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Remote Water Level Monitoring - Nearly 5 in. of Rain in Under 24 hrs. WIU ENVIRONMENTAL SCIENCE AND THE QUAD CITIES CONSERVATION ALLIANCE WETLAND COMPLEX, East Moline, IL - PART 2

On March 28 and 29, 2020, we measured our first significant rainfall since installing two Micro RX2100 Water Level Stations (OnSet Corp.) at the Quad Cities Conservation Alliance's (QCCA's) wetland complex in East Moline, IL.

We're fortunate to have the support of the Moline Conservation Club who provided the funding for the instrumentation we use in this work and the QCCA who let us work at their site!

Site overview

The QCCA Wetland Complex in East Moline, IL, is approximately 65 Acres.

The lake is about 14.5 Acres, depending on the water level.

We were able to install one a the inlet and one in the lake. The third station will be installed at the outlet once COVID19-related social distancing measures are lifted.

The site has very little topographic relief - it's very flat.

The station at the lake was installed on a peninsula that allowed us to deploy the level sensor near the geometric center of the lake and collect atmospheric data that are representative of conditions on the property.

The station at the inlet was installed about 8 ft upstream from a footbridge. This channel has an almost rectangular cross section with a bankfull width and depth of 6 and 2.4 ft, respectively.

Water level Data

At 22:00 on March 27, rainfall was detected by the sensor located at the lake. In a little less than 20 hr., the water level in the lake rose by 0.1242 m (4.89 in.) to a maximum depth of 1.0391 m. It's also interesting to note that the 95% of the rise in water level occurred in just 9.5 hr.

So, why or how is this information useful?

We can estimate the volume of water added to the lake. This requires a little algebra and a few assumptions.

  • Let's assume that the lake has a fixed cross sectional area. That means the sides aren't sloped and the bottom is flat.
  • Let's also assume that water isn't being lost from the lake to recharge groundwater.
  • Likewise, we need to assume that there are no other large sources of water that aren't associated with the storm.
  • For the sake of completeness, we should also assume that any loss of water due to evaporation and evapotranspiration (water loss through plant respiration) are negligible.
  • If we rectangular box, the volume would be the area of the bottom multiplied by the height of the box.
  • The lake certainly isn't a rectangle, but we already know it's area (14.5 Ac = 631,620 sq. ft.)
  • The "height" in this case is the increase in water depth 4.89 in. (0.408 ft.)
  • This is a volume of ~258,000 cu. ft. or 1.93 million US gallons.

Let's put this volume of water into perspective. 258,000 cu. ft. or 1.93 million gallons of water correspond to ...

...enough water to fill a football field (including both end zones) with nearly 4.5 ft. of standing water ...
... or enough to fill 203 tanker trailers.
This volume of water has a mass of a little more than 16 million lbs. (7.3 million kg) or 8,000 US tons.

What about the water level station at the inlet?

Over the same time period, the water level station at the inlet recorded an increase in water depth of 0.1346 m. This is in close agreement with the value determined at the lake (0.1344 m).

A word about measurements of accumulated rainfall and the increase in water level ...

Over the duration of the storm, we measured an accumulated rainfall of 70.4 mm (2.77 in). This corresponded to only 57% of the 4.89 in. rise in water depth observed in the lake. The balance of the increase in water is likely due to surface runoff. In the future, it would be interesting to add a few wells to monitor the levels and movement of subsurface water - especially since the groundwater table is known to be very high at the site.

Why is this work important?

It might not look like it, but the QCCA Wetland Complex is an urban wetland. It's well known that wetlands help mitigate the effects of flooding in addition to providing habitat for wildlife and a natural place for people to encounter nature. The work we're doing will add valuable information on the ways in which this urban wetland functions. The best part is that we're able to monitor conditions at the site around the clock which wouldn't be possible without this new generation of remote sensors.

Created By
Roger Viadero
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