Regional Infiltration and Inflow Control Program

Out in the Field - Finding and Fixing I/I > Rainfall Monitoring

Rainfall Monitoring

Rainfall Monitoring: The accurate measurement and reporting of rainfall quantities is necessary to provide a credible basis for the Local Agency flow data identified by the Regional I/I Control Program. The Earth Tech team is utilizing the rainfall data collected from a total of 73 rain gauges located throughout King and Snohomish County. The collected rain gauge data will be input and utilized with the CALAMAR rainfall system to generate accurate rainfall quantities in the I/I Control Program study area. The CALAMAR system is a French rainfall system, developed by RHEA, Inc., that will combine the network of rain gauges with the Natural Weather Service NEXRAD radar to provide rainfall measurements with more accuracy than is available from rain gauges alone.

The advent of National Weather Service's NEXRAD weather radar provides a major advance in our ability to locate and track rainfall with geographic precision. With the addition of CALAMAR, it is possible to have reliable, geographically precise and accurate rainfall measurements over an entire service area.

CALAMAR

CALAMAR (CAlcul de LAMes d'eau a l'Aide du Radar - Calculating Rain with the Aid of Radar) calibrates and processes the NEXRAD data in a unique and patented way that produces rainfall measurements with a typical accuracy of +/- 10%. This is a far higher degree of accuracy than is available from "raw" radar data, or from rain gauges alone. Accurate rainfall measurements take much of the uncertainty out of calculating relationships between rainfall and RDII whether it is by modeling or direct measurement.

CALAMAR can:

• Provide rainfall measurements with an accuracy of +/-10%.
• Provide measurements over various geographic areas in a 11,000 square mile region.
• Provide geographic resolution of 1 km2 (0.4 square mile).
• Provide an accurate short term forecast of rainfall intensity in a real-time mode.

Output

CALAMAR's basic output is accurate rainfall in 5 minute steps integrated over any geographic mini-basin, basin or Component Agency Boundary. These areas can be overlapping such that rainfall can be simultaneously calculated for each of the County's Service Basins, each Component Agency area and each RDII mini-basin established for this study.

Outputs for each area:

Hyetographs for each basin
Hyetographs are graphs that show rainfall intensity over time. They are one of the basic quantitative tools which hydrologists use to characterize a rain event. CALAMAR displays color-coded hyetographs for each basin within the study area. The user can select the basin and the time period.

Rainfall Intensity and Accumulation Maps
CALAMAR is a map based product that can display color-coded maps to show rainfall intensity in animated five-minute time steps and accumulated rainfall over an entire storm period. Maps can be over the entire study area or zoomed to individual hydrologic basins.

In CALAMAR's Real Time Mode Color-coded maps showing a one-hour forecast of rainfall accumulation across the service area are produced. Also available will be maps showing rainfall "indication" (similar to forecast, but with lesser degree of accuracy) for two and three hours in the future.

Tabular Data
CALAMAR outputs a variety of data including:

• Rainfall intensity in 5 minute steps and accumulation for every basin and mini-basin in the study.

• Calculation of storm event return frequency (e.g. 100 yr. storm, 5 yr. storm, etc.).

Animated Displays
CALAMAR's animation feature allows the user to view, on-screen, the passage of a storm. Several viewing formats are available. The user can select a large-scale view of the storm to understand its make-up, direction of movement, location and duration of high intensity rain cells, etc. This gives an excellent general overview of the storm and an overview of the next hour's forecast rainfall pattern. When viewing the rainfall forecast map, the system displays the confidence level of the forecast.

The user can switch to a more localized view and watch the storm's passage over the study area. By selecting a particular drainage area and time period, CALAMAR will animate the storm's passage and the development of the basin's hyetograph.

» Back to Finding I/I

For questions about the I/I Control Program Web site, please contact Maryann Petrocelli at 206-263-7321 or maryann.petrocelli@kingcounty.gov.

Department of Natural Resources and Parks
Wastewater Treatment Division

Updated: Jan. 15, 2008

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