Section 8: Flood

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Why are Floods a Threat to the City of West Covina?

The City of West Covina is bisected by the Walnut Creek Wash. Prior to the building of this flood control project, areas of farmland that were later to become West Covina, would flood during heavy rainstorms. Flooding poses a threat to life and safety, and can cause severe damage to public and private property. The City of West Covina has a number of dry creeks that cut across the landscape and flow into flood control channels. Living within the arid climate of Southern California it easy to overlook the damage that may be caused by flooding as these channels fill with rain runoff.

The City of West Covina most recently experienced damage resulting from the rainstorms and flooding that occurred throughout Southern California from February 10 - 15, 1992. A Presidential Declaration assisted the City with its recovery. Federal funds were received to assist the whole City and particularly the area of Azusa Avenue and Amar Road. The businesses and apartments in this area were adversely impacted with damage to structures, property/inventory, and loss of business.

The City of West Covina was also adversely impacted by the rainstorms of February 1978. During this time, the City of West Covina received federal disaster funds through Declaration FDAA 547 DR in the amount of $308,584. Damage from these storms included a road washout, slope failure at water reservoir #2, and the subsidence of fuel tanks at the Police Department facility.

Areas effected by this storm flooding were minimized by previous mitigation projects. Prior to the flood control system being built, Walnut Creek, which flows across the central section of the City from east to west, would overflow its banks and damage agricultural land. The construction of the San Gabriel Dam No. 2 in 1933, and the storm drain system and channel into the San Gabriel and Rio Hondo rivers in 1938, helped mitigate flooding. Additionally the construction of nearby Puddingstone Dam and San Dimas Canyon Dam in 1921 aided in the mitigation of flooding.

History of Flooding in The City of West Covina

The City of West Covina is susceptible to flooding primary from rainstorm flooding.

According to the records on Flood Insurance claims kept by the FEMA National Flood Insurance Program (NFIP) there have been no claims filed in the City of West Covina for the period covering January 1, 1978 to December 31, 2003. These statistics would only show any claims made by West Covina Property owners with FEMA NFIP flood insurance. As of records current to December 31, 2003, there are only 4 properties in West Covina insured under this program with a total of $ 1,605,000.00 insurance in-force and a total of $ 10,607.00 written premium in-force.

There are a number of rivers in the Southern California region, but the river with the best recorded history is the Los Angeles River. The flood history of the Los Angeles River is generally indicative of the flood history of much of Southern California.

Historic Flooding in Los Angeles County

Records show that since 1811, the Los Angeles River has flooded 30 times, on average once every 6.1 years. But averages are deceiving, for the Los Angeles basin goes through periods of drought and then periods of above average rainfall. Between 1889 and 1891 the river flooded every year, and from 1941 to 1945, the river flooded 5 times. Conversely, from 1896 to 1914, a period of 18 years, and again from 1944 to 1969, a period of 25 years, the river did not have any serious floods.

Table 8 -1 Major Floods of the Los Angeles River

Major Floods of the Los Angeles River
Sources: and

While the City of West Covina is 18.5 miles east of downtown Los Angeles, it is not so far away as to not be affected by the same heavy rains that brought flooding to Los Angeles. The close proximity and similar geography of the San Fernando Valley, Los Angeles Basin, San Gabriel Valley and Pomona Valley make each of these areas susceptible to the same weather pattern and runoff from elevated areas to the flats. The towering mountains that give the Los Angeles region its spectacular views also wring a great deal of rain out of the storm clouds that pass through. Because these mountains are so steep, the rainwater moves rapidly down the slopes and across the coastal plains on its way to the ocean.

"The Santa Monica, Santa Susana and Verdugo mountains, which surround three sides of the valley seldom reach heights above three thousand feet. The western San Gabriel Mountains, in contrast, have elevations of more than seven thousand feet. These higher ridges often trap eastern-moving winter storms. Although downtown Los Angeles averages just fifteen inches of rain a year, some mountain peaks in the San Gabriels receive more than forty inches of precipitation annually"
Naturally, this rainfall moves rapidly down stream, often with severe consequences for anything in its path. In extreme cases, flood-generated debris flows will roar down a canyon at speeds near 40 miles per hour with a wall of mud, debris and water tens of feet high.

In Southern California, stories of floods, debris flows, persons buried alive under tons of mud and rock and persons swept away to their death in a river flowing at thirty-five miles an hour are without end. No catalog of chaos could contain all the losses suffered by man and his possessions from the regions rivers and streams.

What Factors Create Flood Risk?

Flooding occurs when climate, geology, and hydrology combine to create conditions where water flows outside of its usual course. In the City of West Covina, geography and climate combine to create intermittent seasonal flooding conditions.

Winter Rainfall

Over the last 125 years, the average annual rainfall in Los Angeles is 14.9 inches. But the term "average" means very little as the annual rainfall during this time period has ranged from only 4.35 inches in 2001-2002 to 38.2 inches in 1883-1884. In fact, in only fifteen of the past 125 years, has the annual rainfall been within plus or minus 10% of the 14.9-inch average. And in only 38 years has the annual rainfall been within plus or minus 20% of the 14.9-inch average. This makes the Los Angeles basin a land of extremes in terms of annual precipitation.

The City of West Covina is in the San Gabriel Valley, the eastern section of the Los Angeles County. It is up against the San Jose Hills, which increases the collection of rainwater.


Another relatively regular source for heavy rainfall, particularly in the mountains and adjoining cities is from summer tropical storms. Table 8-1 lists tropical storms that have had significant rainfall in the past century, and the general areas affected by these storms. These tropical storms usually coincide with El Nino years.

Table 8-2 Tropical Cyclones affecting Southern California


Geography and Geology

The greater Los Angeles Basin is the product of rainstorms and erosion for millennia. "Most of the mountains that ring the valleys and coastal plain are deeply fractured faults and, as they (the mountains) grew taller, their brittle slopes were continually eroded. Rivers and streams carried boulders, rocks, gravel, sand, and silt down these slopes to the valleys and coastal plain....In places these sediments are as much as twenty thousand feet thick"

Much of the coastal plain rests on the ancient rock debris and sediment washed down from the mountains. This sediment can act as a sponge, absorbing vast quantities of rain in those years when heavy rains follow a dry period. But like a sponge that is near saturation, the same soil fills up rapidly when a heavy rain follows a period of relatively wet weather. So even in some years of heavy rain, flooding is minimal because the ground is relatively dry. The same amount of rain following a wet period of time can cause extensive flooding.

The greater Los Angeles basin is for all intents and purposes built out. This leaves precious little open land to absorb rainfall. This lack of open ground forces water to remain on the surface and rapidly accumulate. If it were not for the massive flood control system with its concrete lined river and stream beds, flooding would be a much more common occurrence. And the tendency is towards even less and less open land. In-fill building is becoming a much more common practice in many areas. Developers tear down an older home which typically covers up to 40% of the lot size and replacing it with three or four town homes or apartments, which may cover 90-95% of the lot.

Another potential source of flooding is "asphalt creep." The street space between the curbs of a street is a part of the flood control system. Water leaves property and accumulates in the streets, where it is directed towards the underground portion of the flood control system. The carrying capacity of the street is determined by the width of the street and the height of the curbs along the street. Often, when streets are being resurfaced, a one to two inch layer of asphalt is laid down over the existing asphalt. This added layer of asphalt subtracts from the rated capacity of the street to carry water. Thus the original engineered capacity of the entire storm drain system is marginally reduced over time. Subsequent re-paving of the street will further reduce the engineered capacity even more.

Flood Terminology

A floodplain is a land area adjacent to a river, stream, lake, estuary, or other water body that is subject to flooding. This area, if left undisturbed, acts to store excess floodwater. The floodplain is made up of two sections: the floodway and the flood fringe.

100-Year Flood
The 100-year flooding event is the flood having a one percent chance of being equaled or exceeded in magnitude in any given year. Contrary to popular belief, it is not a flood occurring once every 100 years. The 100-year floodplain is the area adjoining a river, stream, or watercourse covered by water in the event of a 100-year flood. Map 7 illustrates the 100-year floodplain in the City of West Covina.

The floodway is one of two main sections that make up the floodplain. Floodways are defined for regulatory purposes. Unlike floodplains, floodways do not reflect a recognizable geologic feature. For NFIP purposes, floodways are defined as the channel of a river or stream, and the overbank areas adjacent to the channel. The floodway carries the bulk of the floodwater downstream and is usually the area where water velocities and forces are the greatest. NFIP regulations require that the floodway be kept open and free from development or other structures that would obstruct or divert flood flows onto other properties.

The City of West Covina regulations prohibit all development in the floodway. The NFIP floodway definition is "the channel of a river or other watercourse and adjacent land areas that must be reserved in order to discharge the base flood without cumulatively increasing the water surface elevation more than one foot. Floodways are not mapped for all rivers and streams but are generally mapped in developed areas.


Flood Fringe

The flood fringe refers to the outer portions of the floodplain, beginning at the edge of the floodway and continuing outward. For the City of West Covina the flood fringe is defined as "the land area, which is outside of the stream flood way, but is subject to periodic inundation by regular flooding." This is the area where development is most likely to occur, and where precautions to protect life and property need to be taken.


For floodplain ordinance purposes, development is broadly defined by the City of West Covina Zoning Ordinance to mean "any manmade change to improved or unimproved real estate, including but not limited to buildings or other structures, mining, dredging, filling, grading, paving, excavation, or drilling operations located within the area of special flood hazard." The definition of development for floodplain purposes is generally broader and includes more activities than the definition of development used in other sections of local land use ordinances.

Base Flood Elevation (BFE)

The term "Base Flood Elevation" refers to the elevation (normally measured in feet above sea level) that the base flood is expected to reach. Base flood elevations can be set at levels other than the 100-year flood. Some communities choose to use higher frequency flood events as their base flood elevation for certain activities, while using lower frequency events for others. For example, for the purpose of storm water management, a 25-year flood event might serve as the base flood elevation; while the 500-year flood event may serve as base flood elevation for the tie down of mobile homes. The regulations of the NFIP focus on development in the 100-year floodplain.

Characteristics of Flooding

Storm water flooding is the primarily flooding to affect the City of West Covina as natural and man-made channels fill with water, riverine flooding or urban flooding occurs when there is more water to carry than what the channel can handle. In addition, any low-lying area has the potential to flood. The flooding of developed areas may occur when the amount of water generated from rainfall and runoff exceeds a storm water system's capability to remove it.

Riverine Flooding

Riverine flooding is the overbank flooding of rivers and streams. The natural processes of riverine flooding add sediment and nutrients to fertile floodplain areas. Flooding in large river systems typically results from large-scale weather systems that generate prolonged rainfall over a wide geographic area, causing flooding in hundreds of smaller streams, which then drain into the major rivers.

Shallow area flooding is a special type of riverine flooding. FEMA defines shallow flood hazards as areas that are inundated by the 100-year flood with flood depths of only one to three feet. These areas are generally flooded by low velocity sheet flows of water.

Urban Flooding

As land is converted from fields or woodlands to roads and parking lots, it loses its ability to absorb rainfall. Urbanization of a watershed changes the hydrologic systems of the basin. Heavy rainfall collects and flows faster on impervious concrete and asphalt surfaces. The water moves from the clouds, to the ground, and into streams at a much faster rate in urban areas. Adding these elements to the hydrological systems can result in floodwaters that rise very rapidly and peak with violent force.

Each year a greater percentage of the area in the City of West Covina is developed as land with a high concentration of impermeable surfaces that either collect water, or concentrate the flow of water in unnatural channels. During periods of urban flooding, streets can become swift moving rivers and basements can fill with water. Storm drains often back up with vegetative debris causing additional, localized flooding.

Dam Failure Flooding

Loss of life and damage to structures, roads, and utilities may result from a dam failure. Economic losses can also result from a lowered tax base and lack of utility profits. These effects would certainly accompany the failure of one of the major dams which protect the City of West Covina. The City of West Covina would be subject to inundation flooding if any of the following three dams were to fail, San Dimas Dam, Puddingstone Dam at Bonelli Park, or Santa Fe Dam.

Although the Santa Fe Dam is the nearest to the city of West Covina, it is a dry dam, it is utilized to control heavy runoff and to support ground water maintenance with its numerous settling basins. The Santa Fe Dam is controlled by the Army Corps of Engineers and is located in the City of Irwindale. The Santa Fe Dam is an earth-filled dam; the dam's construction was started in 1941 and completed in 1949. Construction was delayed during World War II. Santa Fe Dam would be the downstream control if there were to be any problems with the Morris or San Gabriel Dam in Azusa Canyon. Any overflow from failure of these dams is projected to spill out into the San Gabriel River wash and the secondary control area to the west of the 210 / 605 Freeway interchange. Downstream areas of inundation from this type of event are not projected to impact the City of West Covina, but will impact the City of Baldwin Park to the west.

Puddingstone Dam is managed by the Los Angeles County Public Works Department and is located in the Frank G. Bonelli County Park in the City of San Dimas. The Puddingstone Dam is an earth-filled dam built in 1928, with a rated capacity of 17,190 acre-feet of water (AFOW). Because of the recreational use of the area, a contract with Los Angeles County Parks and Recreation limits the capacity to 6,083 AFOW. Water flowing from this dam fills Walnut Creek and this watershed transects the City of West Covina as the Walnut Creek Wash.

The San Dimas Dam is managed by the Los Angeles County Public Works Department and is located in the Angeles National Forest in San Dimas Canyon, north of the cities of San Dimas and La Verne. The San Dimas Dam is a reinforced concrete dam built in 1922, with a rated capacity of 1,496 AFOW Water flowing from this dam fills San Dimas Creek which eventually flows into the San Dimas Wash and meets up with the Big Dalton Wash in the City of Irwindale. The Big Dalton Wash crosses the City of West Covina in the most northwest corner, at Azusa Canyon Road and San Bernardino Road.

The Walnut Creek spreading basin is controlled by the Los Angeles County Flood Control District and is located in the City of Covina on the West Covina - Covina city line. The spreading basin is just north of Garvey Ave North and west of Grand Avenue. The spreading basin is fed by the Walnut Creek Wash and any overage should flow down the storm channel from this location. Flooding from this water source might only be possible if the body of water is disturbed by shaking due to an earthquake, or if any water was displaced by a landslide into the basin. This is a natural basin and there is no dam holding back the water.

There is one open reservoir in the City of West Covina that is utilized for landscape irrigation at South Hills Country Club. This reservoir is not considered a dam because it sits in a natural bowl. The reservoir is fed by pipeline from Suburban Water Company and minimal slope runoff. The natural reservoir holds over 10,000 gallons of water and is located between Crescent View Drive, Sandy Hill Drive, and Golden Vista Drive .The reservoir is referred to by local citizens as "Lake West Covina".

Figure 8-1 Photo of reservoir for South Hills Country Club

Because dam failure can have severe consequences, FEMA requires that all dam owners develop Emergency Action Plans (EAP) for warning, evacuation, and post-flood actions. Although there may be coordination with county officials in the development of the EAP, the responsibility for developing potential flood inundation maps and facilitation of emergency response is the responsibility of the dam owner. For more detailed information regarding dam failure flooding, and potential flood inundation zones for a particular dam in the county, refer to the City of West Covina Emergency Action Plan.

There have been a total of 45 dam failures in California, since the 19th century. The significant dam failures in Southern California are listed in Table 8-3.

Table 8-3 Dam Failures in Southern California


The two most significant dam failures are the St. Francis Dam in 1928 and the Baldwin Hills Dam in 1963.

"The failure of the St. Francis Dam, and the resulting loss of over 500 lives in the path of a roaring wall of water, was a scandal that resulted in the almost complete destruction of the reputation of its builder, William Mulholland.

Mulholland was an immigrant from Ireland who rose up through the ranks of the city's water department to the position of chief engineer. It was he who proposed, designed, and supervised the construction of the Los Angeles Aqueduct, which brought water from the Owens Valley to the city. The St. Francis Dam, built in 1926, was 180 feet high and 600 feet long; it was located near Saugus in the San Francisquito Canyon.

The dam gave way on March 12, 1928, three minutes before midnight. Its waters swept through the Santa Clara Valley toward the Pacific Ocean, about 54 miles away. 65 miles of valley was devastated before the water finally made its way into the ocean between Oxnard and Ventura. At its peak the wall of water was said to be 78 feet high; by the time it hit Santa Paula, 42 miles south of the dam, the water was estimated to be 25 feet deep. Almost everything in its path was destroyed: livestock, structures, railways, bridges, and orchards. By the time it was over, parts of Ventura County lay under 70 feet of mud and debris. Over 500 people were killed and damage estimates topped $20 million."

The Baldwin Hills dam failed during the daylight hours, and was one of the first disaster events documented a live helicopter broadcast. "The Baldwin Hills Dam collapsed with the fury of a thousand cloudbursts, sending a 50-foot wall of water down Cloverdale Avenue and slamming into homes and cars on Dec. 14, 1963.

Five people were killed. Sixty-five hillside houses were ripped apart, and 210 homes and apartments were damaged. The flood swept northward in a V-shaped path roughly bounded by La Brea Avenue and Jefferson and La Cienega boulevards.

dam break
Beginning of the break in the dam.

The earthen dam that created a 19-acre reservoir to supply drinking water for West Los Angeles residents ruptured at 3:38 p.m. As a pencil-thin crack widened to a 75-foot gash, 292 million gallons surged out. It took 77 minutes for the lake to empty. But it took a generation for the neighborhood below to recover. And two decades passed before the Baldwin Hills ridge top was reborn.Figure 8-2 Baldwin Hills Dam - Dark spot in upper right hand quadrant shows the beginning of the break in the dam.

The cascade caused an unexpected ripple effect that is still being felt in Los Angeles and beyond. It foreshadowed the end of urban-area earthen dams as a major element of the Department of Water and Power's water storage system. It prompted a tightening of Division of Safety of Dams control over reservoirs throughout the state.

The live telecast of the collapse from a KTLA-TV helicopter is considered the precursor to airborne news coverage that is now routine everywhere."

12map8dam failures

Another flood related hazard that can affect certain parts of the Southern California region are debris flows. Most typically debris flows occur in mountain canyons and the foothills against the San Gabriel Mountains. However, any hilly or mountainous area with intense rainfall and the proper geologic conditions may experience one of these very sudden and devastating events.

"Debris flows, sometimes referred to as mudslides, mudflows, lahars, or debris avalanches, are common types of fast-moving landslides. These flows generally occur during periods of intense rainfall or rapid snowmelt. They usually start on steep hillsides as shallow landslides that liquefy and accelerate to speeds that are typically about 10 miles per hour, but can exceed 35 miles per hour. The consistency of debris flows ranges from watery mud to thick, rocky mud that can carry large items such as boulders, trees, and cars. Debris flows from many different sources can combine in channels, and their destructive power may be greatly increased. They continue flowing down hills and through channels, growing in volume with the addition of water, sand, mud, boulders, trees, and other materials. When the flows reach flatter ground, the debris spreads over a broad area, sometimes accumulating in thick deposits that can wreak havoc in developed areas."

What is the Effect of Development on Floods?

When structures or fill are placed in the floodway or floodplain water is displaced. Development raises the river levels by forcing the river to compensate for the flow space obstructed by the inserted structures and/or fill. When structures or materials are added to the floodway or floodplain and no fill is removed to compensate, serious problems can arise. Floodwaters may be forced away from historic floodplain areas. As a result, other existing floodplain areas may experience floodwaters that rise above historic levels. Local governments must require engineer certification to ensure that proposed developments will not adversely affect the flood carrying capacity of the Special Flood Hazard Area (SFHA). Displacement of only a few inches of water can mean the difference between no structural damage occurring in a given flood event, and the inundation of many homes, businesses, and other facilities. Careful attention should be given to development that occurs within the floodway to ensure that structures are prepared to withstand base flood events. In highly urbanized areas, increased paving can lead to an increase in volume and velocity of runoff after a rainfall event, exacerbating the potential flood hazards. Care should be taken in the development and implementation of storm water management systems to ensure that these runoff waters are dealt with effectively.

How are Flood-Prone Areas Identified?

Flood maps and Flood Insurance Studies (FIS) are often used to identify flood-prone areas. The NFIP was established in 1968 as a means of providing low-cost flood insurance to the nation's flood-prone communities. The NFIP also reduces flood losses through regulations that focus on building codes and sound floodplain management. In the City of West Covina, the NFIP and related building code regulations went into effect on March 1, 1978. NFIP regulations (44 Code of Federal Regulations (CFR) Chapter 1, Section 60, 3) require that all new construction in floodplains must be elevated at or above base flood level.

Flood Insurance Rate Maps (FIRM) and Flood Insurance Studies (FIS) Floodplain maps are the basis for implementing floodplain regulations and for delineating flood insurance purchase requirements. A Flood Insurance Rate Map (FIRM) is the official map produced by FEMA, which delineates SFHA in communities where NFIP regulations apply. FIRMs are also used by insurance agents and mortgage lenders to determine if flood insurance is required and what insurance rates should apply.

Water surface elevations are combined with topographic data to develop FIRMs. FIRMs illustrate areas that would be inundated during a 100-year flood, floodway areas, and elevations marking the 100-year-flood level. In some cases they also include base flood elevations (BFEs) and areas located within the 500-year floodplain. Flood Insurance Studies and FIRMs produced for the NFIP provide assessments of the probability of flooding at a given location. FEMA conducted many Flood Insurance Studies in the late 1970s and early 1980s. These studies and maps represent flood risk at the point in time when FEMA completed the studies. However, it is important to note that not all 100-year or 500-year floodplains have been mapped by FEMA.

FEMA flood maps are not entirely accurate. These studies and maps represent flood risk at the point in time when FEMA completed the studies, and does not incorporate planning for floodplain changes in the future due to new development. Although FEMA is considering changing that policy, it is optional for local communities. The City of West Covina is in the final process of confirming and adopting the latest additions to the FEMA FIRM map, adoption should be complete by 2005. Man-made and natural changes to the environment have changed the dynamics of storm water run-off in the future.

Flood Mapping Methods and Techniques

Although many communities rely exclusively on FIRMs to characterize the risk of flooding in their area, there are some flood-prone areas that are not mapped but remain susceptible to flooding. These areas include locations next to small creeks, local drainage areas, and areas susceptible to manmade flooding. Some storm flooding damage from past floods in the City of West Covina has been outside boundaries of the FEMA's FIRMs.

In order to address this lack of data some jurisdictions have taken efforts to develop more localized flood hazard maps. One method that has been employed includes using high-water marks from flood events or aerial photos, in conjunction with the FEMA maps, to better reflect the true flood risk. The use of GIS (Geographic Information System) is becoming an important tool for flood hazard mapping. FIRM maps can be imported directly into GIS, which allows for GIS analysis of flood hazard areas The City of West Covina is working with the FEMA to update FIRM maps and access the data for the City's GIS files as of this printing, no convertible files are available for West Covina.

Communities find it particularly useful to overlay flood hazard areas on tax assessment parcel maps. This allows a community to evaluate the flood hazard risk for a specific parcel during review of a development request. Coordination between FEMA and local planning jurisdictions is the key to making a strong connection with GIS technology for the purpose of flood hazard mapping.

FEMA and the Environmental Systems Research Institute (ESRI), a private company, have formed a partnership to provide multi-hazard maps and information to the public via the Internet. ESRI produces GIS software, including ArcViewC9 and ArcInfoC9 . The ESRI web site has information on GIS technology and downloadable maps. The hazards maps provided on the ESRI site are intended to assist communities in evaluating geographic information about natural hazards. Flood information for most communities is available on the ESRI web site. Visit for more information.

Hazard Assessment

Hazard Identification

Hazard identification is the first phase of flood-hazard assessment. Identification is the process of estimating: (1) the geographic extent of the floodplain (i.e., the area at risk from flooding); (2) the intensity of the flooding that can be expected in specific areas of the floodplain; and (3) the probability of occurrence of flood events. This process usually results in the creation of a floodplain map. Floodplain maps provide detailed information that can assist jurisdictions in making policies and land-use decisions.

Drainages in West Covina include the Holt Avenue spillway, Walnut Creek wash, Big Dalton wash, Vine Creek, drainage from BKK to Puente Creek, drainage at Nogales/Shakespeare, drainage at Eddes, drainage from Galster Park, Charter Oak Creek wash, drainage at Spring Meadow/Virginia drainage, Hidden Valley drainage. All are intermittent streams, none flow year round.

Most of West Covina is in FIRM Zone X - areas of 0.2% chance of flood.

Some areas adjacent to drainages and on the South Hills slopes are in FIRM Zone D - areas in which flood hazards are possible.

And then some areas downstream of drainages fall within FIRM Zone A - Special Flood Hazard Area (SFHA) subject to inundation by 1% annual chance of flood event, with no base elevations determined. Zone A areas include Vine Creek, drainage from Galster Park, drainage at Shakespeare/Nogales.

Data Sources

FEMA mapped the 100-year and 500-year floodplains through the Flood Insurance Study (FIS) in conjunction with the United States Army Corps of Engineers (USACE) in August of 1987. There were previous studies done, including a Housing and Urban Development (HUD) study, which mapped the floodplain in March of 1978, this is when the City of West Covina initially entered into the NFIP. The county has updated portions of the USACE and FEMA maps through smaller drainage studies in the county since that time.

Vulnerability Assessment

Vulnerability assessment is the second step of flood-hazard assessment. It combines the floodplain boundary, generated through hazard identification, with an inventory of the property within the floodplain. Understanding the population and property exposed to natural hazards will assist in reducing risk and preventing loss from future events. Because site-specific inventory data and inundation levels given for a particular flood event (10-year, 25-year, 50-year, 100-year, 500-year) are not readily available, calculating a community's vulnerability to flood events is not straightforward. The amount of property in the floodplain, as well as the type and value of structures on those properties, should be calculated to provide a working estimate for potential flood losses.

Risk Analysis

Risk analysis is the third and most advanced phase of a hazard assessment. It builds upon the hazard identification and vulnerability assessment. A flood risk analysis for the City of West Covina should include two components: (1) the life and value of property that may incur losses from a flood event (defined through the vulnerability assessment); and (2) the number and type of flood events expected to occur over time. Within the broad components of a risk analysis, it is possible to predict the severity of damage from a range of events. Flow velocity models can assist in predicting the amount of damage expected from different magnitudes of flood events. The data used to develop these models is based on hydrological analysis of landscape features. Changes in the landscape, often associated with human development, can alter the flow velocity and the severity of damage that can be expected from a flood event.

Using GIS technology and flow velocity models, it is possible to map the damage that can be expected from flood events over time. It is also possible to pinpoint the effects of certain flood events on individual properties. At the time of publication of this plan, data was insufficient to conduct a risk analysis for flood events in the City of West Covina. However, the current mapping projects will result in better data that will assist in understanding risk. This plan includes recommendations for building partnerships that will support the development of a flood risk analysis in the City of West Covina.

Community Flood Issues

What is Susceptible to Damage During a Flood Event?

The largest impact on communities from flood events is the loss of life and property. During certain years, property losses resulting from flood damage are extensive. Development in the floodplains of the City of West Covina will continue to be at risk from flooding because flood damage occurs on a regular basis throughout the county. Property loss from floods strikes both private and public property.

Property Loss Resulting from Flooding Events

The type of property damage caused by flood events depends on the depth and velocity of the floodwaters. Faster moving floodwaters can wash buildings off their foundations and sweep cars downstream. Pipelines, bridges, and other infrastructure can be damaged when high waters combine with flood debris. Extensive damage can be caused by basement flooding and landslide damage related to soil saturation from flood events. Most flood damage is caused by water saturating materials susceptible to loss (i.e., wood, insulation, wallboard, fabric, furnishings, floor coverings, and appliances). In many cases, flood damage to homes renders them unlivable.

Manufactured Homes

Statewide, the 1996 floods destroyed 156 housing units. Of those units, 61 % were mobile homes and trailers. Many older manufactured home parks are located in floodplain areas. Manufactured homes have a lower level of structural stability than stick-built homes, and must be anchored to provide additional structural stability during flood events. Because of confusion in the late 1980s resulting from multiple changes in NFIP regulations, there are some communities that do not actively enforce anchoring requirements. Lack of enforcement of manufactured home construction standards in floodplains can contribute to severe damages from flood events.

The City of West Covina utilizes State codes to regulate mitigation and hazards to manufactured homes and/or mobile homes. The City of West Covina Engineering Division requires the building floor to be 24 inches above any known floodplain.

There are two Manufactured Homes parks within the City of West Covina. The Rainbow Estates Park at 2131 San Bernardino Road and Friendly Village at 3033 Valley Blvd. The Rainbow Estates is in an area that may be impacted by the failure of Santa Fe Dam and is adjacent to the Big Dalton Wash. The Rainbow Estates is in a elevated area just north of Valley Boulevard, it is not located in an area susceptible to flooding.


Flood events impact businesses by damaging property and by interrupting business. Flood events can cut off customer access to a business as well as close a business for repairs. A quick response to the needs of businesses affected by flood events can help a community maintain economic vitality in the face of flood damage. Responses to business damages can include funding to assist owners in elevating or relocating flood-prone business structures.

Public Infrastructure

Publicly owned facilities are a key component of daily life for all citizens of the county. Damage to public water and sewer systems, transportation networks, flood control facilities, emergency facilities, and offices can hinder the ability of the government to deliver services. Government can take action to reduce risk to public infrastructure from flood events, as well as craft public policy that reduces risk to private property from flood events.


During natural hazard events, or any type of emergency or disaster, dependable road connections are critical for providing emergency services. Roads systems in the City of West Covina are maintained by multiple jurisdictions. Federal, state, county, and city governments all have a stake in protecting roads from flood damage. Road networks often traverse floodplain and floodway areas. Transportation agencies responsible for road maintenance are typically aware of roads at risk from flooding.


Bridges are key points of concern during flood events because they are important links in road networks, river crossings, and they can be obstructions in watercourses, inhibiting the flow of water during flood events. The bridges in the City of West Covina are state, county, city, and privately owned. A state-designated inspector must inspect all state, county, and city bridges every two years; but private bridges are not inspected, and can be very dangerous. The inspections are rigorous, looking at everything from seismic capability to erosion and scour.

The Holt Avenue Bridge in the City of West Covina is currently being upgraded by replacing the earthquake resistant bearing pads using city funds.

Storm Water Systems

Local drainage problems are not common in the City of West Covina. There is a drainage master plan, and City of West Covina public works staff are aware of local drainage threats. The problems are often present where storm water runoff enters culverts or goes underground into storm sewers. Because of the increase runoff from hardscaped surfaces inadequate maintenance can contribute to the flood hazard in urban areas. The City of West Covina utilizes a gravity system to move water into the Los Angeles County Flood Control storm channels.

There are eight electric lift stations located at each of the I-10 Freeway underpasses. These sites include the Cameron/I-10 underpass, West Covina Parkway/I-10 underpass, Sunset/I-10 underpass, Vincent/I-10 underpass, Lark Ellen/I-10 underpass, Azusa/I-10 underpass, Hollenbeck/I-10 underpass, Citrus/I-10 underpass. The City of West Covina has two other streets that transverse the I-10 corridor; Barranca Ave overpass, and the Grand Ave tunnel which is at street level grade.

Water/Wastewater Treatment Facilities

There are no wastewater/sewer treatment facilities in the City of West Covina. The City of West Covina utilizes a gravity system to flow wastewater, with two pump stations. The sewer lift stations are located at Quail Valley/Cameron and property at 2700 S. Azusa.

There are also eight water service companies and or districts in the City of West Covina:

  • City of Covina Water
  • Suburban Water Systems
  • City of Azusa Water
  • Valley County Water
  • Rowland Water District
  • Valencia Heights Water
  • Walnut Valley Water
  • San Gabriel Valley Water

Water Quality

Environmental quality problems include bacteria, toxins, and pollution. All of Suburban Water Systems reservoirs are topped, which would prevent them from becoming contaminated by runoff.

Existing Flood Mitigation Activities

Flood mitigation activities listed here include current mitigation programs and activities that are being implemented by the City of West Covina agencies or organizations.

The City of West Covina Codes

The City of West Covina uses building codes, zoning codes, and various planning strategies to address the goals which aim at restricting development in areas of known hazards, and applying the appropriate safeguards

Mitigation Requirements

Acquisition and Protection of Open Space in the Floodplain Current efforts to increase public open space in the City of West Covina have been paired with the need to restore and preserve natural systems that provide wildlife habitat and help to mitigate flood events. Public parks and publicly owned open spaces can provide a buffer between flood hazards and private property.

Water Districts

All of the water districts in the City of West Covina are in the process of replacing old cast iron pipes with more ductile iron pipes, which will be more resilient in disaster situations. During a disaster, water districts in the region work together to provide water for the City of West Covina citizens. The eight water companies that serve West Covina have interconnections to share resources for emergency situations.

Riparian Areas

Riparian areas are important transitional areas that link water and land ecosystems. Vegetation in riparian areas is dependent on stream processes, such as flooding, and often is composed of plants that require large amounts of water, such as willows and cottonwood trees. Healthy vegetation in riparian buffers can reduce streamside erosion. During flood events, high water can cause significant erosion. Population growth and development have strained the land and water resources, and the community has responded by supporting various improvement projects, such as the Heritage Park blue stream area.

Even though the City of West Covina does not have any year round watercourse, the City does have a number of seasonal streams with the largest of these contained with a cement walled flood control channel. The watercourses are: Walnut Creek (wash), Big Dalton Wash, Charter Oak Wash, San Jose Creek (wash) tributary from Nogales/Shakespeare, Vine Creek, Holt Avenue Creek, the watercourse emanating from the Galster Park drainage, the watercourse at Hidden Valley, the watercourse at Spring Meadow, the watercourse from BKK into the Puente Creek (wash), and the Heritage Park watercourse that drains down adjacent to Eddes Street. Any one of these at certain times of year can have enough water in them to be a factor on the local wildlife.

Storm water Systems

The City of West Covina is under the National Pollution Discharge Elimination System (N.P.D.E.S.) permit requirements in which Best Management Practices are used to reduce pollutants into the storm drains.

Erosion Control, also referred to as "soil stabilization" is the most effective way to retain soil on the construction site. The City asks that a Storm Water Pollution Prevention Plan be submitted by the developer to insure that Erosion Control is addressed during the construction period. The City Engineering Inspector oversees that the contractor preserves existing vegetation where feasible, to limit disturbance, and to stabilize and revegetate disturbed areas as soon as possible after grading or construction.

The City also requires that Best Management Practices are used at the appropriate locations along the site perimeter and at all operational internal inlets to the storm drain system at all times during the rainy season. Sediment Control practices may include filtration devices and barriers (such as fiber rolls, silt fence, etc).

Community Issues Summary

The City of West Covina works to mitigate problems regarding flood issues when they arise. However, funding, time and manpower are often unavailable, causing the problems to go unresolved. Some areas in the City of West Covina are more susceptible to flooding issues, and have incurred repetitive losses.

The City of West Covina recently received an updated copy of the FEMA FIRM map and is in the process of confirming and adopting that data.

The most recent flooding for the City of West Covina has been caused by poorly maintained channels and flood control features. A strong preventative maintenance program would best serve the City of West Covina in it's efforts to control flooding.

The development of the Sycamore Glen housing development at the southwest corner of Nogales and Shakespeare is adjacent to the Nogales Avenue drainage and has been studied and included in the CEQA report. The proposal is to develop 39 single family residential units, three duplex lots, an open space lot, and a 278,184 sq. ft. open space/stream bed lot adjacent to the stream drainage. This unnamed watercourse is a tributary stream to the San Jose Creek, which in turn flows into the San Gabriel River. The creek is considered a Jurisdictional Waters of the United States by the U.S. Army Corps of Engineers, and is classified a Streambed by the California Department of Fish and Game.

The development of Comstock Homes adjacent to the Holt Avenue Creek has been tied into the upgrade of the Holt Avenue bridge. This waterway is flanked by a number of large residential lots that could see future development into multiple single family homes.

Flood Mitigation Action Items

The flood mitigation action items provide direction on specific activities that organizations and residents in the City of West Covina can undertake to reduce risk and prevent loss from flood events. Each action item is followed by ideas for implementation, which can be used by the steering committee and local decision makers in pursuing strategies for implementation.

Short Term - Flooding #l: Mitigate flooding at Azusa and Amar Road.
Ideas for Implementation:
  • Improve drainage system throughout the area of Azusa Avenue and Amar Road, including runoff down Azusa Avenue.
  • Coordinate with rehabilitation of road development on issues involving drainage
  • Work with BKK on issues of developing and maintaining adequate drainage
  • Work with Shopping Centers at Azusa and Amar to improve drainage.
  • Any new development at the BKK site to include mitigation measures.
  • Coordinating Organization: Community Development Commission; Environmental
  • Management

Timeline: : Ongoing
Plan Goals Addressed: Protect Life and Property, Partnerships and Implementation
Constraints: Coordination with developers.

Short Term - Flooding #2: Recommend revisions to requirements for development within the floodplain, where appropriate
Ideas for Implementation:
  • Evaluate elevation requirements for new residential and nonresidential structures in the unincorporated floodplain area
  • Complete rebuild of the Holt and Grand Avenue bridge to include design to minimize flooding risk;
  • Explore raising the base elevation requirement for new residential construction to two or three feet above base flood elevation, or greater. An increased elevation standard is one activity the county can engage in to receive credit from the NFIP Community Rating System Program;
  • Identify opportunities to upgrade Federal Insurance Rate Map, and arrange for Cooperative Technical Partnership mapping upgrades for select areas; and
  • Identify alternatives to reduce development in the floodplain.

Coordinating Organization: Planning; Public Works
Timeline: 2 years
Plan Goals Addressed: Protect Life and Property
Constraints: Adoption of changes to the building code and/or zoning ordinances.

Short Term - Flooding #3: Target flooding mitigation information to the public.
Ideas for Implementation:
  • Identify properties eligible for Flooding Insurance. Provide information on the need and purpose of flood insurance.
  • Provide flooding mitigation materials to the public with information on proper use.
  • Distribute information regarding flooding to the general public.
  • Adopt new FIRM maps.

Coordinating Organization: Public Works, Risk Management
Timeline: 2 years
Plan Goals Addressed: Protect Life and Property, Emergency Services
Constraints: Adopt new FIRM map, develop Public Education materials.

Flood Resource Directory

The following resource directory lists the resources and programs that can assist county communities and organizations. The resource directory will provide contact information for local, county, regional state and federal programs that deal with natural hazards.

County Resources

Los Angeles County Public Works Department
900 S. Fremont Ave.
Alhambra, CA 91803
Ph: 626-458-5100

Sanitation Districts of Los Angeles County
1955 Workman Mill Road
Whittier, CA 90607
Ph: 562-699-7411 x2301

State Resources

Governor's Office of Emergency Services (OES)
P.O. Box 419047
Rancho Cordova, CA 95741-9047
Ph: 916 845-8911
Fx: 916 845-8910

California Resources Agency
1416 Ninth Street, Suite 1311
Sacramento, CA 95814
Ph: 916-653-5656

California Department of Water Resources (DWR)
1416 9th Street
Sacramento, CA 95814
Ph: 916-653-6192

California Department of Conservation: Southern California Regional Office
655 S. Hope Street, #700
Los Angeles, CA 90017-2321
Ph: 213-239-0878
Fx: 213-239-0984

Federal Resources and Programs

Federal Emergency Management Agency (FEMA)
FEMA provides maps of flood hazard areas, various publications related to flood mitigation, funding for flood mitigation projects, and technical assistance, FEMA also operates the National Flood Insurance Program. FEMA' s mission is to reduce loss of life and property and protect the nation's critical infrastructure from all types of hazards through a comprehensive, risk-based, emergency management program of mitigation, preparedness, response and recovery.

Federal Emergency Management Agency, Region IX
1111 Broadway, Suite 1200
Oakland, CA 94607
Ph: 510-627-7100
Fx: 510-627-7112

Federal Emergency Management Agency, Mitigation Division
500 C Street, S.W.
Washington, D.C. 20472
Ph: 202-566-1600

FEMA' s List of Flood Related Websites
This site contains a long list of flood related Internet sites from "American Heritage Rivers" to "The Weather Channel" and is a good starting point for flood information on the Internet. Contact: Federal Emergency Management Agency, Phone: (800) 480-2520


National Flood Insurance Program (NFIP)
In Southern California many cities lie within flood zones as defined in FEMA Flood Maps. The City of West Covina is a community within a designated flood zone. Flood insurance is available to citizens in communities that adopt and implement NFIP building standards. The standards are applied to development that occurs within a delineated floodplain, a drainage hazard area, and properties' within 250 feet of a floodplain boundary. These areas are depicted on federal Flood Insurance Rate Maps available through the county.
National Floodplain Insurance Program (NFIP)
500 C Street, S.W.
Washington, D.C. 20472
Ph: 202-566-1600

The Floodplain Management Association
The Floodplain Management website was established by the Floodplain Management Association (FMA) to serve the entire floodplain management community. It includes full-text articles, a calendar of upcoming events, a list of positions available, an index of publications available free or at nominal cost, a list of associations, a list of firms and consultants in floodplain management, an index of newsletters dealing with flood issues (with hypertext links if available), a section on the basics of floodplain management, a list of frequently asked questions (FAQs) about the Website, and a catalog of Web links.

Floodplain Management Association
P.O. Box 50891
Sparks, NV 89435-0891
Ph: 775-626-6389
Fx: 775-626-6389

The Association of State Floodplain Managers
The Association of State Floodplain Managers is an organization of professionals involved in floodplain management, flood hazard mitigation, the National Flood Insurance Program, and flood preparedness, warning, and recovery. ASFPM fosters communication among those responsible for flood hazard activities, provides technical advice to governments and other entities about proposed actions or policies that will affect flood hazards, and encourages flood hazard research, education, and training. The ASFPM Web site includes information on how to become a member, the organization's constitution and bylaws, directories of officers and committees, a publications list, information on upcoming conferences, a history of the association, and other useful information and Internet links.

Contact: The Association of State Floodplain Managers
Address: 2809 Fish Hatchery Road, Madison, WI 53713 Phone: (608) 274-0123


National Weather Service
The National Weather Service provides flood watches, warnings, and informational statements for rivers in the City of West Covina. National Weather Service
520 North Elevar Street
Oxnard, CA 93030
Ph: 805-988- 6615

Office of Hydrology, National Weather Service
The National Weather Service s Office of Hydrology (OH) and its Hydrological Information Center offer information on floods and other aquatic disasters, This site offers current and historical data including an archive of past flood summaries, information on current hydrologic conditions, water supply outlooks, an Automated Local Flood Warning Systems Handbook, Natural Disaster Survey Reports, and other scientific publications on hydrology and flooding.

National Weather Service, Office of Hydrologic Development
1325 East West Highway, SSMC2
Silver Spring, MD 20910
Ph: 301-713-1658
Fx: 301-713-0963

National Resources Conservation Service (NRCS), US Department of Agriculture
NRCS provides a suite of federal programs designed to assist state and local governments and landowners in mitigating the impacts of flood events. The Watershed Surveys and Planning Program and the Small Watershed Program provide technical and financial assistance to help participants solve natural resource and related economic problems on a watershed basis. The Wetlands Reserve Program and the Flood Risk Reduction Program provide financial incentives to landowners to put aside land that is either a wetland resource, or that experiences frequent flooding. The Emergency Watershed Protection Program (EWP) provides technical and financial assistance to clear debris from clogged waterways, restore vegetation, and stabilizing riverbanks. The measures taken under EWP must be environmentally and economically sound and generally benefit more that one property.

National Resources Conservation Service
14th and Independence Ave., SW, Room 5105-A
Washington, DC 20250
Ph: 202-720-7246
Fx: 202-720-7690

USGS Water Resources
This web page offers current US water news; extensive current (including real-time) and historical water data; numerous fact sheets and other publications; various technical resources; descriptions of ongoing water survey programs; local water information; and connections to other sources of water information.

USGS Water Resources
6000 J Street Placer Hall
Sacramento, CA 95819-6129
Ph: 916-278-3000
Fx: 916-278-3070


Bureau of Reclamation
The mission of the Bureau of Reclamation is to manage, develop, and protect water and related resources in an environmentally and economically sound manner in the interest of the American public. The Bureau provides leadership and technical expertise in water resources development and in the efficient use of water through initiatives including conservation, reuse, and research. It protects the public and the environment through the adequate maintenance and appropriate operation of Reclamation's facilities and manages Reclamation's facilities to fulfill water user contracts and protect and/or enhance conditions for fish, wildlife, land, and cultural resources.

Mid Pacific Regional Office
Federal Office Building
2800 Cottage Way
Sacramento CA 95825-1898
Ph: 916- 978-5000
Fax 916- 978-5599

US Army Corps of Engineers
The Corps of Engineers administers a permit program to ensure that the nation's waterways are used in the public interest. Any person, firm, or agency planning to work in waters of the United States must first obtain a permit from the Army Corps of Engineers. The Corps is responsible for the protection and development of the nation's water resources, including navigation, flood control, energy production through hydropower management, water supply storage and recreation.

US Army Corps of Engineers
P.O. Box 532711
Los Angeles CA 90053-2325
Ph: 213-452-3921 Army Corps of Engineers

Other National Resources
American Public Works Association
2345 Grand Boulevard, Suite 500
Kansas City, MO 64108-2641
Ph: 816-472-6100
Fx: 816-472-1610


NFlP Community Rating System Coordinator's Manual
Indianapolis, IN.
This informative brochure explains how the Community Rating System works and what the benefits are to communities. It explains in detail the CRS point system, and what activities communities can pursue to earn points. These points then add up to the "rating" for the community, and flood insurance premium discounts are calculated based upon that "rating " The brochure also provides a table on the percent discount realized for each rating (1-10). Instructions on how to apply to be a CRS community are also included.
Contact: NFIP Community Rating System
Phone: (800) 480-2520 or (317) 848-2898

Floodplain Management: A Local Floodplain Administrator's Guide to the NFlP
This document discusses floodplain processes and terminology. It contains floodplain management and mitigation strategies, as well as information on the NFIP, CRS, Community Assistance Visits, and floodplain development standards.

Contact: National Flood Insurance Program Phone: (800) 480-2520 Website: http://www.fema,gov/nfip/

Flood Hazard Mitigation Planning: A Community Guide, (June 1997).
Massachusetts Department of Environmental Management.
This informative guide offers a 10-step process for successful flood hazard mitigation. Steps include: map hazards, determine potential damage areas, take an inventory of facilities in the flood zone, determine what is or is not being done about flooding, identify gaps in protection, brainstorm alternatives and actions, determine feasible actions, coordinate with others, prioritize actions, develop strategies for implementation, and adopt and monitor the plan.

Contact: Massachusetts Flood Hazard Management Program Phone: (617) 626-1250 Website: Reducing Losses in High Risk Flood Hazard Areas: A Guidebook for Local Officials, (February 1987), FEMA-116.
This guidebook offers a table on actions that communities can take to reduce flood losses. It also offers a table with sources for floodplain mapping assistance for the various types of flooding hazards. There is information on various types of flood hazards with regard to existing mitigation efforts and options for action (policy and programs, mapping, regulatory, non-regulatory). Types of flooding which are covered include alluvial fan, areas behind levees, areas below unsafe dams, coastal flooding, flash floods, fluctuating lake level floods, ground failure triggered by earthquakes, ice jam flooding, and mudslides.
Contact: Federal Emergency Management Agency Phone: (800) 480-2520
Website: http://www.fema,gov

Section 8 - Flood Endnotes

i. ii. Gumprecht, Blake, 1999, Johns Hopkins University Press, Baltimore, MD. iii.,0,1754871.story?coll=la-adelphia-right-rail iv.
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