During a flood, advance warning is the key to reducing damage and ensuring safety. However, conventional stream gauges— which are currently utilized to monitor rivers and predict upcoming flood conditions—can be costly and labor-intensive to maintain. In addition, gauges are often washed away during floods, resulting in a valuable piece of equipment being lost.
Researchers at the NOAA National Severe Storms Laboratory are working to improve streamflow monitoring with the Automated Non-Contact Hydrologic Observations in Rivers (ANCHOR) project.
The project is focused on three non-contact technologies to improve the observational and monitoring capabilities in rivers: Streamflow Radar, Scanning Lidar and Interferometric Stream Radar (ISRad). The streamflow radar portion of the project is currently the most robust, and 14 sites throughout the United States are already being installed with remote sensors that use Doppler radar to measure speed, depth, and flow rates in streams. Installations will take place through 2017 with results expected in early- to mid-2018.
This technology, used in combination with text alerts and notifications, has the potential to significantly impact water resource management practices and help reduce the damage and injury that occurs due to flooding.
To learn more about the project, R&D Magazine spoke with ANCHOR’s principal investigator Jonathan J. Gourley, research hydrologist with the NOAA National Severe Storms Laboratory.
R&D Magazine: What is ANCHOR project’s goal?
Gourley: I see a revolution, or at least an evolution, needed in hydrology in terms of observation methods. When I first entered the field of hydrology, people were still talking about basin-wide rainfall. If you have a study basin, you may have a couple of rain gauges in it and then the rainfall is typically measured by just looking at a time series of the average rainfall in the basin. With my experience in weather radar, this did not make any sense at all. We know there is rainfall that has spatial variability over this basin, and we can see that with weather radar. I had seen a similar thing happening in other hydrologic observations including soil moisture, the depth to the water table, and streamflow.
Streamflow is another variable that has been measured with a conventional gauge, which would be analogous to a rain gauge. Stream gauges have been around for decades. It occurred to us that, perhaps we can use some remove sensing technologies to estimate properties of rivers that would be interesting and improve, not only our knowledge and our research base, but that we could incorporate into models and do a better job of forecasting the streamflow.
R&D Magazine: What are the biggest benefits of using remote-sensing technology for stream flow measurement over conventional gauges?
Gourley: We have a project that has enabled us to buy an off-the-shelf commercial sensor that can provide us with two pieces of information using radar technologies. One of them is the stage of the river, which is the height or depth of the water. The second piece of information is the velocity of the surface.
The benefit of it is that the sensor is not in contact with the water. A conventional stream gauge uses either a stilling well with a floating device in there, or it uses what is called pressure transducer. That is where you have a little tube going into the water and then it pressurizes that, and is basically able to tease out what the depth of the water is. However, the instrument is in contact with the water, so what happens often, is when you have a big flood your instrument is gone. The advantage of the remove-sensing technologies is that they can be placed above the river so they are not lost. In addition, in today’s world with miniaturization, we can start thinking about putting them on drones and flying them around and then we can start getting the real distribution of the velocity of the river as we go up and down. These are ways of getting much more detail instead of just a point observation.
Another benefit is the cost. The sensors that we have out right now are about the same cost as what it takes to purchase and install a conventional stream gauge. The biggest difference comes in the operation and maintenance of a conventional stream gauge. The reason for this is that the typical stream gauge is not measuring velocity, but it is measuring a proxy for the stage of the river. Hydrological technicians for the USGS must visit each site several times a year under various conditions and they have to develop what is called a rating curve. A rating curve is a simple relationship between the depth of the water and the measured discharge. This would be the flow rate of the water measured in cubic feet per second. Basically, the technicians must go out there and measure the discharge manually, in the water, using instruments, several times throughout the year to update the rating curve. The stream gauge is measuring the stage every 15 minutes, so they use that rating curve as a look-up table, and say, ‘ok I have a river stage of eight feet’ and then use the table to provide the discharge estimate. The upkeep of that rating curve is very expensive because you are paying for labor for people to go out and take these measurements on a frequent basis.
In our case with the remove-sensing system, when you go out there and leave the instrument you have discharge immediately; you don’t need to go and establish their rating curve and keep updating it. That is the big advantage there.
R&D Magazine: How does the remote-sensing radar system measure velocity?
Gourley: The radar is pointing at an angle that is not straight down; it is either looking upstream a little bit, or downstream a little bit. This is a Doppler radar, so it is using Doppler principle, and from this, it is actually seeing tiny little ripples on the top of the surface of the water that are moving with the surface velocity. It is able to detect those and then use Doppler principle to figure out what the velocity is, moving towards or away from the radar.
R&D Magazine: These radar sensors are currently deployed at 14 sites. How were those locations selected?
Gourley: We had several criteria that went into that decision-making process, and we are still finding sites. We have a couple of sites where our sensors are co-located with existing conventional instruments for comparison purposes. That is something that we need to do in order to justify the validity of the instruments.
We also try to find areas that are known flash flooding areas that are not already gauged by conventional stream gauges, which are typically operated by the United States Geologic Survey. We work with a number of different local constituents, from weather services, to states, to universities, and try to find places that are repeat-offenders for flash floods. Typically, these systems are designed for smaller, headwater, even urban fast-responding catchments. The reason for that is that the bigger river systems like the Mississippi, the Ohio, the Colorado, are generally already pretty well gauged with convention stream gauges. We don’t want to duplicate too many efforts. For the most part, we are trying to find places that are not already monitored.
R&D Magazine: Who can access the information from these sensors?
Gourley: They are all transmitted in real-time and uploaded and accessible to the public. For each of the sites, we work with the local stakeholders there and establish thresholds. If the stream velocity exceeds certain thresholds, and they want to know when this happens, we can program in their cell phone number and then they get a notification as to when those thresholds are exceeded. At that time, it also increases the frequency at which the velocity is measured and the data is transmitted. So it adapts to the hydrologic conditions.
R&D Magazine: Why is it so important to accurately monitor the velocity of streams?
Gourley: I can provide you an example of the importance of this. Our first site was in Falls Creek, Oklahoma, near Falls Creek camp, an area that has a lot of visitors. We set up our thresholds and within two months of having installed the instrumentation we had severe weather in the state. My cell phone starts going off with the information about exceeding the thresholds in Falls Creek. I had my laptop on me and so I started looking at other products— rainfall products, flash flood prediction products—to make sure it wasn’t a false alarm. Sure enough they were getting heavy rainfall and this was the real thing. I texted our contact down there—the local stakeholder that is in charge of monitoring the conditions and making sure the campers are safe—and let him know that the weather conditions were deteriorating and that we were starting to get alerts from our stream radar system.
One thing that was interesting that we noted, is that the velocity of the river increased at least one hour prior to when we started to see the increase in the stage of the river. That gave them an hour heads up. We were starting to see the velocity increase and that meant that it was likely that the rise of the river would follow, which could result in the river coming up out of the banks and doing some damage. The instrumentation was upstream from the camp and they had a heads up. We were texting back and forth throughout the entire weather event, and the last text he sent me was, ‘all is well here, thank you.’ So, that was very successful that we had some early alerts, and were able to give them some information to respond. I can envision a number of areas elsewhere where this would be useful.
This interview has been edited for length and clarity.