Automating Crest Stage Gages with Continuous Monitoring Instruments

Crest stage gages are typically used to gather data from ephemeral streams or waterways that are subject to infrequent, but severe flooding. Increasingly, crest stage gages are becoming a cost-effective means of gathering peak flow data, which can then be used in a variety of applications, such as emergency planning, engineering design, and stormwater permitting.

The United States Geological Survey (USGS; 2006) describes the advantages of automated crest stage gages:

•Record date, time, and continuous data
•Measure multiple peak flow events between site visits
•Do not require field calibration
•Reduce site visits
•Offer user-selected recording time interval
•Integrate into real-time monitoring networks

The USGS (2006) cites equipment cost as the primary disadvantage of automated systems. However, by factoring in labour and fuel costs and the benefits of high-resolution data, automated systems offer very cost-effective monitoring solutions.

Choosing an Instrument for Use as a Crest Stage Gage

When selecting a level-measuring device, first choose an absolute (non-vented) sensor, such as the Level TROLL® 100 or Level TROLL® 200 instrument. A gauged (vented) sensor will flood if the peak flow elevation exceeds the height of the vent tube. The Level TROLL 100 is deployed on a suspension wire. Optionally, the Level TROLL 200 can be deployed on direct-read cable to access data without removing the instrument or to access data via telemetry. By using the Level TROLL 200, you will not need to re-survey the site or reset the level reference after downloading data.

You will also need a BaroTROLL® 100 instrument running concurrently with the Level TROLL instrument to compensate for barometric effects on the data, if required. Select a safe location near the Level TROLL where the BaroTROLL 100 will not be submerged during peak flow. Please visit www.in-situ.com to download a technical note on automating crest stage gages.