ALERT Low Water Crossing Warning Systems Produced by Rand Allan, Associate Meteorologist County of San Diego Flood Control

The Need for Low Water Crossing Warning Systems Flooding claims scores of lives each year Each foot of water rise displaces up to 1500 lbs of vehicle weight Lateral force of a flooding stream can place over 500 lbs of force on a vehicle Small vehicles and pedestrians can be swept off the road in as little as 6”-12” of water Flood waters can hide washed-out crossings

Low Water Crossing Warning Devices Three Examples

Warning Flasher - Scottsdale, AZ Stand-Alone System Warning light activates when water over the road Good for remote, lightly traveled areas with little accident history However, there is no notification given to authorities Relatively inexpensive, cost about $1,000 -$2,000 Can be built in-house For about $2,500 more they can be modified for ALERT radio transmission Warning Flasher - Scottsdale, AZ

Automated ALERT Signals Under control of ALERT system As water first flows over road, lights flash yellow; sign says use caution when crossing As water reaches 6” over road, lights flash red, sign changes to road closed condition Sensor can be installed to detect washed-out road Station can phone agencies to warn of flood events Agencies can phone station to get current conditions Cost is moderate, about $15,000 to $20,000 Good for moderate traffic areas with low accident rate ALERT Flasher - Harmony Grove, CA

ALERT Signal/Barrier System Station will call agencies to warn of flooding Agencies can call station to get current status of crossing Closed circuit loop in road can detect road washout and close barriers Installation is useful where heavy traffic causes a high rate of incidents Installation is expensive - $100,000 to $150,000 Under control of ALERT System Barriers prevent crossing the stream when water depth reaches 6” over road Sensors in road prevent motorists from becoming trapped between barriers ALERT transmits water levels and times of road closings ALERT Flasher/Barrier - Spring Valley, CA

Benefits of Warning Systems Real-time water levels for crossing safety Immediate notification of start and end of road flooding and closure Reduced overtime costs waiting for roads to flood Road crews can attend to other priorities Legal protection for gov’t agencies No excuses for not knowing it was hazardous to cross

Considerations Requires dedicated maintenance Initial cost can be quite expensive Design of system has to match the needs of the low water crossing Procedures need to be established between agencies Legal regulations may need to be established

Low Water Crossing Systems For further information, please contact: Rand Allan (858) 495-5557 e-mail: rallanpw@co.san-diego.ca.us