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.