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

2. 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

3. Low Water Crossing Warning Devices
Three
Examples

4. 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

5. 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

6. 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

7. 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

8. 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

9. Low Water Crossing Systems
For further information, please contact:
Rand Allan (858)