Public Safety Concerns

Will the Wash Continue to Serve its Purpose?

In 1937, the Verdugo Wash was lined in concrete to prevent future flooding after after massive storm and resulting flood in 1934 killed dozens and damaged numerous properties in the Crescenta Valley area. The concrete wash was constructed to handle the type of once-in-every-50-year storm events such as occurred in 1934.

Effects of the local building boom over the past 20 years, however, now call into question whether the wash currently has sufficient capacity to handle a 50-year storm event. Construction of a path within the wash would lessen the ability of the wash to convey the amount of storm runoff for which it was built.

Flood hazard increases when developments encroach into floodplains. Recently relaxed zoning regulations that allow increased development in single family zones, along with unprecedented construction activity over the past 20 years, has created a significant increase of impervious areas which are unable to absorb rainwater, thus creating additional water runoff into storm drains and the wash.

This additional storm runoff already taxes the capacity of the wash and any construction activity for bike paths within the wash, especially in high fire zones, will significantly impact the flood control systems’ performance.

Impervious

Impervious areas are hard surfaces, such as buildings, concrete driveways, sidewalks, patios or streets, that allow little to no stormwater infiltration. When it rains, water runs off these impervious surfaces into flood control channels instead of being absorbed into the ground. An increase in impervious surfaces will also increase the amount of storm runoff to be handled by the Wash, which was designed over 80 years ago to handle a specific volume of water .

Fire Hazard = Flooding

Wildfires, which have not occurred in the Verdugo Mountains for over 60 years, dramatically change landscape and ground conditions, which can lead to increased risk of flooding during heavy rains, as the burn areas are unable to absorb the falling rain. Even modest rainstorms over a burned area can result in flash flooding downstream.

While the Verdugo Wash has done its job in the past to protect nearby homes and businesses from flooding, since the nearby hillsides have not burned for decades, its capacity truly has not been tested by a rainstorm event after a fire. Construction of raised platform trails within the wash would have the potential of causing the wash to become clogged with debris as the rainwater and debris would need to pass through a smaller channel beneath these raised platforms.

Flooding Rescues Likely

Below are two videos of swift-water rescues of people caught by flash floods during a heavy rainfall in the neighboring L.A. River. In some wider sections of the Verdugo Wash, the plan is to retain an open waterway down the middle, with paths along the sides. This type of design could result in the need for swift-water rescues should a trail-user fall into the open waterway during a storm event.

More Dense Zoning Could Increase Flooding

Much has changed since 1934. Current channels, wash and other storm water drainage systems in the city were long past due for a comprehensive study for flood control and prevention, even before the recently approved state assembly bill SB68 which allows the construction of ADUs and SB9 which allows for additional units in single family zones.

The most recent flood hazard study for the Glendale area was performed in 2003, approximately two decades ago, after which unprecedented construction activity and development have taken place, along with up-zoning of single family areas, which will result in massive construction activities in the near future.

Data reviewed for this 2003 study suggest that Southern California has experienced more wet years in the last 20-30 years than in the previous 50 years. According to the study, Gage Station F252-R, which is located at the southwestern end of the Verdugo Wash and has been in continuous operation since December of 1935, shows that the maximum daily peak flows in the lower reaches of the wash are typically less than 100 cubic feet per second (cfs). However, maximum daily peak flows have reached 1,000 cfs nine times since 1935, with a maximum peak flow of 1,850 cfs measured in 1968-69.

With the unprecedented amount of new construction in the area over the past 20 years, which has led to a large increase of impervious surfaces, the VWNC believes that the City of Glendale should perform a more recent Flood Hazards study prior to considering any new development within the wash. 

Read the 2003 study here:
https://www.glendaleca.gov/home/showpublisheddocument/4547/635242148308170000

The base flood, which has a 1% probability of exceedance in one year, is used by Federal agencies, as well as most county and State agencies to administer floodplain management programs. The goals of floodplain management are to reduce losses caused by floods while protecting the natural resources and functions of the floodplain. The basis of floodplain management is the concept of the “floodway”. FEMA defines this as the channel of a river or other watercourse, and the adjacent land areas that must be kept free of encroachment, in order to discharge the base flood without cumulatively increasing the water surface. The community is responsible for prohibiting encroachments into the floodway, unless it is demonstrated by detailed hydrologic and hydraulic analyses, that the proposed development will not increase the flood levels downstream.

Swift-moving storm runoff in the Verdugo Wash after a mild rainstorm.