Overview

Orange County initiated its ALERT System in 1983 when a need was identified for additional quantitative weather 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. Since its inception ALERT has grown in versatility and sophistication.

The Orange County ALERT System consists of three computer base stations and three radio repeaters. The radio repeater located on Santiago Peak receives and re-transmits telemetry from field sensors located in Los Angeles, San Bernardino, and Orange Counties. One of the two receiver base stations located at the OC Public Works yard on Glassell Street in Orange is a server connected to the OC Public Works Department Intranet. It provides access to OC Public Works Department personnel from their desktop computer workstations. In response to extreme weather conditions the OC Public Works - Department Operations Center (DOC) opens to coordinate monitoring and response to threats of flooding, mudslides, and debris flows. The ALERT System provides continuous weather information to the DOC during its period of operation.

BASE STATIONS

The Glassell ALERT Base Station consists of three networked computer servers and uses three receiver-decoders to receive telemetry data from the repeaters located in Southern California. A dedicated internet link is used to receive data from a Corps of Engineers computer in Los Angeles.

ALERT rain Guage Station

MONITORING STATIONS

Hydrologic data and equipment status information are transmitted from field stations by radio telemetry to the ALERT base station server. The Orange County 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 or reservoir water levels. Other sensors monitor temperature, wind speed, wind direction, transmitter/datalogger battery voltage, and barometric pressure.

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

Santa Ana River Basin

Originating in the San Bernardino Mountains, the Santa Ana river flows through San Bernardino, Riverside, and Orange Counties and discharges into the Pacific Ocean just north of Newport Beach. The Santa Ana River Basin has been identified as having one of the worst flooding potentials west of the Mississippi River. An extensive network of rain gauges 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.

Orange County Watersheds

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, ALERT data additionally supports fluvial sediment monitoring programs and other federally mandated water quality monitoring programs in Orange County.

Tide Stations

Water-level sensors have also been used to monitor the effects of tide on two flood control channels in Huntington Beach. In 1983, the Talbert Channel levee was overtopped in Huntington Beach causing major flood damage to adjacent neighborhoods. Extreme tides during periods of heavy rainfall drastically reduced the ability of the flood control channel to discharge stormwater runoff to the ocean and emphasized the need for real time monitoring. Water level sensor have been installed on the Huntington Beach Channel at Magnolia Avenue and on the Talbert Channel at Brookhurst Street. The sensor on the Talbert Channel is also used to monitor blockage of the channel outlet. When blockage occurs, OC Public Works initiates a maintenance activity to clear the blockage and restore tidal flushing to the Talbert Wetlands.

Tide Stations

DATA PRESENTATION

Data are presented as text, graphical images, and maps displayed on the ALERT base station computers and the DOC color monitors. Map displays show the relative locations of rain gauges 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 can also show detailed information for a sensor location or a group of sensors. The information displayed can include instantaneous (e.g. water level, temperature, wind speed, direction, barometric pressure, or relative humidity) or cumulative data (rainfall) for twenty-four hour and/or seven days. Other outputs include numeric data, bar charts, and time series graphs for rainfall, water level, rate of change, and rated flow.

The ALERT system has a programmable report generator which allows creation 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 Zone Forecast / Basin Average rainfall report. The reports can be run with any desired ending time. The ALERT System has been programmed to generate two ALERT System maintenance reports: 1) Orange County Sensor report 2) ACOE sensor report. The maintenance reports list the time, date and value of the last transmitted data