The report does not provide solutions to flood problems; however, it does furnish a suitable basis for the adoption of land use controls to guide flood plain development and thereby prevent intensification of loss problems due to flooding. It will also aid in the identification of other flood damage reduction techniques such as works to modify flooding or adjustments like f/oodproofing, which might be embodied in an overall Flood Plain Management program. Other Flood Plain Management program studies -- those of environmental attributes and the current and future land use of the flood plain as part of its surroundings - would also profit from this information. Flood Plain Management can help prevent future flood losses, since large floods have occurred in the past and studies indicate that even larger floods are possible. At the request of the San Diego County Department of Sanitation and Flood Control and endorsement of the Department of Water Resources, State of California, this report was prepared by the Corps of Engineers, Los Angeles District, under the continuing authority provided in Section 206 of the 1960 Flood Control Act, as amended. The assistance and cooperation of the San Diego County Department of Sanitation and Flood Control, the California Division of Highways, the Oceanside Blade-Tribune Newspaper, the Carlsbad Journal Newspaper, the Vista Press Newspaper, and individuals who directly or indirectly aided in the preparation of this report, are gratefully acknowledged. Additional copies of this report can be obtained from the San Diego County Department of Sanitation and Flood Control. The Corps of Engineers, Los Angeles District, upon request, will provide technical assistance to planning agencies in the interpretation and use of the data presented as well as planning guidance and further assistance, including the development of additional technical information. BACKGROUND INFORMATION Settlement About one-half of the study reach of Agua Hedionda Creek lies within the City of Carlsbad; the remaining area lies within unincorporated San Diego County. The study reach of its main tributary, Buena Creek, lies entirely within unincorporated San Diego County. Most of the land area in the vicinity of the study reaches has been used for agricultural purposes in the past, although ranching was the first major use of the land with the establishment of the large Spanish land grants in the early nineteenth century. Ranching, which was introduced by the Spanish founders of California, never did lead to self-sufficiency; so crop-raising and other agricultural uses gradually replaced ranching as the significant land use. The self-sufficiency of agriculture, mixed with light ranching, had already been demonstrated at the various missions established in the San Diego area. With some exceptions, the land continues in agricultural use today, obviously because water is readily available and there is extensive arable land on the flood plain. However, pressure from developers would result in increased residential use in the near future, especially on the flood plains within the City of Carlsbad where the population is expected to increase rapidly by 1980. The Streams and Their Valleys Agua Hedionda Creek and a major tributary, Buena Creek, drain an area of 29 square miles. The drainage area (see pi. 1) is bounded on the north by a range of hills just south of State Highway 78; on the south by Palomar Airport Road; on the northeast by San Marcos Mountains; and on the west by the Gulf of Santa Catalina in the Pacific Ocean. Agua Hedionda Creek originates in the hills south of the San Marcos Mountains and flows in a general southwest direction, confluencing with Buena Creek about 3 miles downstream. From the confluence, it flows generally westward about 6 miles and enters Agua Hedionda Lagoon, from which it discharges into the Pacific Ocean some 2 miles farther downstream. The stream gradients along Agua Hedionda Creek range from about 43 feet per mile in the upper reaches of the study to about 35 feet per mile in the lower reaches approaching the lagoon. There is an extremely steep canyon reach between mile 5.2 and mile 6.0 along Agua Hedionda Creek which is called Los Monos Canyon. Stream gradients in this reach average 180 feet per mile. Buena Creek, with a drainage area of about 6 square miles, originates in the San Marcos Mountains and flows about 5 miles in a southwest direction before it confluences with Agua Hedionda Creek. The stream gradient of Buena Creek through the study reach is about 51 feet per mile. The climate varies from warm summers to cool winters. Extremes in temperature are rare. Mean seasonal precipitation for the drainage area ranges from about 11 inches near the coast to about 18 inches in higher mountains and averages about 13 inches over the total drainage area. Most of the precipitation occurs during December through March. Snow is not considered an important contributing factor to runoff. Drainage areas upstream from several points along Auga Hedionda Creek and along Buena Creek, its tributary, are shown in table 1. TABLE 1 DRAINAGE AREAS Drainage Ares Location (sq. mi.) Agua Hedionda Creek: At entrance to Lagoon 27.9 D.S. from Calavera Lake Creek 23.3 At mouth of Los Monos Canyon (mile 5.2) 15.3 D.S. from confluence with unnamed tributary 11.4 D.S. from Highway 78 1.9 Buena Creek: Upstream from confluence with Agua Hedionda Creek 6.3 At upstream limit of study 2.9 Agua Hedionda Creek, from its origin in the hills south of the San Marcos Mountains to near the upper limits of this study at mile 9.69, is a relatively small but well defined natural channel with steep slopes and virtually no flood plain. From the upstream study limit to where the stream enters Los Monos Canyon, the channel remains well defined, though on a gentler slope, with a relatively narrow flood plain. For its entire distance of more than a mile through Los Monos Canyon. Agua Hedionda Creek becomes a very steep narrow channel with no flood plain. Downstream from Los Monos Canyon, it broadens out into a shallow, wider channel, with gently rolling overbanks, transitioning into an improved channel through Rancho Carlsbad Mobile Park and golf course. Downstream from Rancho Carlsbad Mobile Park, from El Camino Real to Agua Hedionda Lagoon, the natural channel becomes shallow and indistinct, with a very broad flood plain. During large floods, flows exceed the channel capacity and inundate the flood plain before entering Agua Hedionda Lagoon where considerable flood storage occurs. Attenuated peak floodflows then discharge into the Pacific Ocean, the lower limits of this study. Natural vegetation is abundant, consisting mostly of native grasses, brush, and trees. Relatively dense chapparal predominates in the higher reaches, yielding to sage in the lower reaches of tideland flats along the coast. Developments on the Flood Plain Except for the area around Agua Hedionda Lagoon and for a short reach upstream from El Camino Real, the land in the flood plain of Agua Hedionda Creek is relatively undeveloped. Only about five percent of the approximately 700 acres in the flood plains in this study can be considered as developed. There is a small number of scattered ranches in the upper middle reaches of Agua Hedionda Creek, excluding the virtually undevelopable steep reach of Los Monos Canyon. Crop cultivation and grazing constitute the bulk of the development on the ranches in this flood plain area. Just upstream from El Camino Real, Rancho Carlsbad, a mobile park and golf course, has recently been developed where Sinforosa Country Club was previously located. (See pi. 5.) Horse training facilities are present at Rancho Carlsbad. A small private dam, with a concrete spillway at Oak Lake Ranch just upstream from the mobile park, provides private recreational opportunities in addition to a source of water, which is needed for ranching activities. Agua Hedionda Lagoon has been improved for public fishing at the downstream end of the study reach near Carlsbad Boulevard, (see pi. 3 and 4.) There is a YMCA aquatic park at Agua Hedionda Lagoon between the Atchison, Topeka and Santa Fe Railway and Interstate Highway 5. This park has boating, picnic, water skiing, and other recreational facilities and is used through the courtesy of the San Diego Gas and Electric Company, who owns the property. In general, Agua Hedionda Lagoon is one of the area's outstanding recreational assets which has gained national fame as a water sports area. It has two boat landings, swimming, fishing, sailing and water skiing. The area surrounding the lagoon abounds with private residences but, because of the steepness of the lagoon banks, all these residences are outside of the flood plain. Privately owned, operated, and maintained boat launching and docking facilities are upstream from Interstate Highways. In addition, several apartment buildings and condominiums have been built; and the Carlsbad Chamber of Commerce projects that many more will be constructed in the near future. The entire lagoon area immediately outside of the Agua Hedionda Creek flood plain is a highly developed area. In addition to heavy residential development, there are commercial developments and limited industrial developments. These include service stations, restaurants, grocery stores, banks, an electrical substation, storage facilities, and utility distribution facilities owned and operated by San Diego Gas and Electric Company. Almost one-half of all the persons residing in the entire study area live in the vicinity of Agua Hedionda Lagoon in the City of Carlsbad. FLOOD SITUATION Sources of Data and Records No stream gages exist along Agua Hedionda Creek and Buena Creek. Consequently, no records of past flood peaks were available for frequency analysis of streamflow in these study reaches. Interviews with local residents, research of newspaper files and historical documents, and reports of other governmental agencies revealed little information on past floods that could be used in flood frequency analysis. However, there are records for several gages in nearby basins. (See table 2.) Data from these gages were adjusted to the study area of Agua Hedionda Creek and its studied tributary for hydrologic computations because the physiographic and meteorologic characteristics of these basins are similar to those of the Agua Hedionda Creek basin. TABLE 2 STREAM-GAGING STATIONS Drainage Area Period of Maximum Recorded Stream Gage (sq. miles) Record Peak Flow C.F.S. Date Buena Vista Creek in Wildwood Park 4.3 1963-1971 162 Feb. 1969 Los Flores Creek near Oceanside 26.6 1952-1970 4,200 Feb. 1969 San Onofre Creek near San Onofre 34.6 1951-1967 2,680 Apr. 1958 De Luz Creek near Fallbrook 47.9 1951-1969 7,800 Feb. 1970 San Juan Creek near San Juan Capistrano 106.0 1929-1971 22,400 Feb. 1969 The maps prepared for this report were based on maps supplied by the San Diego County Department of Sanitation and Flood Control and by the City of Carlsbad. Structural data on bridges and culverts were furnished jointly by the California Division of Highways and the San Diego County Department of Sanitation and Flood Control. Supplemental information was obtained in the field by Corps of Engineers personnel during the course of the study. Overflow areas, cross sections, and stream profiles were developed from this collective data. Flood Season and Flood Characteristics Major floods have occurred along Agua Hedionda Creek and its tributaries, as well as in the adjacent basins (table 2), during both the winter and summer months, although most of the precipitation occurs during the period of December to April. Rainless periods of several months during the summer are common. Three types of storms produce precipitation in the area: general winter storms; general summer storms; and thunderstorms. The storm selected as critical for the watershed, producing the largest peak discharge, is a high intensity, 3-hour thunderstorm. Runoff from such cloudbursts is characterized by high peak flows, short duration of flows, and relatively small volumes. Snow is not considered an important contributory factor to runoff in the basin. Also, climatic and drainage area characteristics are not conducive to continuous flow. Consequently, little streamflow occurs, except during and immediately following rains. Runoff increases rapidly in response to rainfall excess. Factors Affecting Flooding and Its Impact Obstructions to floodflows - Natural obstructions to floodflows include trees or dense vegetation growing along the streambanks or on the flood plain. Manmade obstructions include the bridges and culverts listed in table 4, in addition to numerous small private bridges and low flow culverts of insignificant size. These insignificant stream crossings would be scoured out and washed downstream, further contributing to flood debris during any major flood. Other manmade obstructions consist of water and sewer pipelines across the flood plain. In general, obstructions restrict floodflows and result in overbank flows and unpredictable areas of flooding, destruction of or damage to bridges and culverts, and increased velocity of flow immediately downstream. The major obstructions to floodflows in the study area are shown in figures 1 through 8. During floods, obstructions in the channel and overbank impede floodflows, thus creating backwater and increased flood heights. Brush and trees may be washed away and carried downstream to collect on bridges and on other obstructions to flow. As floodflow increases, masses of debris may break loose and a wall of water and debris could surge downstream until another obstruction is encountered. Debris may collect against a bridge, creating a damming effect, until the load exceeds its structural capability and the bridge is destroyed. The limited capacity of obstructive bridges retards floodflows and results in flooding upstream, erosion around bridge approach embankments, and possible damage to the overlying roadbed. Flood damage reduction measures - The San Diego Gas and Electric Company has constructed rock groins at the outlet of Agua Hedionda Lagoon into the Pacific Ocean. There are no Corps of Engineers projects or other Federal flood damage prevention projects; and none are contemplated in the foreseeable future. There are several reaches of improved channel and other flood damage prevention measures along the study reaches. The rock groins at the outlet of the lagoon into the Pacific Ocean serve to protect the shoreline and Figure 1 — Pacific Coast Highway bridge (looking upstream). This point marks the mouth of Agua Hedionda Lagoon. Figure 2 — Atchison Topeka and Sante Fe Railway Co. bridge over Agua Hedionda Lagoon (looking upstream). . Figure 3 — Interstate 5 bridge over Agua Hedionda Lagoon (looking upstream). Figure 4 — El Camino Real bridge (looking upstream). J Figure 5 — Rancho Carlsbad Drive bridge (looking upstream). Concrete drop structures in foreground. Figure 6 — Concrete weir at Rancho Carlsbad Drive (East) (looking downstream). 8 - Figure 7 — Robelini Drive crossing over Buena Creek (looking upstream). Figure 8 — Atchison Topeka and Sante Fe Railway Co. bridge over Buena Creek (looking downstream). the banks of the lagoon from scour damage. Such scour damage can be due to tidal wave action, as well as to the relatively high velocity of floodflows discharging into'the ocean. Chained logs at several places in the lower lagoon aid deposition of heavy debris for subsequent clearing or removal. In this way, possible damage to bridges and lagoon banks by high velocity debris traveling through the lagoon is averted. The banks of the lower lagoon area as far upstream as the Atchison, Topeka and Santa Fe Railway have been stabilized by rock revetment. About one-half mile of improved earth channel has been constructed by the Rancho Carlsbad Development Company through a mobile home park upstream from El Camino Real. This channel has the capacity to contain the 100-year flood, although scour damage to the banks and streambed would occur from the 100-year flood and from larger floods because of high velocities of flow in the channel. However, such damage would be limited because of the stabilizing influence of a concrete drop structure and a weir within this reach. Along Buena Creek, there are about 500 feet of improved earth channel upstream from the culvert crossing under State Highway 78. This reach of improved channel was constructed by the California State Division of Highways to channelize flow into the culvert. However, both the Intermediate Regional and Standard Project Floods are too large to be contained within this channel. Other Factors and Their Impacts Flood warning and forecasting - The County of San Diego Department of Sanitation and Flood Control maintains surveillance during a storm by monitoring a weather teletype system. About two dozen rain, stream, and reservoir gages are monitored in San Diego County, providing current information about storm and flooding conditions. Additional information is provided through coordination with the National Weather Service office in San Diego and with the California State Department of Water Resources River Forecast Center. Although specific flood forecasts are not made for the Agua Hedionda Creek drainage basin, daily weather forecasts applicable to the area are issued by the National Weather Service office in San Diego. Flood fighting and emergency evacuation plans - There are no specific flood fighting or emergency evacuation plans for the study area. If the need arises, State and local law enforcement agencies, local fire departments, civil defense groups, and street and highway maintenance crews could assist in the rescue of stranded persons and perform other flood fighting activities. The California State Department of Water Resources, through its Flood Operations Center, coordinates flood fighting activities throughout the State and is authorized to receive requests from local public agencies for assistance during floods. During emergencies, the San Diego County Civil Defense and Disaster Office coordinates activities of local law enforcement agencies, and of fire, health, and sanitation departments. The Corps of Engineers responds to requests from the State Disaster Office for assistance in flood fighting and rescue work when flood emergencies are beyond the capabilities of State and local governmental agencies. 10 Floatable material stored on the flood plain - Several boats and other marine recreational craft are anchored in the lagoon. During major floods, these craft could be swept downstream and could clog bridge openings, creating increased flood stages and possibly damaging bridge structures. No other unrestrained floatable objects are known to be on the flood plains of Agua Hedionda Creek and Buena Creek. This is mainly because the principally agricultural and residential uses of the flood plains in the study area do not result in the accumulation of significant amounts of floatable materials that could be carried away by f loodwaters. 11 area. PAST FLOODS Summary of Historical Floods Floods of damaging proportions have occurred in the region which includes the study basin in 1862, 1884, 1895, 1916, 1927, 1932, 1938 and 1942. Although little information is available, indications are that significant inundation occurred in the basin, blocking roads and flooding out farmhouses and crops. However, flood damage from such floods have been relatively light since virtually no high-value developments existed on the flood plain during these floods. Flood Records There are no official records of past floods. Information on historical floods in the study area is very limited due to the absence of streamflow records. Information on historical floods contained in this report is based on research of newspaper accounts and on interviews with local residents and officials. No flow or stage hydrographs are available for the study Flood Descriptions Very few descriptions of past floods that have directly affected the study area are available and no photographs were found. However, the following excerpts from several newspapers in adjacent areas should serve to depict the type fo flood damage which has occurred in the past. EXCERPT FROM THE OCEAIMSIDE BLADE, JANUARY 22, 1916 "For a week San Diego County has been struggling in the grip of a storm and floods that have extended all over the state and that for severity and in point of damage done exceed anything experienced for years past." "The damage up the river from late accounts is principally the destruction of the Bonsall bridge which is entirely gone. The San Luis Rey bridge is unhurt but there is a considerable cut in the approach on the north side which is passable for teams. The roadway is badly damaged at the Monserrate ranch and at the Richman place at Bo.isall. No reports are made of any damage at Pala and Supervisor Westfall who got down Thursday afternoon reports that Fallbrook was unhurt nothing being damaged but small culverts. The rainfall for the storm at Fallbrook was 10.50 inches. The road on the north side of the river can now be used as far as Monserrate from Oceanside." 12 EXCERPT FROM THE CARLSBAD JOURNAL, DECEMBER 8, 1966 "Four inches of rain, half a season's supply in some years, fell in Carlsbad in a major storm which started Saturday." Heavy winds and rains set off a series of minor car accidents, flooded streets and gutters and caused some erosion at construction sites. Buena Vista Lagoon and its eastern flood plain reached full capacity, forcing Carlsbad and Oceanside city crews to open an outlet channel into the ocean. In one wet-weather mishap, two men were taken to Oceanside Community Hospital for treatment. EXCERPT FROM THE VISTA PRESS, DECEMBER 9, 1966 Vista Press, Friday December 9, 1966 "Vista's rainfall total for the recent four-day storm is less than one inch short of the greatest continuous rainfall total recorded here in 36 years, 7.29 inches recorded from February 27 to March 4, 1938." "City crews are now clearing mud from dozens of streets and repairing major washouts. During the storm itself they were called out to remove felled trees in several locations including on Vale Terrace near the Optimist Club that left a portion of the community without power for nearly an hour Tuesday night." 13 FUTURE FLOODS Although floods of the same magnitude as those that have occurred in the past could recur in the future, discussion of the future floods in the report is limited primarily to those that have been designated as the Intermediate Regional and Standard Project Floods. The Standard Project Flood would be larger and would occur less frequently than the Intermediate Regional Flood, and both of these floods would be greater than any known to have occurred in the past. A Standard Project Flood would be a rare event, but could reasonably be expected to occur in the future. Selection of the Intermediate Regional and Standard Project Floods was based on hydrologic computations (correlation of records of similar drainage basins) and consideration of pertinent meteorologic and physiographic conditions. As previously indicated, floods caused by severe local storms can affect large areas of the flood plain, result in greater flood damage, and create greater hazards to people than general winter storms. Therefore, the future floods discussed herein are of the severe local storm type. During floods, debris collecting on bridges and culverts could decrease their carrying capacity and cause greater water depths (backwater effect) upstream from these structures. The occurrence and amount of debris are indeterminate factors; however, a limited amount of debris was considered in preparing profiles of the Intermediate Regional and Standard Project Floods. Similarly, the maps of flooded areas show the backwater effect of obstructive bridges and culverts, and reflect increased water surface elevations that could be caused by limited amounts of debris collecting against the structures. Intermediate Regional Flood The Intermediate Regional Flood is one that could occur about once in 100 years on the average, although it may occur in any year or more than once in one year. Usually the peak flow of such a flood is developed from statistical analyses of streamflow and precipitation records and the runoff characteristics of the stream basin. Since there are no streamflow records for the study reaches, it was necessary to analyze precipitation and streamflow records of other stream basins having hydrologic, meteorologic, and physiographic characteristics similar to those of the Agua Hedionda Creek basin. Studies were made to transpose the information, thus derived to the study basin and to compute peak flows for the Intermediate Regional Flood. Peak flows developed for the Intermediate Regional Flood at selected points in the study area are shown in table 3. Stream-gaging stations for Buena Vista Creek, Los Flores Creek, San Onofre Creek, De Luz Creek and San Juan Creek yielded the data for transposition to the study basin. 14 TABLE 3 PEAK FLOWS FOR INTERMEDIATE REGIONAL AND STANDARD PROJECT FLOODS Location Miles Upstream from mouth Drainage Area (sq.mi.) Intermediate Regional Flood (c.f.s.) Standard Project Flood (c.f.s.) -1 Agua Hedionda Creek: At entrance to lagoon 2.30 Downstream of confluence with Calaveras Lake Creek 3.27 At Los Monos Canyon Mouth 5.21 Downstream of confluence with unnamed tributary 6.83 At Green Oaks Ranch 8.18 Downstream of Highway 78 9.69 Buena Creek: At confluence with Agua Hedionda Creek 0.00 At upstream limit of study 2.69 27.9 23.3 15.3 11.4 9.1 1.9 6.3 2.9 10,500 10,300 7,700 7,000 6,800 1,100* 4,800 3,300 15,000 14,700 11,000 10,000 9,700 1,100* 6,900 4,700 1 *Culvert outflow. Standard Project Flood For the purpose of determining peak flows of the Standard Project Flood, a standard project storml/ was derived for the study basin from statistical analyses of the above-mentioned stream basins having similar meteorologic characteristics. Studies were made to transpose storm data to the basin and compute peak flows for the Standard Project Flood. Peak flows thus developed for the Standard Project Flood at selected points in the study area are shown in table 3. J/ The most severe combination of meteorologic conditions reasonably characteristic of the geographic region, excluding extremely rare combinations. 15 Frequency Because official records of past floods in the basin do not exist, the assignment of frequencies to these floods is not possible. The occurrence of either the Intermediate Regional Flood or the Standard Project Flood in the basin would be a rare event. However, even greater floods, such as the Probable Maximum Flood (see Glossary for definition) are possible. Statistical frequencies of occurrence cannot be assigned to floods of the magnitude of the Standard Project or the Maximum Probable Floods, which are predicted by theoretically synthesizing many climatic and hydrologic factors. Hazards of Large Floods The amount and extent of damage caused by any flood depends on the topography of the area flooded, depth, and duration of flooding, velocity of flow, and developments on the flood plain. An Intermediate Regional or Standard Project Flood on Agua Hedionda and Buena Creeks would result in inundation of most of the riverine lands in the study reaches of these creeks. Limited flooding of agricultural, residential and recreational property would also occur. However, flood damage to residential development would be small because most of the development is located outside of the flood plain. Deep floodwater flowing at a high velocity and carrying floating debris would create conditions hazardous to persons and vehicles attempting to cross flooded areas. In general, floodwater three or more feet deep and flowing at a velocity of three or more feet per second could sweep a person off his feet, thus creating definite dangers of injury or drowning. Rapidly rising and swiftly flowing floodwater may trap persons in homes that are ultimately submerged. Decaying flood-deposited garbage or other organic materials could create hazards in terms of medical or fire emergencies. Flooded areas and flood damages - The areas along Agua Hedionda Creek and along the Buena Creek tributary that would be flooded by a Standard Project Flood are shown on plate 2, which is an index map to plates 3 through 8. Areas that would be flooded by the Intermediate Regional and Standard Project Floods are shown in detail on plates 3 through 8. They include recreational, agricultural, and residential areas and the associated streets, roads, and public utilities. Due to the wider flood plain, greater depth of flooding, higher velocity flow, and longer duration of flooding during a Standard Project Flood, damage would be more severe than during an Intermediate Regional Flood. Streets, bridges, culverts, and public utilities would be severely damaged by high velocity floodflows. Extensive deposits of silt and debris would occur in many parts of the flooded areas. Plates 9 through 15 show water surface profiles of the Intermediate Regional and Standard Project Floods. Depth of flow in the channel can be estimated from these illustrations. Typical cross sections of the flood plain at selected locations, together with the water surface elevation and lateral extent of the Intermediate Regional and Standard Project Floods, are shown on plate 16. Specific damage that would be expected at various locations are listed below: 16 a. Minor damage due to inundation of streets in the Shelter Cove area around Agua Hedionda Lagoon. b. Interruption of traffic along Calaveras Road (see pi. 4) and damage to adjacent ,, property due to flooding up to 6 feet in depth. c. Scour damage to the improved channel through Rancho Carlsbad Mobile Park. Scour damage would also take place to a limited extent in the golf course area of Rancho Carlsbad Mobile Park. Several small foot bridges and crossings would be washed out. d. Several homes and structures along Buena Creek would be flooded and damaged by scour and debris deposition (see pi. 8). e. In addition, several scattered farms and ranches along the middle reaches of Agua Hedionda Creek, including Oak Lake Ranch, would be damaged by inundation and scour. —5 f. Underground pipelines at mile 4.8 and San Diego Gas and Electric overhead pipelines crossing the lagoon are also subject to damage during floods of the magnitude of an Intermediate Regional or Standard Project Flood. Scour damage is likely in the case of the underground pipelines whereas damage from debris deposition is more likely with respect to the overhead pipelines crossing at the railroad bridge over the lagoon. Limits of overflow indicated on plates 3 through 8 may vary from actual locations on the ground due to map scale, deposition, erosion, inaccuracy of original topographic maps, or other causes. Obstructions - Several bridges and culverts cross the study reaches of Agua Hedionda Creek and its studied tributary: These include two railroad bridges, a major interstate freeway bridge, a major highway bridge and several other small bridges and culverts. Table 4 shows the water surface elevations at some of these crossings for the Intermediate Regional and Standard Project Floods. As shown in table 4, all of the bridges have the capacity to convey the Intermediate Regional and Standard Project Floods without being overtopped. However, none of the culverts can pass either of these floods without being severely inundated. It is anticipated that most of the small culverts would be washed out by either the Intermediate Regional or Standard Project Floods. All of these bridges and culverts provide a major obstruction to floodflows, producing a backwater effect. Velocities of flow - Occurrence of the Intermediate Regional or Standard Project Floods would result in the flows shown in table 3. Because of considerable storage of floodwaters in Agua Hedionda Lagoon and due to the relatively large width of flow, the velocity is very low through the lagoon averaging about one foot per second for the Intermediate Regional Flood and about one and one-half feet per second for the Standard Project Flood. During an Intermediate Regional Flood, the average velocity of main channel flow upstream from Agua Hedionda Lagoon would range from 10 to 12 feet per second. Water flowing at this rate is capable of causing erosion to streambanks and transporting large rocks. . 17 TABLE 4 BRIDGES AND CULVERTS WITHIN STUDY AREA Identification Agua Hedionda Creek: Pacific Coast Highway Bridge Atchison Topeka & Sante Fe Railroad Bridge Interstate 5 Bridge El Camino Real Bridge Rancho Carlsbad Drive Bridge Buena Creek: State Highway 78 Culvert (triple 10'x6' RCB) State Highway 78 Overpass Robelini Drive Culvert (doube48 inch CMP) Mission Road Culvert (double 5'x5' RCB) Atchison Topeka & Santa Fe Bridge Elevation (b) Low Location Streambed Chord Roadway IRF* SPF** (a) (c) (d) (e) (e) 0.06 0.51 0.72 3.22 3.72 1.36 1.36 1.86 2.04 2.11 0.0 13.4 389.5 395.5 389.5 416.0 416.0 420.0 431.0 436.0 434.9 446.2 18.0 5.8 6.0 0.0 0.0 31.6 44.0 28.4 25.7 42.8 56.0 30.0 27.8 45.9 59.0 7.4 8.5 40.2 54.5 9.0 10.3 42.0 56.0 400.0 401.2 402.2 419.0 401.2 402.5 422.5 431.8 433.0 441.0 442.4 443.5 448.0 448.3 449.1 (a) Miles upstream from mouth. (b) All elevations are in feet, mean sea level datum. (c) Elevation of bottom of bridge structure or top of culvert. (d) Average elevation. (e) Computed water surface elevation based on estimated flow and existing channel and structures. * Intermediate Regional Flood ** Standard Project Flood In the steep canyon section of Los Monos Canyon, velocities could reach 22 feet per second; this would cause severe erosion and would dislodge and move large boulders. The average velocities in the Buena Creek reach studied would range from about 9 to 13 feet per second during an Intermediate Regional Flood. It is expected that velocity of flow during a Standard Project Flood would be slightly higher than that during an Intermediate Regional Flood. Water flowing at about two feet per second or less would deposit debris and silt. Table 5 shows average velocities at several points in the study area. 18 TABLE 5 VELOCITY OF FLOW Stream and Location Miles Intermediate Upstream Regional Flood From Channel Overbank Mouth fps fps Standard Project Flood Channel Overbank fps fps Agua Hedionda Creek: Upstream from El Camino Real 4.68 Upstream of confluence with unnamed wash at mile 5.20 5.62 Upstream of confluence with unnamed wash at mile 6.80 6.90 Upstream of confluence with Buena Creek Trib. 8.85 Buena Creek: At Section 6 1.04 12 15 13 10 9 8 8 5 3 12 17 15 11 10 9 10 6 4 Rates of rise and duration of flooding - Intense rainfall from severe local storms and general winter storms centered over the upper reaches of the basin collects rapidly as surface runoff and reaches the Pacific Ocean after being routed through Agua Hedionda Lagoon. Most local storms last for only a few hours. Consequently, the total volume of runoff is relatively small, and the duration of overflows is short. For the Intermediate Regional and Standard Project Floods just downstream of El Camino Real, table 6 gives the height of rise (from flood stage level to maximum floodflow level), time of rise (time period corresponding to height of rise), and duration of flood stage (period of time flooding is above flood stage level). 19 TABLE 6 RATES OF RISE AND DURATION (at Pacific Coast Highway) Flood Intermediate Regional Standard Project Height of Rise (Feet) 2.9 4.0 Time of Rise (Hours) 1.9 21. Duration of Flood Stage (Hours) 3.4 4.0 On the average, the water surface elevation of the Standard Project Flood on Agua Hedionda Creek would be about one and one-half feet higher than that of the Intermediate Regional Flood, except in the lagoon area where the Standard Project Flood averages about 2 feet higher than the Intermediate Regional Flood. For Buena Creek tributary, the water surface elevation of the Standard Project Flood would average about one foot higher than that of the Intermediate Regional Flood. Photographs, future flood heights - The levels that the Intermediate Regional and Standard Project Floods are expected to reach at various locations on the Agua Hedionda Creek flood plain, are indicated on the following photographs (figures 9 to 11). 20 STANDARD PROJECT ROOD-*" INTERMEDIATE REGIONAL FLOOD STANDARD PROJECT FLOOD-W INTERMEDIATE REGIONAL FLOO0"-S» Figure 9 — Future flood heights at Shelter Cove (west side) in city of Carlsbad (see magnified view above). 21 4 STANDARD PROJECT ROOD •'lif/yrssjifmrnammm. •<- ««*»»»> INTERMEDIATE REGIONAL FLOOD Figure 10 — Future flood heights at Rancho Carlsbad Drive crossing in Rancho Carlsbad Mobile Home Park, city of Carlsbad. STANDARD PROJECT FLOOD BGSQHIIIIBKQN^L, ! I INTERMEDIATE REGIONAL FLOOD Figure 11 Creek. — Future flood heights at Robelini Drive crossing Buena 22 GLOSSARY Backwater - The resulting high water surface in a given stream due to a downstream obstruction or high stage in an intersecting stream. Flood - An overflow of lands not normally covered by water and that are used or usable by man. Floods have two essential characteristics: The inundation of land is temporary; and the land is adjacent to and inundated by overflow from a river or a stream, an ocean or a lake or other body of standing water. Normally, a "flood" is considered as any temporary rise in streamflow or stage (not the ponding of surface water) that results in significant adverse effects in the vicinity. Adverse effects may include damages from overflow of land areas, temporary backwater effects in sewers and local drainage channels, creation of unsanitary conditions or other unfavorable situations by deposition of materials in stream channels during flood recessions, rise of ground water coincident with increased streamflow, and other problems. Flood Crest - The maximum stage or elevation reached by the waters of a flood at a given location. Flood Peak - The maximum instantaneous discharge of a flood at a given location. It usually occurs at or near the time of the flood crest. Flood Plain - The relatively flat area or lowlands adjoining the channel or a river, a stream, or a watercourse, an ocean, or a lake or other body of standing water that have been or may be covered by f loodwater. Flood Profile - A graph showing the relationship of water surface elevation to location, the latter generally expressed as distance above mouth for a stream of water flowing in an open channel. It is generally drawn to show surface elevation for the crest of a specific flood, but may be prepared for conditions at a given time or stage.1 Flood Stage - The stage or elevation at which overflow of the natural banks of a stream or body of water begins in the reach or area in which the elevation is measured. Flood Stage Level - The elevation that corresponds to flood stage. . Floodway - The channel of the stream and that part of the flood plain that would be used to carry floodflows. General Winter Storm - A widespread storm usually occurring in the months of December through March, characterized by heavy and prolonged rainfall over a large area. 23 Intermediate Regional Flood - A flood having an average frequency of occurrence of once in 100 years, although the flood may occur in any year or more than once in one year. It is based on statistical analyses of streamflow records available for the watershed and analyses of rainfall and runoff characteristics in the general region of the watershed. Probable Maximum Flood - A hypothetical flood representing the most severe flood with respect to volume, concentration of runoff, and peak discharge that may be expected from a combination of the most severe meteorologic and hydrologic conditions in the region. Standard Project Floods - The flood that may be expected from the most severe combination of meteorologic and hydrologic conditions that is considered reasonably characteristic of the geographic area in which the drainage basin is located, excluding extremely rare combinations. Peak discharges for these floods are generally about 40 to 60 percent of the Probable Maximum Floods for the same basins. As used by the Corps of Engineers, Standard Project Floods are intended as practicable expressions of the degree of protection that should be sought in the design of flood control works, the failure of which might be disastrous. Thunderstorm - A high-intensity, convective-type rainstorm of short duration that is characterized by extremely heavy rainfall. As used in this report, "severe local storm" and "thunderstorm" are essentially synonymous. 24 STUDY AREA VICINITY MAP VISTA OCEANSIDE U S HIGHWAY STATE HIGHWAY • MTY LIMITS STREAM GAGE STREAM STREAM MILES A LAGOON [~~~1 AREA FLOODED BY STANDARD PROJECT FLOOD. si CARLSBAD DEPARTMENT OF THE ARMY LCS ANGELES DISTRICT, CORPS OF ENGINEERS LOS ANGELES, CALIFORNIA FLOOD PLAIN INFORMATION AGUA HEDIONDA CREEK SAN DIEGO COUNTY, CALIFORNIA INDEX MAP - FLOODED AREA JULY 1973 PLATE 2 ,„ _\ jJ%-Z'\ \ s «« Xt> ' LEGEND:OVERFLOW LIMITS j INTERMEDIATE j REGIONAL FLOOD STANDARD PROJECT FLOOD 2.50 MILES ABOVE MOUTH [T) — CROSS SECTION 400 GROUND ELEVATION IN FEET ABOVE MEAN SEA LEVEL CONTOUR INTERVAL Z FEET NOTES: LIMITS OF OVERFLOW INDICATED MAY VARY FROM ACTUAL LOCATIONS ON GROUND, AS EXPLAINED IN THE REPORT. DATE OF TOPOGRAPHY I960 BASE TOPOGRAPHIC MAPS FURNISHED BY CITY OF CARLSBAD AREAS OUTSIDE THE FLOOD PLAIN HAY BE SUBJECT TO FLOODING FROM LOCAL RUNOFF 600SCALE! DEPARTMENT Of THE ARMY LOS ANGELES DISTRICT, CORPS OF ENGINEERS LOS ANGELES. CALIFORNIA FLOOD PLAIN INFORMATION AQUA HEDIONDA CREEK SAN DIEGO COUNTY, CALIFORNIA FLOODED AREAS JULY 1973 PLATE 3 LEGEND: CITY; OF CARLSBAD immMSffi OVERFLOW LIMITS ) INTERMEDIATE J REGIONAL FLOOD STANDARD PROJECT FLOOD M+ 2.50 MILES ABOVE MOUTH l CROSS SECTION )/f 400 GROUND ELEVATION IN FEET ABOVE MEAN SEA LEVEL CONTOUR INTERVAL 5 FEET LIMITS OF OVERFLOW INDICATED MAY VARY FROM ACTUAL LOCATIONS ON GROUND, AS EXPLAINED IN THE REPORT. DATE OF TOPOGRAPHY I960 TO 1963 BASE TOPOGRAPHIC MAPS FURNISHED BY POUNTY OF SAN DIEGO AND CITY OF CARLSBAD AREAS OUTSIDE THE FfcOOO PLAIN MAY BE SUBJECT TO FLOODING FROM LOCAL HVM0FF N I \\ \ DEPARTMENT OF THE ARMY LOS ANGELES DISTRICT, CORPS OF ENGINEERS LOS ANGELES, CALIFORNIA FLOOD PLAIN INFORMATION AGUA HEDIONDA CREEK SAN DIEGO COUNTY, CALIFORNIA FLOODED AREAS JULY 1973 PLATE 4 LEGEND:OVERFLOW LIMITS ) INTERMEDIATE ) REGIONAL FLOOD STANDARD PROJECT FLOOD 2.50 ____ MILES ABOVE MOUTH — - - CROSS SECTION 400 ________ GROUND ELEVATION IN FEET ABOVE MEAN SEA LEVEL CONTOUR INTERVAL 5 FEET NOTES: LIMITS OF OVERFLOW INDICATED MAY VARY FROM ACTUAL LOCATIONS ON GROUND, AS EXPLAINED IN THE REPORT. DATE OF TOPOGRAPHY 1960 TO 1963 BASE TOPOGRAPHIC MAPS FURNISHED BY COUNTY OF SAN DIEGO AREAS OUTSIDE THE FLOOD PLAIN MAY BE SUBJECT TO FLOODING FROM LOCAL RUNOFF 600 SCALE| DEPARTMENT OF THE ARMY LOS ANGELES DISTRICT, CORPS OF ENGINEERS LOS ANGELES, CALIFORNIA FLOOD PLAIN INFORMATION AGUA HEDIONDA CREEK SAN DIEGO COUNTY, CALIFORNIA FLOODED AREAS JULY 1973 PLATE 5 LEGEND:OVERFLOW LIMITS } INTERMEDIATE ) REGIONAL FLOOD STANDARD PROJECT FLOOD 2.50 MILES ABOVE MOUTH HO™ CROSS SECTION 400 GROUND ELEVATION IN FEET ABOVE MEAN SEA LEVEL ^ CONTOUR INTERVAL 5 FEET NOTES: LIMITS OF OVERFLOW INDICATED MAY VARY FROM ACTUAL LOCATIONS ON GROUND, AS EXPLAINED IN THE REPORT. DATE OF TOPOGRAPHY I960 TO 1963 BASE TOPOGRAPHIC MAPS FURNISHED BY COUNTY OF SAN DIEGO AREAS OUTSIDE THE FLOOD PLAIN MAY BE SUBJECT TO FLOODING FROM LOCAi RUNOFF \^^ 600 SCALE( DEPARTMENT OF THE ARMY LOS ANGELES DISTRICT, CORPS OF ENGINEERS LOS ANGELES, CALIFORNIA FLOOD PLAIN INFORMATION AGUA HEDIONDA CREEK SAN DIEGO COUNTY, CALIFORNIA FLOODED AREAS JULY 1973 PLATE 6 1 I i\lP ) * Vtft LEGEND:OVERFLOW LIMITS INTERMEDIATE \ REGIONAL FLOOD STANDARD PROJECT FLOOD 2.50 MILES ABOVE MOUTH CROSS SECTION 400 GROUND ELEVATION IN FEET ABOVE MEAN SEA LEVEL CONTOUR INTERVAL 5 FEET LIMITS OF OVERFLOW INDICATED MAY VARY FROM ACTUAL LOCATIONS ON GROUND, AS EXPLAINED IN THE REPORT. DATE OF TOPOGRAPHY 1958 TO 1960 BASE TOPOGRAPHIC MAPS FURNISHED BY AREAS OUTSIDE THE FLOOD PLAIN MAY BE SUBJECT TO FLOODING FROM LOCAL RUNOFF N i 600 SFEET DEPARTMENT OF THE ARMY LOS ANGELES DISTRICT, CORPS OF ENGINEERS LOS ANGELES, CALIFORNIA FLOOD PLAIN INFORMATION AGUA HEDIONDA CREEK & BUENA CREEK TRIBUTARY SAN DIEGO COUNTY, CALIFORNIA FLOODED AREAS JULY 1973 PLATE 7 LEGEND:OVERFLOW LIMITS I INTERMEDIATE ) REGIONAL FLOOD STANDARD PROJECT FLOOD 2.50 MILES ABOVE MOUTH [Tj CROSS SECTION 400 GROUND ELEVATION IN FEET ABOVE MEAN SEA LEVEL CONTOUR INTERVAL 5 FEET NOTES: LIMITS OF OVERFLOW INDICATED MAY VARY FROM ACTUAL LOCATIONS ON GROUND, AS EXPLAINED IN THE REPORT. DATE OF TOPOGRAPHY 1958 TO I960 BASE TOPOGRAPHIC MAPS FURNISHED BY COUNTY OF SAN DIEGO AREAS OUTSIDE THE FLOOO PLAIN MAY BE SUBJECT TO FLOODING FROM LOCAL fiUNOFF 600 SCALE I 600 I FEET DEPARTMENT OF THE ARMY LOS ANGELES DISTRICT, CORPS OF ENGINEERS LOS ANGELES, CALIFORNIA FLOOD PLAIN INFORMATION AGUA HEDIONDA CREEK & BUENA CREEK TRIBUTARY SAN DIEGO COUNTY, CALIFORNIA FLOODED AREAS JULY 1973 PLATE 8 CO s t- LU LU U. Zo UJ _J UJ 60 DEPARTMENT OF THE ARMY LOS ANGELES DISTRICT, CORPS OF ENGINEERS LOS ANGELES, CALIFORNIA 2.0 0.0 0.5 FLOOD PLAIN INFORMATION SAN DIEGO COUNTY, CALIFORNIA HIGH WATER PROFILES AQUA HEDIONDA CREEK JULY 1973 1.0 MILES ABOVE MOUTH 1.5 PLATE 9 !3 H < UJ UJLL o h-2 UJ_l UJ _L_1-4-4—U4 J 1 J i 4J- • -1 •- T 1...L.L..1. DEPARTMENT OF THE ARMY LOS ANGELES DISTRICT, CORPS OF ENGINEERS LOS ANGELES, CALIFORNIA 20 10 0 2.0 2.5 3.0 MILES ABOVE MOUTH 3.5 FLOOD PLAIN INFORMATION SAN DIEGO COUNTY, CALIFORNIA HIGH WATER PROFILES AGUA HEDIONDA CREEK JULY 1973 PLATE 10 120 MO IOO Q J CO iu UJ 2o UJ_J LU " \ t TT i T\ i—f—t—+~i- - - ; i f—|,;lntermediiat| Regional Flood '^LLJUM < ! j-+--I r-t -t—J - } : 1 • Streambe i;i * " 6.0 50 4O 4.O 5.0 MILES ABOVE MOUTH DEPARTMENT OF THE ARMY LOS ANGELES DISTRICT, CORPS OF ENGINEERS LOS ANGELES, CALIFORNIA FLOOD PLAIN INFORMATION SAN DIEGO COUNTY, CALIFORNIA HIGH WATER PROFILES AQUA HEDIONDA CREEK JULY 1973 PLATE 11 330 320 Io 310 300 UJ LU o1 LU_J LU 290 280 270 260 250 8.0 6.0 6 .5 7.0 MILES ABOVE MOUTH 7.5 DEPARTMENT OF THE ARMY LOS ANGELES DISTRICT, CORPS OF ENGINEERS LOS ANGELES, CALIFORNIA FLOOD PLAIN INFORMATION SAN DIEGO COUNTY, CALIFORNIA HIGH WATER PROFILES AQUA HEDIONDA CREEK JULY 1973 PLATE 12 400 390 s I- Q J c/i 5 LUu. Z 2O UJ_i UJ 380 370 360 350 340 330 320 8.0 IrWsrniecToije M- h-r DEPARTMENT OF THE ARMY LOS ANGELES DISTRICT, CORPS OF ENGINEERS LOS ANGELES, CALIFORNIA 10.0 9.0 MILES ABOVE MOUTH 9.5 FLOOD PLAIN INFORMATION SAN DIEGO COUNTY, CALIFORNIA HIGH WATER PROFILES AGUA HEDIONDA CREEK JULY 1973 PLATE 13 420 410 400 390 h= Q 380t- LU LU O 370 <.> LU 5ycainoJ"e j—*- t— F > 10X6 RClB/ I 1 1 4-I I I ! DEPARTMENT.OF THE ARMY LOS ANGELES DISTRICT, CORPS OF ENGINEERS LOS ANGELES, CALIFORNIA 360 330 0.0 .5 MILES ABOVE CONFLUENCE 2,0 FLOOD PLAIN INFORMATION SAN DIEGO COUNTY, CALIFORNIA HIGH WATER PROFILES BUENA CREEK (TRIBUTARY) JULY 1973 PLATE 14 490 480 Q J LU UJ 470 O 460 UJ_j UJ 45© ,0 2.5 3.0 MILES ABOVE CONFLUENCE DEPARTMENT OF THE ARMY LOS ANGELES DISTRICT, CORPS OF ENGINEERS LOS ANGELES, CALIFORNIA FLOOD PLAIN INFORMATION SAN DIEGO COUNTY, CALIFORNIA HIGH WATER PROFILES BUENA CREEK (TRIBUTARY) JULY \973 PLATE 15 UJ> UJ_1 <lit<f) 2 < UJ UJ oCD UJ UJu. o1 UJ_]UJ CROSS SECTION NO. I MILE 1.00 90 85 80 CROSS SECTION NO. 2 MILE 4.68 0 CROSS SECTION N0.3 MILE 5.62 315 310 305 300 295 CROSS SECTION NO. 4 MILE 6.90 390 385 380 375 370 0 CROSS SECTION NO.5 MILE 8.85 390 385 380 375 370 CROSS SECTION N0.6 BUENA CREEK (TRIB.) MILE 1.04 LEGEND Standard Project Flood. Intermediate Regional Flood. NOTES: 1. HORIZONTAL DISTANCE IN HUNDRED FEET 1. SECTIONS TAKEN LOOKING DOWNSTREAM 3- ADDITIONAL CROSS SECTIONS WERE TAKEN BUT NOT SHOWN AND ARE AVAILABLE AT THE DISTRICT OFFICE DEPARTMENT OF THE ARMY LOS ANGELES DISTRICT, CORPS OF ENGINEERS LOS ANGELES, CALIFORNIA FLOOD PLAIN INFORMATION SELECTED CROSS SECTIONS AGUA HEDIONDA CREEK SAN DIEGO COUNTY, CALIFORNIA JULY 1973 ""PLATE""" 16