HomeMy WebLinkAbout5656675; Buena Vista Creek - Pacific to Vista; Flood Plain Information; 1973-07-01FLOOD PLAIN INFORMATION
BUENA VISTA GREEK
PACIFIC OCEAN TO VISTA
SAN DIEGO COUNTY, CALIFORNIA
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BEST ORIGINAL BiST ORIGINAL * ££/
RECEIVED
FE3 0 i ;S95
LADWIG DESIGN GR
PREPARED FOR
SAN DIEGO COUNTY
BY THE
DEPARTMENT OF THE ARMY, LOS ANGELES DISTRICT, CORPS OF ENGINEERS
LOS ANGELES, CALIFORNIA
JULY 1973
I/
03Vi3338
83 H(!l23fl O
*-.
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 19
FIGURES
Figure
1 Atchison, Topeka and Santa Fe Railway Company bridge over
Buena Vista Lagoon (looking upstream) 6
2 Same bridge as in Figure 1 (looking downstream) .......... 6
3 Interstate 5 bridge over Buena Vista Lagoon (looking upstream) 7
4 Jefferson Street bridge (looking downstream). This point
marks the entrance to Buena Vista Lagoon 7
5 Haymar Drive bridge at river mile 2.27 (looking upstream) . ,. 8
6 El Camino Real bridge (looking downstream) 8
7 Haymar Drive bridge at river mile 2.75 (looking downstream) ........ 9
8 Thunder Drive bridge (looking upstream) .... .... . . ..... .'.^,^. > 9
9 Future flood heights at Buena Vista Pumping Station at ,.;
Jefferson Street and Buena Vista Creek .".. ... . . ~.'.'.'."-;"." W:.". . . 21
10 Future flood heights at Sewage Treatment Plant 22
11 Future flood heights at Lawson Poofs, City of Oceanside . . . .-::-./. ... 23
12 Future flood heights at downstream side of College Boulevard ....... 24
13 Future flood heights at Exxon Service Station at Melrose Drive
at Haciendia Drive 25
PLATES
Plate
1 General Map Opposite Preface
2 Index — Flooded Area Follows Text
3-6 Flooded Areas At end of report
7-10 High Water Profiles At end of report
11 Selected Cross Sections At end of report
COVER PHOTOGRAPH
Buena Vista Lagoon looking upstream from Hill Street.
CONTENTS
Page
PREFACE i
BACKGROUND INFORMATION 1
Settlement 1
The Stream and Its Valley 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 Their Impact 5
Obstructions to floodflows 5
Flood damage reduction measures 10
Other factors and their impacts 10
Flood warning and forecasting 10
Flood fighting and emergency evacuation plans 10
Floatable material stored in 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 .^^^. ,..,,^ .,r^ . i.^v,iu._7"; . . .... ; . vdj. . . .\ 14
Frequency ...... ^ .7. . . *__. .". . •. ^r-;:^; t , . ."•.< .'"7V; . . / :^. . . .-"-. . . . . . "15v-.ir ^ , ' - -^;J---:-j^-.rr:-.-_ ... - ;-^; =r,- - ^-.. --^--..,-..,^.^^^^0!?^.^^^ ; -. -----Hazardsof Large Floods . . . .••:-. .rr::^.'-;;: .-;'... . rv .-1.1 . . ... ..... 15
Flooded areas and flood damages . .•. .......!... . 16
. ;..;;•'Obstructions . v ". . . . . ., 17
Velocities of flow V .......':.. ". . J.l 17
Rates of rise and duration of flooding . . " 19
Photographs, future flood heights 20
GLOSSARY 26
PREFACE
The portion of the cities of Carlsbad, Qceanside and Vista and of San Diego County covered by this
report is subject to flooding from Buena Vista 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 underpressure 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 flood proofing, 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.
A t 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.
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BACKGROUND INFORMATION
Settlement
Most of the flood plains in the reach of Buena Vista Creek studied lies within the
incorporated cities of Carlsbad, Oceanside and Vista. Only a very small part (mile 5.53 to
mile 5.68) lies within the unincorporated San Diego County area. 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 never did lead to
self-sufficiency; so crop-raising and other agricultural uses gradually replaced it as the
significant land use. The self-sufficiency of agriculture, mixed with fight ranching, had
already been demonstrated at the various missions established in the San Diego area. With
some exceptions, the land use continues to be agricultural today, because water is readily
available and there is arable land just outside the flood plain. However, pressure from
developers could result in increased residential use in the near future; the population in the
Carlsbad-Oceanside-Vista area is expected to increase rapidly by 1980.
The Stream and Its Valley
The Buena Vista Creek watershed is located in the northwest portion of San Diego
County, California, about 33 air miles north of the City of San Diego and 9 miles east of
Oceanside. Buena Vista Creek drains an area of 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 of
1,671 feet (mean sea level) in the San Marcos Mountains 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
Greek Bl'siri; on the northeast by San Marcos Mountains; and on the west by the Pacific
"Ocean, •Bueria Vista Creek originates in the San Marcos Mountains."Runoff from several
tributaries quickly converge into one main improved channel within the City of Vista. Flow
is generally in a southwest direction through the City of Vista. As it leaves the City of'Vista,
flow becomes more westward and slopes become more gentle, discharging into Buena Vista
Lagoon about 3 miles downstream. Streamflow eventually enters the Pacific Ocean some
2-1/2 miles farther downstream after being temporarily delayed by the considerable storage
in the lagoon. The stream gradients range from 68 feet per mile in the upper reaches to 32
feet per mile in the lower reaches of the basin. The average gradient within the reach studied
is 39 feet per mile.
Buena. Vista Creek is joined by several tributaries within a mile or two downstream from
its origin in the San Marcos Mountains. About one-half mile farther downstream Buena
Vista Creek becomes an improved channel and continues in an improved condition to just
downstream of Hacienda Drive at mile 7.03. Downstream from here, it is a natural channel
of narrow width and fairly wide overbanks averaging about 400 to 500 feet in width before
entering an improved channel about one-half mile upstream of El Camino Real. Flow
continues in the improved channel to discharge into Buena Vista Lagoon at Jefferson
Street crossing. Buena Vista Lagoon has considerable storage capacity which accounts for
much smaller peak outlet flows from the lagoon into the Pacific Ocean, the downstream
limit of this study.
Throughout the study reach, with the exception of the first quarter-mile upstream of the
State Highway 78 bridge, Buena Vista Creek parallels State Highway 78 as it flows westward
to the ocean. Between mile 1.0 and mile 3.0 State Highway 78 acts as a levee on the north
side of the channel.
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 at several points
along Buena Vista Creek are shown in table 1.
TABLE 1
DRAINAGE AREAS
• Ta2&fi2r *^w* * ^-^""'
Location on Buena Vista Creek
At entrance to Lagoon
Downstream of confluence with unnamed wash,
0.6 miles upstream of El Camino Real
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'Sunset-Drive
At Melrose Drive
Drainage Area
Square Miles
18.8
14.2
- 12.3 ~
8.7,
" Natural vegetation is abundant on the flood plains. It consists 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 three industrial developments and scattered private farms and ranches, there is
virtually no development on the flood plains of Buena Vista Creek. There is some heavy
residential development concentrated around the Buena Vista Lagoon area. There is also
some residential and commercial development on the north side of State Highway 78 which
parallels the channel. This development is increasing steadily, many homes and businesses
having been developed within the last five years. There are also many commercial
developments and department stores around Plaza Camino Real (see pi..4). However, all
these existing developments and others presently under construction are located outside of
the flood plain. The three industrial developments on the flood plain are:
a. A sewage treatment pumping plant between the channel and State Highway 78 at
approximately mile 2.1. This plant was recently completed and pumps sewage to the
Carlsbad Sewage Treatment Plant located elsewhere in the City of Carlsbad;
b. A rock excavation operation, "H. G. Fenton Materials Company", involves rock
excavation, mining and crushing.
c. The "South Coast Asphalt Plant" which has a hot-asphalt-surfacing mixing plant as
well as a ready mix concrete plant. Both "H. G. Fenton Materials" and the "South Coast
Asphalt Plant" are located around mile 4.2 just downstream of the College Boulevard
crossing.
Small farms located just outside the flood plain produce avocados, oranges, lemons,
tomatoes and winter vegetables. Ranching is confined to light grazing of cows and horses.
Only about five percent of the approximately 600 acres in the flood plains in this study can
be considered as developed.
State Highway 78, abuts the creek for almost the entire study reach. It connects with
Interstate Highway 5 on the west and U.S. Highway 395 on the east facilitating quick
transportation and communication between the various cities of Oceanside, Carlsbad and
Vista; to the towns of San Marcos and Escondido and to communities outside the
immediate area. Several highway interchanges have recently been constructed, such as at
Jefferson Street (see pi. 3} and College Boulevard which traverse the flood plain. The
provision of these excellent transportation facilities will definitely contribute to increased
residentraf, commercial and industrial development in the area.
The environmental attributes of Buena Vista Lagoon are clearly visible to any visitor to
the area. It provides breeding habitat for a variety of mammals and birds, including mallard
ducks and light-footed clapper rails, an endangered species. In addition, these wetlands are
extremely important to migratory waterfowl and shore birds for resting and feeding.
A weir was constructed in an outlet channel to the ocean by the Buena Vista Lagoon
Property Owners Association. This weir serves to maintain the water surface elevation in the
lagoon to about 6 feet above mean sea level, providing a healthy supply of suitable water to
birds and mammals that inhabit the lagoon.
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*».ii
FLOOD SITUATION
Sources of Data and Records
Only one stream gage is located within the Buena Vista Creek watershed at Wildwood
Park (see pi. 1). However, because data from this gage is severely limited and because
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, data from several gages in nearby basins (see table 2}
were adjusted to the study area of Buena Vista Creek for hydrologic computations because
the physiographic and rreteorologic characteristics of these basins are similar to those of the
Buena Vista Creek basin.
TABLE 2
STREAM-GAGING STATIONS
Stream Gage _
Buena Vista Creek in ^
.Wildwood Park .7. ,, ,-, ^r,.-. v-
Los F lores Creek near Oceanside^ .--'•!•- ';.• ;i-.;
• i -, ; ,.- .. '
San Onofre Creek near San Onofre
De Luz Creek near Fallbrook
San Juan Creek near San
Juan Capistrano
Drainage Area Period of
(sq. miles) Record
106.00
Maximum Recorded
Peak Flow
C.F.S. Date
,4.29,
26.60
34.60
47.90
; :: 1963-1971,;,,
--' "• •'-*•'-'*
1952-1970 ;
1951-1967
1951-1969
162r^v.^.4. .. ,-,
"* "4,200 ,
2,680
7,800
Feb. 1969
1 ''g!r'
Feb! 1969
•T <Apr. 1958
Feb. 1970
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 Buena Vista Creek as well as in 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 Their 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 5, 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
floodplain.
r
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 hydraulic capacity
of obstructive bridges retards floodflows and results in flooding upstream, erosion around
bridge approach embankments, and possible damage to the overlying roadbed.
•^^^^^y;:^:^^^
m^^'^^f^^^^^^
Figure 1 — Atchison, Topeka and Santa Fe Railway Company bridge
over Buena Vista Lagoon (looking upstream).
Figure 2 — Same bridge as in Figure 1 {looking downstream),
Figure 3 - Interstate 5 bridge over Buena Vista Lagoon (looking
upstream).
Figure 4 — Jefferson Street bridge {looking downstream). This
point marks the entrance to Buena Vista Lagoon.
Figure 5 - Haymar Drive bridge at river mile 2.27 (looking
upstream).
Figure 6 - El Camino Real bridge (looking downstream).
Figure 7 - Haymar Drive bridge at river mile 2.75 (looking
downstream).
Figure 8 - Thunder Drive bridge (looking upstream).
Flood damage reduction measures - There are no Federal flood control projects in the
study reach and none is contemplated in the foreseeable future. A graded earth channel
about 3/4 mile long was constructed between Jefferson Street and El Camino Real. It is
maintained by several private interests in the area. This channel would protect the adjacent
property from inundation during low flows but is not nearly adequate to contain large
floodflows such as the Intermediate Regional or Standard Project Floods.
There is also about 1/4 mile of concrete-lined channel from just downstream of El
Camino Real to the Haymar Drive bridge at mile 2.75. Rip rap also protects the channel
banks and bridge abutments for about 300 feet upstream of Haymar Drive bridge. The
concrete channel and slope protection were installed and are maintained by the California
Division of Highways. The California Division of Highways also maintains about 3/4 mile of
improved earth channel between mile 7.0 and the upstream limit of study. None of these
channels have the capacity to entirely contain the Intermediate Regional or Standard
Project Floods.
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 specfffc flood "forecasts are hot made for the Buena Vista Creek drainage basin,
daily weather forecasts applicable to the area are issued by the National Weather Seryice
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
i 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 in the flood plain - No unrestrained floatable objects such as
empty tanks or piles of lumber are known to be on the flood plains of Buena Vista Creek.
This is mainly because the scattered private farms and ranches on the flood plains do not
result in the accumulation of significant amounts of floatable materials that could be carried
away by f loodwaters.
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11
PAST FLOODS
Summary of Historical Floods
Damaging floods have occurred in the region which includes the study basin in 1862,
1884, 1895, 1916, 1927, 1932, 1938 and 1942. Little information is available, but
indications are that significant inundation occurred in the basin, blocking roads and flooding
out farmhouses and crops. 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
Nine years of record are available from the stream gage at Wildwood Park but no major
floods have been recorded at this gage within such a short period of time. Information on
historical floods 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 area.
Flood Descriptions
Very few descriptions of past floods that have directly affected the study area are
available and no photographs were found of flood damage in the Buena Vista drainage area.
However, the following excerpts from several newspapers in the area regarding past storms
should serve to depict the type of flood damage which has occurred in the area.
EXCERPT EROM THE OCEANSIDE BLADE, JANUARY
1 weeR"Sah Diego County has been struggling in the grip of a storrrPahd ffoods;'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 Bonsall. 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."
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."
12
"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."
till
13
FUTURE FLOODS
Although floods of the same magnitude as those that have occurred in the past could
i 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
:$$P| Standard Project Flood would be larger and would occur less frequently than the
§f#$|| 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, runofl.characteris.tics.p.f; the stream basjq^S|nce, there,, are. very, limited^
.streamflow, records=,fo.r_tihe.stucly.reach, it was necessary to^anajyze^recipitation _and
streamflow records of other stream" basins having -hydrologic, meteorologic, and
physiographic characteristics similar to those of the Buena Vista Creek basin. Studies were
made to transpose the information thus derived to the study basin and to compute fteak
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 2.
In addition to the data from the Wildwood Park stream gage, stream gaging stations for
Los Flores Creek, San Onofre Creek, De Luz Creek and San Juan Creek yielded data for
transposition to the study basin.
Standard Project Flood
For the purpose of determining peak flows of the Standard Project Flood, a standard
project storm 1 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.
1/ The most severe combination of meterologic conditions reasonably characteristic of the
geographic region, excluding extremely rare combinations.
14
TABLE 3
PEAK FLOWS FOR INTERMEDIATE REGIONAL
AND STANDARD PROJECT FLOODS
Location
At entrance to lagoon
Upstream from
El Camtno Real
At Sunset Drive
At Melrose Drive
Miles
Up-stream
from Mouth
1.6
2.5
5.5
7.3
Drainage
Area
(sq. mi.)
18.8
14.2
12.3
8.7
Intermediate Standard
Regional Flood Project Flood
(cfs)
7,800
7,200
6,900
(cfs)
11,200
9,900
10,300
9,900
*Decrease in discharge between Sunset Drive and El Camino Real due to significant reduction
in percent imperviousness.
Frequency
Because official records of past floods in the basin do not exist, the assignment of
frequencies to those 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 isee-Glossary for definition) are
_possible*.Statistical frequencies of occurrence cannot be assigned to floods-of ;he 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 property would also occur.
However, flood damage to residences would be small since most residential development has
occurred outside of the flood plain.
ill
15
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
ijjjjfc ultimately submerged. Decaying flood-deposited garbage or other organic materials could
create hazards in terms of medical, fire, or law enforcement emergencies.
Flooded areas and flood damages - The areas along Buena Vista Creek that would be
flooded by a Standard Project Flood are shown on plate 2, which is an index map to plates
3 through 6. Areas that would be flooded by the Intermediate Regional and Standard
Project Floods are shown in detail on plates 3 through 6. These areas include agricultural
and residential sections and the associated streets, roads, and public utilities in the flood
plains of these streams. Two isolated industrial areas are also included. 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 7 through 10 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 11. Specific damage that would be expected at
various locations are listed below:
'"'"'"''a. ''Damage to"State Highway- 7Etinthe vicinity:'of Buena Vista Lagoon (mile 1.3) due to
^inundation ofthe highway up to deptrTs oT2 feet for the IntermedTate^Regional Flood and 5
feet for the Standard Project Flood. Such inundation could cause interruption of traffic,
traffic delays or inconvenience to some communities during these very large floods. No such
problem would exist, however, for floods of recurrence interval less than 100 years.
b. There would be areas of heavy ponding on the flood plains immediately upstream of
Jefferson Street. The Buena Vista Pumping Station would be damaged and significant
amounts of silt and debris would accumulate on the site.
c. A few commercial developments between State Highway 78 and the channel, would
be damaged by inundation to depths of about 6 feet for the Standard Project Flood.
d. Several local roads and streets on the flood plains near mile 5.0 would be inundated
and partially washed out.
e. Small private earth reservoirs around mile 6.0 would be destroyed.
f. Several farms in the upper reaches of Buena Vista Creek would be inundated and
cropland washed away.
'
16
g. Most small culverts and minor road crossings would be washed out.
Limits of overflow indicated on plates 3 through 6 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 Buena Vista Creek. These include one
Atchison Topeka and Santa Fe Railroad bridge (mile 0.21), one Interstate Freeway bridge at
mile 0.92 (Interstate 5), several major road bridges and several smaller bridges and culverts.
All of these bridges and culverts are shown on the profile plates (plates 7 to 10}.
Photographs of the major bridges and culverts are shown on figures 1 through 8. A listing of
most of these structures is shown in table 4 with water surface elevations for the
Intermediate Regional and Standard Project Floods.
The railroad bridge. Interstate 5 Highway bridge, Jefferson Street bridge and E! Camino
Real bridge all have the capacity to pass either the Intermediate Regional Flood or Standard
Project Flood. The Haymar Drive bridge can safely pass the Intermediate Regional Flood
but will be overtopped by the Standard Project Flood. All the other bridges and culverts do
not have the capacity to pass either the Intermediate Regional or Standard Project Flood
without being overtopped. Most of these inadequate bridges would be inundated to depths
of about 4 feet (see profile plates) for the Standard Project Flood and would be severely
damaged.
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 flood waters
•in Agua -Hedionda Lagoon and due to the relatively large width of flow, the velocity is very
low through the lagoon averaging about 1 foot per second for the Intermediate Regional
Flood and about 1.5 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 stream banks and transporting large rocks.
17
tiifl
TABLE 4
BRIDGES WITHIN STUDY AREA
Elevation (b)
Low
Identification
Buena Vista Creek:
Atchison Topeka & Santa Fe
Railroad Bridge
Interstate 5 bridge
Jefferson Street Bridge.
Haymar Drive Bridge ..'
ElCamino Real Bridge
Haymar Drive !^
(Extension) Bridge
College Boulevard :igV
*rii-Qld Thunder Dr. Bridge ?:^::;
Thunder Dr. Bridge . .
Sunset Drive Bridge "
Hacienda Dr. Extension
.Breeze Hill Drive
Frontage Road
Melrose Drive
State Highway 78
(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 basin on estimated flow and existing channel and
structures.
Intermediate Regional Flood **Standard Project Flood
.ocation
(a)
0.21
0.92
1.57
2.27
2.39
2.74
4.47,
'iSeC
4.98. H
5-52 !!
6.56 ' ;
6.99
7.03
7.32
7.53
Streambed
0.0
0.0
4.5
10.3
12.4
22.6
152.5 -
;I^7K
; I77-6. .
196.3
262.6~
279.3
281.1
291.1
294.7
Chord
(c)
13.5
22.0
20.3
22.0
34.0
33.0
160.5
;J78.4:-
184.6
212,0
270.6
289.1
289.4
299.4
303.0
Roadway
(d)
16.0
24.0
24.0
25.0
37.0
36.0
164.3
180.0U,
191.0
214.8
271.6
291.3
292.6
304.0
307.1
IRF*
(e)
8.2
12.7
15.5
23.7
25.0
34.0
167.1
184.3
192.9
216.8
277.1
293.2
295.5
304.7
311.3
SPF**
(e)
9.3
16.0
18.0
24.2
28.5
37.0
168.3
..-186.8
195.]
217.9
278.8
294.1
296.9
306.3
315.3
18
TABLE 5
VELOCITY OF FLOW
Stream and Location
Buena Vista Creek:
Upstream of El Camino Real
Upstream of College Blvd.
Upstream of Sunset Dr.
Miles Intermediate Standard
Upstream Regional Flood Project Flood
From Channel Overbank Channel Overbank
Mouth fps fps fps fps
3.45
4.75
6.33 12
10
13
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, Buena Vista 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 at the Melrose Drive Bridge, 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).
TABLE 6
RATES OF RISE AND DURATION
(at Pacific Coast Highway)
Flood
Intermediate Regional
Standard Project
Height
of Rise
(Feet)
5.0
6.5
Time
of Rise
(Hours)
0.5
0.8
Duration of
Flood Stage
(Hours)
0.7
1.1
As Table 6 indicates the flood waters reach maximum floodflow level in only one-half
hour after flood stage is reached for the Intermediate Regional Flood, and also in less than
one hour for the Standard Project Flood.
19
On the average, the water surface elevation of the Standard Project Flood on Buena Vista
Creek would be about one and one-half feet higher than that of the Intermediate Regional
Flood, except in the lagoon area between Interstate 5 Hwy and Jefferson Street Bridge
where the Standard Project Flood averages about 3 feet higher than 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 Buena Vista Creek
flood plain, are indicated on the following photographs, (figures 9 to 13J.
20
Figure 9 — Future flood heights at Buena Vista Pumping Station
at Jefferson Street and Buena Vista Creek (see magnified view
above).
21
STANDARD
PROJECT FLOOD
f
INTERMEDIATE
REGIONAL ROOD-*1«
ill
Figure 10 — Future flood freights at Sewage
Treatment Plant (0.3 mile downstream of El Camino
Real).
22
STANDARD PROJECT FLOOD -+L
(NTE*M£DIATf REGIONAL FLOOD -*fml'
Figure 12 - Future flood heights at downstream side of College
Boulevard (looking north).
24
STANDARD PROJECT HOODCHH !••• IlliM
^INTERMEDIATE REGIONAL FLOOD
STANDARD PROJECT FLOOD
REGJONAl Ft
Figure 11 - Future flood heights at Lawson Pools, City of
Oceanside (on right bank 0.15 mile downstream of El Camino
Real). {See magnified view above.)
23
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
groundwater coincident with increased streamsflow, 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 Plains — 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 floodwater.
: Flood Profile — A graph showing the relationship of watersurfaceelevation 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.
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 occuring in the months of
December through March, characterized by heavy and prolonged rainfall over a large area.
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.
26
•; -tl,-" -,' •
STANDARD PROJECT flOOD
INTERMEDIATE REGIONAL FLOOD-**.,
t r'
STANDARD PROJECT WOOD
RMED7ATE" REG/ONAt FLOOD
Figure 13 - Future flood heights at Exxon Service Station at
Melrose Drive at Hacienda Drive (Just south of Hwy78), City of
Vista (see magnified view above).
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 Flood — 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.
27