Monitoring for Your Objective

Stormwater management requires an understanding of the volume moving across the landscape and through municipal infrastructure.

Monitoring for Your Objective

Interested in Stormwater?

Get Stormwater articles, news and videos right in your inbox! Sign up now.

Stormwater + Get Alerts

Stormwater monitoring can be challenging. With what seems like endless variables and situations impacting data, documenting and calculating stormwater isn’t as simple as putting a rain gauge on your garden post.

In a recent webinar presented by Xylem, Dr. Stephanie Smith discussed these challenges and provided examples of monitoring projects in different scenarios. She provided tips that can help you set up a successful monitoring program.

Whether it falls on prairie land, wooded forests, airport runways or metropolitan rooftops, precipitation eventually runs into tributaries, rivers, lakes, streams and, ultimately, the ocean.

Monitoring the amount of water moving across landscapes and through our municipal infrastructure during a storm is an integral part of deciding how to manage stormwater. Data collected is used to support sewer system programs, for regulatory decisions, and to detect point source discharges as well as nonpoint source pollution.

Methods of monitoring

YSI, a Xylem brand, has had its hand in numerous studies involving stormwater in the U.S., and Smith highlights three successful monitoring programs, the first involving an oil refinery in Texas.

“Refineries, if you’ve ever been around one, you recognize they are like little cities,” Smith says. “They’re really big, lots of paved surfaces, lots of metal, things that water is just going to bounce off. But, of course, the things going on there are also not necessarily things you want running off into your waterways.”

It’s not uncommon for refineries to take monitoring into their own hands, measuring pollutant concentrations in runoff from their site. Many are even setting up monitoring systems in nearby rivers, streams and lakes to get more information on what from the plant reaches specific downstream locations. In this situation, the Texas refinery used a SonTek-IQ, a doppler instrument that measures volumetric flow. Data from that instrument is paired with a storm data logger and telemetry to give them a constant stream of cellular transmissions.

Data is sent to HydroSphere data management platform, allowing the refinery to constantly see river flow downstream. “By doing this, they are able to always keep track of what their discharges likely are, based on those early estimates just by measuring volumetric flow,” Smith says. “This is a very cost-efficient way to do long-term stormwater monitoring from a site like a refinery.”

The second example relates to hurricane monitoring and also takes place in Texas, where two regions are monitored by the Texas Commission on Environmental Quality through its Clean River Program. Many stakeholders engage in this program; in this case, the Environmental Institute of Houston. “They were doing monitoring on creeks in two regions in Texas, the San Jacinto-Brazos region and the Brazos-Colorado region,” Smith says.

Monitoring sites were set up in 2017, shortly before Hurricane Harvey hit Houston. They started with pre-installation research to better understand discharge in the specific sample creeks. They used SonTek’s FlowTracker2 and RiverSurveyor M9 to understand instantaneous discharge measurements. “This is called a passive sampling approach where they can basically have the M9 on a board and understand discharges as they occur across that creek in normal conditions,” Smith says.

They would measure the stage, or water level, and when pairing with discharge data, they created stage discharge relationships. To measure stage in a continuous manner, Amazon Bubblers, devices that constantly measure water level, were installed at each station. The team also used a storm data logger and Geostationary Operational Environmental Satellites for transmissions.

“They were using satellites,” Smith says. “They have the data going up to HydroSphere. They’re actually processing that data and putting it on their own website, so it is always available to the public.”

Another aspect is that the equipment was battery-powered; that is critically important, according to Smith. And not only was it battery powered, but also solar recharged.

During Hurricane Harvey, the level in the creeks where two of the stations were positioned rose 7 to 8 meters. They were able to use those stage measurements and the discharge relationships they had previously built to analyze potential pollution through each creek during that storm event.

The third case Smith highlights is the Terrebonne Levee in the Gulf Coast. After several years of substantial hurricanes, a citizen group formed and began working with the Delta Coast Consultants Group, a group that manually operates barge gates requiring the operator to know how to manage the flow through the gates.

“In the long run, they needed to always understand level, always understand flow, but they also wanted to see what was coming,” Smith says. “Weather monitoring and understanding the rain patterns in the region was really important to them. But they needed to know more than just the national weather service forecast.”

The group chose a Nile Radar noncontact water level sensor instead of a submersible sensor so it could not get swept away by the current created from barges going through the gates. Because of the vast volume of water being measured, they knew water level changes would be small. They placed a SonTek Side-Looker combined with radar at several gate locations to get accurate readings on the subtle changes.

An extremely important aspect of this monitoring technique was the use of redundant power sources and telemetry. Both satellite and cellular telemetry was used at each site, allowing them to persist with measurements through several severe storms since installation.

Case commonalities

Each case discussed in the webinar was a successful and useful example of stormwater monitoring. There are several factors that made them effective, and one crucial aspect was that each case had something definite to measure.

“You have to start with what your real objective is before you start stormwater monitoring,” Smith says. Without a clear goal, it’s easy to just record measurements that never amount to useful data.

Another thing these programs had in common was redundancy in power and telemetry. Backup in these areas will come in handy. It’s often during storm events that collected data is most valuable, which is also when the first line of power and telemetry have a higher chance of failure.

Smith says that having real-time visibility to data recorded was vital, especially during times of storms when manual data collection is near impossible. “That is why telemetry was so important. You’re trying to get away from the storm in many cases, but you need to be able to see the data coming in and have a reliable system for delivering that data even when power is lost in a region.”

Developing a monitoring program

According to Smith, step one in creating a stormwater monitoring system is to start with the objectives. Before doing anything else, determine exactly what you want to measure and why.

“Don’t start with sensors, start with the objective,” she says. “For the levee, their objective was to know how to manage those barge gates and what information they need to know to do that. For the oil refinery, their objective was completely different. They wanted to really understand what their discharges were related to their permitting levels. Completely different, and you have to take a different approach.”

The key is to think about what you’re trying to achieve, and the types of sensors and equipment needed will come from answering that question. Once sensor types are chosen, think of the environment and specific site to refine the sensors and chose the exact model that best fits the scenario.

Once the objective is set and sensors are chosen, it’s time to develop a sampling routine. Decide when samples need to be collected and how often. This will determine whether manual collection is enough or if automated is necessary. Any objective that requires data collection during a storm event obviously favors automated samplers.

Along with choosing the method of collection, this is the time to select the area where samples are to be taken. “This always is going to tie back to your objective and what it is you need to know,” Smith says. “You’re going to need some sort of a sampling program nine times out of 10 with stormwater monitoring. Now, if you’re monitoring just for flooding, that might not be necessary for you.”

The third step to defining your stormwater monitoring system, according to Smith, is to define the notification requirements. This comes down to deciding exactly what you want to know and when you want to know it.

“If you’re monitoring for a pollutant directly in the water, maybe the only time you want to know something is when you’ve exceeded some limit,” she says. “This is also highly relevant for National Pollutant Discharge Elimination System permitting. So, define when, where and how you want to get your notifications.”

Once alerts are decided, move on to determining power requirements. This is where Smith says a lot of people make mistakes. Between all the samplers and different types of sensors, the power load needed is crucial to understand and acknowledge. “Doppler sensors always have to have hard power to them,” Smith says. “When we start talking about that, you really need to understand the load requirements of those sensors and how much power you have to set that station up with. The ideal situation is to have redundant power.”

She goes on to say that many systems are set up with main power and a battery backup. Some even have dual batteries to give another line of power during storms if main power is lost. Adding solar charging modules to the batteries is another line of power security that is easy to achieve. “I never recommend having single-layer power for a stormwater monitoring system in particular,” she says.

And finally, Smith says to secure all necessary equipment. At this point the objective is clear and equipment has been purchased. Now it’s time to protect the investment. Though it may seem obvious, it can’t be stressed enough to properly fasten all sensor and measuring devices to ensure they remain in place.

“You have to secure that equipment so it’s not going to get washed away during a storm,” Smith says. “But you also want to make sure there’s good sun if you’re using solar recharging for the power system. With things like a radar, you really need to secure it well on a bridge or some other type of structure that’s not going to get blown away.”

It pays to consider human tampering as well, especially in heavily populated areas where sensors are easily accessible. Make sure devices that are available to vandalism are locked and protected.

These specific examples of successful stormwater monitoring provide a framework on which to base future monitoring programs. The ideals behind the strategies are what should stick and will prove helpful for planning stormwater monitoring, whether downstream of a refinery or in municipal collection systems.

Stormwater events can wreak havoc on sanitary sewer systems and cause severe infrastructure damage. Collecting accurate data is vital to designing systems that can handle stormwater surges, limiting flooding, erosion and sewer system overflows. 


Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.