Mud Flood at Sierra Madre (1954) Video

Mudslides and floods triggered by the combination of heavy rainfall, steep slopes, and loose soil, earth movements in Sierra Madre have been historically preceded by major wildfires. Ashy slopes left denuded by wildfires have been especially susceptible to "mudslides" during and immediately after rainstorms. Since many Sierra Madre residents live down slope of wildfire areas, the community is at risk of mudslides and other earth movements. Dam failure is considered remote, and the only significant threat would be urban flooding. There is a future potential for flooding due to higher density development, which increases rapid water run off during heavy rains. The City has to continually prepare and mitigate by upgrading its storm drain infrastructure as population increases.

What is susceptible to landslides?
Landslides can affect utility services, transportation systems, and critical lifelines. Communities may suffer immediate damages and loss of service. Disruption of infrastructure, roads, and critical facilities may also have a long-term effect on the economy. Utilities, including potable water, wastewater, telecommunications, natural gas, and electric power are all essential to service community needs. Loss of electricity has the most widespread impact on other utilities and on the whole community. Natural gas pipes may also be at risk of breakage from landslide movements as small as an inch or two.

Roads and Bridges
Sierra Madre losses incurred from landslide hazards have been associated primarily with roads. The City of Sierra Madre Public Works Department is responsible for responding to slides that inhibit the flow of traffic or damage roadways. The Public Works Department does its best to communicate with residents impacted by landslides, but can usually only repair the road itself, as well as the areas adjacent to the slide where the city has the right of way. There has been only one documented loss to one of eight small bridges in Sierra Madre. This loss occurred as a debris flow conveyed through the County-owned flood control channel and wiped out the small bridge in its entirety. The County of Los Angeles Public Works is responsible for maintaining the flood control channel that the eight small bridges traverse.

It is not cost effective to mitigate all slides because of limited funds and the fact that some historical slides are likely to become active again even with mitigation measures. The Sierra Madre Public Works Department alleviates problem areas by grading slides, and by installing new drainage systems on the slopes to divert water from the landslides. This type of response activity is often the most cost-effective in the short-term, but is only temporary.

Lifelines and Critical Services
Lifelines and critical facilities should remain accessible, if possible, during a natural hazard event. The impact of closed transportation arteries may be increased if the closed road or bridge is critical for hospitals and other emergency facilities. Therefore, inspection and repair of critical transportation facilities and routes is essential and should receive high priority. Losses of power and phone service are also potential consequences of landslide events. Due to heavy rains, soil erosion in hillside areas can be accelerated, resulting in loss of soil support beneath high voltage transmission towers in hillsides and remote areas. Flood events can also cause landslides, which can have serious impacts on gas lines that are located in vulnerable soils.

What is Susceptible to Damage in 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 Sierra Madre will continue to be at minimal risk from flooding because flood damage doesn’t occur 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 flood waters. Faster moving flood waters 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.

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-12 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 Sierra Madre 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. 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 City of Sierra Madre has eight small bridges that traverse a Los Angeles County flood control channel. This channel is maintained by the County and the bridges are inspected by the City and the County every two years.

Storm Water Systems
Local drainage problems are common throughout the City of Sierra Madre. Drainage is addressed in the City’s General Plan, and City of Sierra Madre public works staff is aware of local drainage problem areas. The problems are often present where storm water runoff enters culverts or enters low lying properties.

Water/Wastewater Treatment Facilities
Wastewater derived from Sierra Madre is conveyed to the Los Angeles County Sanitation Districts wastewater treatment facility in Whittier. The City of Sierra Madre provides water to the residents as part of its City services.

Water Quality
Environmental quality problems include bacteria, toxins, and pollution. The City of Sierra Madre has a comprehensive storm water pollution prevention program that is designed to educate residents, contractors, developers, businesses and schools that only storm water should be allowed to enter the storm drain system. We also contract 13 with the County of Los Angeles Public Works to perform annual catch basin cleaning. In conjunction with this annual cleaning the City of Sierra Madre also cleans out catch basins in high traffic areas monthly.

Flood Mitigation Activities

The City of Sierra Madre Codes
The City of Sierra Madre 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

The City of Sierra Madre Municipal Code § 15.04.070 prohibits:

• Construction upon, destruction or curtailment in the capacity of storm drain facilities installed under and by virtue of Title 17 of the code

• Construction, excavation or fill which changes the grade of the natural slope of the surface of any lot or lots so that the water drainage thereon is changed to run onto a different location or in greater quantity or at an accelerated rate, or in a way that creates a hazard to the public health, safety or property. The decision of the building inspector shall be based upon the recommendation of the city engineer concerning the continued necessity of such drainage installations or of reasonable substitutes therefore.

• …run onto a different location or in greater quantity or at an accelerated rate, or in a way that creates a hazard to the public health, safety or property. The decision of the building inspector shall be based upon the recommendation of the city engineer concerning the continued necessity of such drainage installations or of reasonable substitutes therefore.