Orange County began the installation of its ALERT System in 1983 when a need was identified for additional quantitative information to support storm operations personnel. ALERT met this need, offering real-time data from automatic field sensors located in flood threatened areas. Relatively low cost sensors were initially installed along the Santa Ana River and in four South County Channels, San Juan Creek, Arroyo Trabuco Creek, Oso Creek, and Aliso Creek. The system has subsequently been expanded to monitor other flood control channels and retarding basins. 

ALERT is an acronym for Automated Local Evaluation in Real Time, which is a method of using remote sensors in the field to transmit environmental data to a central computer in real time. This standard was developed in the 1970's by the National Weather Service and has been used by the National Weather Service, Army Corps of Engineers, Bureau of Reclamation, numerous state and local agencies, and international organizations. In the intervening period, the system has grown in versatility and sophistication, with changes evident on an annual basis.

The Orange County ALERT System consists of two computer base stations and three radio repeaters. The two radio repeaters located on Santiago Peak receive and retransmit telemetry from field sensors located in Los Angeles, Riverside, San Bernardino, and Orange Counties. One of the two base stations located at Katella Yard is a server connectected to the RDMD Intranet and provides access to RDMD personnel from their desktop computer workstations.

The Katella Yard ALERT Base Stations consists of one networked computer server and one stand alone computer workstation. The Katella Yard base stations use three receiver-decoders to receive telemetry data from repeater stations located in Southern California. A dedicated telephone line is used to receive data from a Corps of Engineers computer in Los Angeles.

MONITORING STATIONS

Hydrologic data and equipment status information is transmitted from field stations by radio telemetry to the ALERT base station computers. The ALERT system monitors a total of 338 sensors within Southern California (Santa Barbara, Ventura, Los Angeles, San Bernardino, Riverside, and Orange Counties). Of the 338 sensors 214 are used to monitor precipitation and 54 for flood control channel and reservoir water levels, other sensors monitor temperature, wind speed, wind direction, battery voltage, and barometric pressure. The water level sensor locations in Orange County have been selected on the basis of existing stream gaging stations on major storm channels, retarding basins, and dams.

Data from 58 of the monitored stations is received by dedicated phone line connected directly to the Army Corps of Engineers (ACOE) telemetry system computer located in Los Angeles. The phone line was installed in 1988. The majority of these ACOE stations are located in the upper Santa Ana River (SAR) watershed.

Originating in the San Bernardino Mountains, the Santa Ana river flows through San Bernardino, Riverside, and Orange Counties and discharges into the Pacific Ocean north of Newport Beach. The Santa Ana River Basin has been identified as the potential flood danger west of the Mississippi. An extensive network of rain gages and water-level sensors has been established in the Upper Santa Ana River Basin by the Corps of Engineers, San Bernardino, Riverside, and Orange Counties. This network of sensors runs from the San Gabriel, San Bernardino, and San Jacinto Mountains to Santa Ana.

ALERT sensors have been installed in all the major watersheds located in Orange County. Although the primary purpose of the sensors is for flood warning and detection  real time ALERT data is currently used to support sediment monitoring programs, and water quality sampling programs in Orange County.

Tide Stations

In 1983, the levee on Talbert Channel in Huntington Beach overtopped, causing major flood damage to adjacent neighborhoods. The flooding was caused by high tide conditions, which prevented the discharge of storm flows into the ocean.

Wetlands restoration has been done near the mouth of the Santa Ana River with a new outlet to the ocean built for Talbert Channel. This outlet can become blocked during high surf conditions preventing tidal flushing of the wetlands. RDMD is responsible for reopening the outlet within seven days of becoming blocked. Two tide water-level sensors have been installed to monitor conditions in the channel and wetlands, one at Brookhurst Street and one at Magnolia Avenue in Huntington Beach.

Automatic pump stations regulate the discharge of storm water to downstream flood control channels from retarding basins where water accumulates during storms. ALERT telemetry was installed at three pump stations in 1988, Huntington Beach,  Cypress, and Seal Beach, and at two additional stations in 1993, Los Alamitos and Harbor-Edinger. With the completion of South Park pump station monitoring was increased to a total of six pump stations.

The ALERT system uses 44 sensors to monitor the status of the six pump stations, i.e. which pumps are on or off, pump speed, flow rate, and water level. In the event of a problem, the monitoring system automatically dials the Orange County pager system and pages the pump station operation personal with an alphanumeric status message indicating the nature of the problem. This capability ensures that pump station staff are immediately made aware of the problem.

Data is presented as text, graphical images, and maps displayed on the ALERT base station computers and the Storm Operations Center color monitors. Map displays show the relative locations of rain gages and indicate precipitation amounts (in inches) at each station. Cumulative values displayed on rainfall maps are programmed to change color at five (yellow) and ten (red) year return frequencies. The time period covered by each graphics map display is indicated on the upper right side of the map.

Graphical image displays generally show detailed information for a sensor location, pump station, or a group of sensors. The information displayed can include instantaneous or cumulative data for twenty-four hour and/or seven days. Graphics displays include numeric data, bar charts, and strip charts for rainfall, water level, rate of change, and rated flow.

The ALERT system has a programmable report generator which allows setting up of custom data reports. The report generator has been programmed to automatically generate three operational reports: 1) a three day rainfall report for the County, 2) a County Dams and Reservoirs report, 3) and a Forecast Zone / Basin Average rainfall report.. The reports can be run with any desired ending time. The ALERT System has been programmed to generate three ALERT System maintenance reports: 1) a Orange County Sensor report, 2) a Pump Stations Sensor report, 3) and a ACOE sensor report.. The maintenance reports list the time, date and value of the last transmitted data value.

Content Listing

Alert System
Repeater Stations
Field Stations
Return Frequencies

Weather Forecasts EMWIN

Weather Imaging