ALERT Low Water Crossing ALERT Low Water Crossing Warning SystemsWarning Systems

Produced by

Rand Allan, Associate Meteorologist

County of San Diego Flood Control

The Need for Low Water The Need for Low Water Crossing Warning Crossing Warning SystemsSystems

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 Low Water Crossing Warning DevicesWarning Devices

ThreeExamples

Stand-Alone SystemStand-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

Warning Flasher - Scottsdale, AZ

•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

Automated ALERT Automated ALERT SignalsSignals

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

ALERT Flasher - Harmony Grove, CA

•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 Signal/Barrier ALERT Signal/Barrier SystemSystem

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

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

Benefits of Warning Benefits of Warning SystemsSystems

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

ConsiderationsConsiderations

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

For further information, please contact:

Rand Allan (858) 495-5557

e-mail: rallanpw@co.san-diego.ca.us

Low Water Crossing Systems