Get Ready & Prepare

Flooding and Winter Storms

Overview

Flooding is the accumulation of water where usually none occurs or the overflow of excess water from a stream, river, lake, reservoir, or coastal body of water onto adjacent floodplains. Floodplains are lowlands adjacent to water bodies that are subject to recurring floods. Floods are natural events that are considered hazards only when people and property are affected. Nationwide, floods result in more deaths than any other natural hazard. Physical damage associated with floods includes the following:

• Inundation of structures, causing water damage to structural elements and contents.
• Erosion or scouring of stream banks, roadway embankments, foundations, footings for bridge piers, and other features.
• Impact damage to structures, roads, bridges, culverts, and other features from high-velocity flow and from debris carried by floodwaters. Debris may also accumulate on bridge piers and in culverts, increasing loads on these features or causing overtopping.
• Destruction of crops, erosion of soil, and deposition of debris and sediment on croplands.
• Release of sewage and hazardous or toxic materials as wastewater treatment plants are inundated, storage tanks are damaged, and pipelines are severed.

Floods also result in economic losses through closure of businesses and government facilities, disrupt communications, disrupt the provision of utilities such as water and sewer service, result in excessive expenditures for emergency response, and generally disrupt the normal function of a community.

In Monterey County four types of flooding occur: riverine flooding, coastal flooding, flash flooding, and storm water runoff flooding.

• Coastal Flooding: Coastal or tidal floods are characterized by inundation of normally dry lands by bay waters, often caused by extreme high tide events that result in shallow flooding of low-lying coastal areas. Coastal flooding in Monterey County is generally associated with Pacific Ocean storms in the months of November through February. Coastal flooding in conjunction with high tides and strong winds is a significant hazard.
• Riverine Flooding: Riverine flooding is overbank flooding of rivers and streams. 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. Riverine floodplains range from narrow, confined channels in the steep valleys of mountainous and hilly regions to wide, flat areas in plains and coastal regions. The amount of water in the floodplain is a function of the size and topography of the contributing watershed, the regional and local climate, and land use characteristics.
• Flash Flooding: The National Weather Service defines a flash flood as a rapid and extreme flow of high water into a normally dry area, or a rapid water level rise in a stream or creek above a predetermined flood level.>Flash floods can tear out trees, undermine buildings and bridges, and scour new channels. In urban areas, flash flooding is an increasingly serious problem due to removal of vegetation and replacement of ground cover with impermeable surfaces such as roads, driveways, and parking lots. The greatest risk from flash floods is occurrence with little to no warning. Major factors in predicting potential damage are intensity and duration of rainfall, and steepness of watershed and streams.
• Localized Storm Water Flooding: Urban storm drain pipes and pump stations have a finite capacity, and prolonged heavy rainfall contributes to a large volume of runoff resulting in high peak flows of moderate duration. When rainfall exceeds this capacity, or the system is clogged, water accumulates in the street until it reaches a level of overland release. Storm water flooding may occur outside of recognized drainage channels or delineated floodplains due to a combination of locally heavy precipitation, increased surface runoff, and inadequate facilities for drainage and storm water conveyance. Such events frequently occur in flat areas and in urbanized areas with large impermeable surfaces. Local drainage may result in “nuisance flooding,” in which streets or parking lots are temporarily closed, and minor property damage occurs.

History

Historic records show flooding and flood damage have occurred on a fairly regular basis (every few years) within Monterey County. Recent events that caused sever flood damage occurred in:

• 2016: Monterey County was hit with several significant storm events during the 2016 El Niño winter. The first one took place on January 19, 2016, the second from March 5 and 6, 2016, and the third on March 11, 2016. These storms caused severe roadway damage totaling $7,318,000 in repair costs.
• 2017: A series of atmospheric river events in January and February of 2017 caused widespread roadway flooding and damage in Monterey County. Combined, the January and February storms caused an estimated $52 million to County roads.
• 2019: An atmospheric river caused widespread heavy rainfall, roadway flooding, and strong winds. This caused flash flooding in Chualar where homes were flooded, and cars were stranded on a flooded highway. This event caused an estimated $2 million in damages.

Flood Risk

The principal factors affecting flood damage are flood depth and velocity. The deeper and faster flood flows become, the more damage they can cause. Shallow flooding with high velocities can cause as much damage as deep flooding with slow velocity. This is especially true when a channel migrates over a broad floodplain, redirecting high velocity flows and transporting debris and sediment. Although jurisdictions can implement mitigation and take preventative actions to significantly reduce the severity and threat of flood events, some type of residual risk will always exist (i.e., risk of a hazard event occurring despite technical and scientific measures applied to prevent it). Threats associated with residual risk include failure of a reservoir, a dam, levee, or other infrastructure, or a severe flood event that exceeds flood design standards or drainage capacity.

Flood risk has increased with population and urbanization. Increased impervious surfaces and channelization of streams has resulted in increased runoff and intensified flood flows. Increased development in floodplains has put more property and lives at risk for flooding. The damages caused by flooding in the Salinas Valley today, even with the construction of major flood control infrastructure, are far more substantial than they were a century ago. Along the Big Sur coast, streams and rivers draining the steep coastal mountains are subject to short, intense floods, capable of producing significant damage to property. Wildfires also exacerbate flood risk in Big Sur, denuding areas of vegetation, which can lead to increased sheet flow and greater velocities during subsequent rainstorms and causing water quality problems in coastal waters. The impact and severity of coastal flooding is additionally affected by tides, storm surge (the rise in water from wind stress and low atmospheric pressure), waves, and peak still-water elevation.

Prepare for Flooding

Make a Plan for your household, including your pets, so that you and your family know what to do, where to go, and what you will need to protect yourselves from flooding. Learn and practice evacuation routes, shelter plans, and flash flood response. Gather supplies, including non-perishable foods, cleaning supplies, and water for several days, in case you must leave immediately or if services are cut off in your area. Make sure to Sign up for Alerts.

Know Your Risk for Floods and Purchase Flood Insurance

Visit FEMA's Flood Map Service Center to know types of flood risk in your area. Purchase or renew a flood insurance policy. Homeowner’s insurance policies do not cover flooding. It typically takes up to 30 days for a policy to go into effect so the time to buy is well before a disaster. Get flood coverage under the National Flood Insurance Program (NFIP).

In Case of Emergency

Keep important documents in a waterproof container. Create password-protected digital copies. Protect your property. Move valuables to higher levels. Declutter drains and gutters. Install check valves. Consider a sump pump with a battery.

Stay Safe During a Flood

• Evacuate immediately, if told to evacuate. Never drive around barricades. Local responders use them to safely direct traffic out of flooded areas.
• Contact your healthcare provider If you are sick and need medical attention. Wait for further care instructions and shelter in place, if possible. If you are experiencing a medical emergency, call 9-1-1.
• Listen to EAS, NOAA Weather Radio or local alerting systems for current emergency information and instructions regarding flooding.
• Do not walk, swim or drive through flood waters. Turn Around. Don’t Drown!
• Stay off bridges over fast-moving water. Fast-moving water can wash bridges away without warning.
• Stay inside your car if it is trapped in rapidly moving water. Get on the roof if water is rising inside the car.
• Get to the highest level if trapped in a building. Only get on the roof if necessary and once there, signal for help. Do not climb into a closed attic to avoid getting trapped by rising floodwater.

Stay Safe After a Flood

• Pay attention to authorities for information and instructions. Return home only when authorities say it is safe.
• Avoid driving except in emergencies.
• Wear heavy work gloves, protective clothing and boots during clean up and use appropriate face coverings or masks if cleaning mold or other debris.
• People with asthma and other lung conditions and/or immune suppression should not enter buildings with indoor water leaks or mold growth that can be seen or smelled. Children should not take part in disaster cleanup work.
• Be aware that snakes and other animals may be in your house.
• Be aware of the risk of electrocution. Do not touch electrical equipment if it is wet or if you are standing in water. Turn off the electricity to prevent electric shock if it is safe to do so.
• Avoid wading in floodwater, which can be contaminated and contain dangerous debris. Underground or downed power lines can also electrically charge the water.
• Use a generator or other gasoline-powered machinery ONLY outdoors and away from windows.

Additional Resources

• Flood Information Sheet(PDF)
• Protective Actions Research for Flood
• National Flood Insurance Program (NFIP)
• Flood Insurance Facts
• Six Things to Know Before a Disaster(Video)
• When the Cloud Forms(Video)
• How to Prepare for a Flood
• File A Flood Insurance Claim
• Your Homeowners Insurance Does Not Cover Flood(PDF)
• American Red Cross