Gauging rain in an era of atmospheric rivers

The challenge

In the early 2000’s, the Ventura County Public Works Department was intent on resolving significant data loss in its rainfall measurement network. Clogged rain gauges and an unsatisfactory tipping mechanism (pivots) in gauges required excessive maintenance to fix issues and keep the 1 mm gauges in calibration. In particular, bird droppings and pollen were clogging funnels.

Poor equipment performance was becoming costly. In addition to lost data, repairs and constantly calibration was consuming limited resources.

The staff sought a low-maintenance, high-accuracy, high-resolution rain gauge to measure rainfall at 0.01 inch. They wanted reliable monitoring data to warn people of flood risk.

Key Challenges

• Funnel clogging
• Ineffective tipping mechanism
• Gauges required frequently calibration
• High maintenance costs, in terms of both time and money

The solution

The County selected the KISTERS TB3 in 2002 due to its unique design, robust construction, reliable data collection with long-term stable calibration. After careful consideration, the following key features resolved the issues:

• A stainless steel finger filter substantially reduces clogging.
• The tipping bucket mechanism, the low wear / low friction sapphire pivot, is superior to pivots in their legacy gauges.
• A flow control siphon improved accuracy across a wide range of rainfall intensities.

By 2005, a big push to immediately replace all the troubled sites with the inferior rainfall measurement devices was made. Rain gauges on other less-problematic sites were eventually replaced with the TB3.

The network currently features 75 TB3 tipping bucket rain gauges. The Ventura County Public Works Department intends to maintain the model as its frontline instrument.

The benefits

Substantial improvement in data quantity and quality — Ventura & adjacent counties

Widespread adoption of the TB3 tipping bucket rain gauge resolved the data loss issue due to clogging, poor tipping bucket mechanism, high maintenance demands. Since the incorporation of the TB3 we have experienced substantial improvement in data quantity and quality. Since 2005 the TB3 has been the backbone of the Ventura County Rainfall Monitoring Network — becoming the go-to gauge for the county.

Ventura is not the only consumer of this information. Other nearby agencies including Los Angeles, Santa Barbara, and San Luis Obispo counties observe the information and benefit. In fact, during the devastating 2018 Montecito mudslide in Santa Barbara County, many agencies looked to data provided by Ventura County’s monitoring network.

A minimum 20% reduction (savings) in labor-hours.

The reduction in labor and overall costs to maintain the rainfall measurement network was key. Resolving the problematic issues was a game changer. The substantial reduction in site visits to repair and maintain calibration freed up field technicians to focus on more pressing tasks. The long-term, stable calibration of the TB3 has recovered much time and effort.

Data loss prevention via dual reed switch

After some analysis, it was determined that a backup logging capability was needed to prevent data loss. Prior to the implementation of the new rain gauge, this was not possible.

The TB3 features a dual reed switch to connect one reed switch output to the KISTERS ML1 mini logger installed in the rain gauge and the other reed switch to a flood warning transmitter. The ML1 allowed the County to achieve its data redundancy objective.

Every TB3 gauge in the rainfall monitoring network is attached to a ML1 mini logger. The ML1 on every site officially records an instantaneous time stamp on every tip of the pivot. Moreover, the mini logger’s battery lasts a whole year, which is critical when visiting back country sites occurs.