Mystery of the Month - April

There are definitely some essential tools of the trade for our Water Quality team's variable work. There are at least three visible in the photo above (hint: the grey device is not a GPS). Think you know?


Answers: A Sonde, the Multi-parameter Display System that translates data from the Sonde, and a Jon boat! If you answered hats, motors, water, sunglasses, sunscreen and nearby personal floatation devices, you are also correct, but let's talk a little more about the technical side of things!


RWMWD monitors many different sites and bodies of water throughout our District. 


Lakes, streams, ponds, rain gardens, tree trenches and green roofs are just a few of things we monitor. Depending on the site, there are a whole bunch of different parameters we try to look at to help determine what is going on. It could be something as simple as finding the depth of water in a rain garden throughout a storm event or as complex as figuring out concentrations of dissolved oxygen, conductivity or heavy metals in storm water to name a few. 

A wide variety of District projects, studies, and sites requires a wide variety of equipment and instrumentation. Below is a brief summary of some of the equipment the Water Quality program uses around the District.

Orpheus Mini - This is a pressure transducer used to monitor water levels at our office site as well at water levels in the tree trenches at Maplewood Mall. There are really two parts to this piece of equipment: 1 – the pressure transducer that actually sits in the water itself and 2- the data logger which is the “brains” and is where all the programing is done. The data logger stores the information gathered from the pressure transducer.

Thalimedes - This is a weight, bobber, and pulley system used to measure water levels in rain gardens. It helps calculate how fast rain gardens drain. These units are generally placed in a protected metal or PVC tube that lets water in. As the rain garden fills with water it will raise the yellow float. That level is then recorded in the data logger. As the water soaks into the ground, the yellow float will lower. The amount it goes down over time is an important indicator of how 'healthy' a rain garden is.

ISCO 6700 series samplers

These are the District's water quality storm samplers of choice. These samplers are very reliable and can have a variety of sensors that can be “plugged” in depending on what we want to measure on the site. Generally, RWMWD uses two types of sensors: 1- 750 Area Velocity modules and 2- 730 Bubblers modules. Those two modules are the next items on our list.

 

750 Area Velocity modules – The District uses this type of probe/sensor in all of its monitored storm water pipes. This probe measures the average velocity in the stream flow though ‘patented’ Doppler technology. There is also a pressure transducer that can measure the depth of water. The ISCO 6700 series sampler then calculates the flow based on pipe size, water level and water velocity.

730 Bubblers modules – RWMWD uses a bubbler set-up in steams, holding ponds or in areas that always hold some level of water. Within the 730, there is an internal air compressor that forces air through a ‘bubble line’ (think aquarium hose) that is placed and anchored in the water. By measuring the pressure needed to force air bubbles out of the line, the ISCO 6700 sampler can calculate the water level.

Secchi Disk – This tool measures water clarity in lakes and ponds. This is done by lowering the secchi disk into the water column until it cannot be seen. We then raise the secchi disk so it can just barely be seen in the water. That depth is then recorded and a measurement of water clarity has been taken.

Transparency Tube – Using the same basic principal as the secchi disk, this device is used to measure water clarity in streams/creeks. First, staff takes a sample of water and fills a 1-meter clear tube with a small secchi disk attached to a string sitting at the bottom. Then, looking down into the tube, the string is pulled up until we are able to see the secchi within the tube. Some models (like the one pictured) has a fixed secchi at the bottom and the water is released through a tube until the secchi is visible. The numbers on the outside of the tube are then used to record the clarity.

Van-Dorn – The Van-Dorn is the ideal piece of equipment for obtaining water samples within the water column of deeper lakes. These devices are able to collect a water sample at whatever depth we need by using a trap-door-like system. We specifically use the Van-Dorn to grab our lake and pond bottom samples as well as samples directly above and below the thermocline (the depth at which the warmer and cooler waters meet).

0-2m Composite Rod – This hollow PVC tube is exactly two meters long and is used to take samples of the top 2 meters of water in our lakes and ponds. The tube is lowered into the water vertically, capped off at the top, then quickly brought out of the water and into a container. This works on the same principle as when you put your thumb over a straw to move your beverage from a glass to another location. Parents with kids and people who are former kids have likely experimented with this physics principle.

YSI 600XLM Sonde - The Sonde is arguably the most important piece of equipment that the Water Quality Program has (and the most expensive). There is a wide variety of sensors that can be installed for nearly instantaneous reading and results. They include: dissolved oxygen, temperature, conductivity, specific conductivity, salinity, depth, pH, and total dissolved solids just to name a few.  

YSI 650 MDS (Multi-parameter Display System) - This is the display and data logger for the 600XLM Sonde. Here we are able to program sites and store many points of data from multiple lakes and multiple locations.

Jon Boat – This boat is used for all lake sampling, aquatic plant (macrophyte) surveys, shoreline surveys, and installation of staff gauges and lake level stations. We use a jon boat for anything done on the larger bodies of water in the District.

Canoe – Our canoe is used for all pond samplings or any sampling that requires being on a body of water that our jon boat cannot be used.

Write in the Rain Notebooks - These special notebooks are made for folks like us who tend to be working outside more if it does rain. They allow staff to write notes, measurements, or data results in almost any condition.

If you can imagine, this list contains just a few of the many tools that our Water Quality staff use to monitor our lakes, ponds, streams, rain gardens, Best Management Practices (BMPs) and more. We're glad to have Eric, Dave, and Wyatt, our summer intern, on staff to manage and maintain all of this equipment and data!