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REMOTE MONITORING OF GREEN STORMWATER
INFRASTRUCTURE USING SOIL MOISTURE SENSORS
India Harris and Cyndee Gruden
Lake Erie Center and Department of Environmental Sciences, University of Toledo
Methods
UT Weather Station Data
The dielectric moisture sensor measures soil moisture, and
the data is collected using a portable microstation logger
which operates at defined intervals.
Precipitation varies greatly by geographic location. The UT
Weather Station located near the tree filter records the rain,
temperature, soil moisture, and other various measurements.
Data loggers collect information every minute and can be
accessed remotely via the Internet.
• ECH2O Soil Moisture Sensor
• HOBO Micro Station Data Logger
Soil moisture content can be calculated using the gravimetric
or the volumetric method. The sensor measures volumetric
moisture.
Volumetric water content, θ, is related to
gravimetric water content, w, by a ratio of the bulk density, p,
of the soil (1 to 1.6 g/cm3) to water (1 g/cm3) :
0.5
UT Weather Station
Weather Station Data
θ=w(ps\pw)
Site Description
The tree filter was installed at (UT) adjacent to the law school
parking lot to improve the water quality of the Ottawa River by
collecting and filtering contaminants from parking lot runoff
and to raise awareness about green stormwater management
alternatives.
The
tree
filter
captures water from
four catch basins in
Lot 12 (0.8 acres)
near
the
Law
School. During a
1/4-inch rain, over
5,000 gallons of
runoff are conveyed
3D figure of the tree filter components
The Tree Filter
to the tree filter.
Lot 12 Location of Tree Filter
Results and Discussion
Lab Experiment
Installed Moisture Sensor
The range of volumetric water content (VWC) is dependent
on the porosity and organic content of the soils tested. VWC
is defined as the fraction of the total volume of soil that is
occupied by water. The sensor measures the VWC in the
liter of soil surrounding the sensor.
Laboratory experiments were carried out to simulate clogging
that is expected to occur over time in the field. The soil
moisture measured for the clogged sample was consistently
higher (up to 10%) than the unclogged sample. The soil
moisture of the clogged sample was initially 15% as compared
to the unclogged sample which was 5%. As the moisture
content increased during the experiment, the difference
between the clogged and unclogged samples decreased. The
experimented soils we used are saturated at 43% (Vw/Vs).
This data will be used to help interpret field data to indicate
clogging or flooding of the tree filter.
In the field, the weather station and installed sensor were
continuously collecting data during and between rain events.
For this study, rain data was extracted from a week in June
(22nd to 29th). During this time, a total of 4.11 inches of rain
fell. There were three major rain events.
Sensor #2
0.4
Clogged and Unclogged Experiment and Data
0.03
0.025
0.02
0.3
0.015
0.2
0
Section View of
Tree Filter
0.035
Rain, in
0.01
0.005
0
UT Weather Station Data
Conclusion
Soil moisture sensors could be used to remotely monitor
green stormwater infrastructure. Water concentration itself is
often a parameter of interest, especially in infrastructure that
includes plants as part of the treatment process. The amount
and the availability of water in the soil are important. At the
same time, the soil moisture can indicate whether the system
is functioning properly and may likely provide an indication of
the need for infrastructure maintenance.
Acknowledgements
Experimental Procedure:
In the laboratory experiment, soil was placed in two reactors
made from pieces of screened pvc pipe to allow free
draining. Soil (500g dry weight) was placed in each reactor.
Soil in one reactor was covered with debris from the tree
filter to imitate clogging that may occur. The sensor was
inserted in the middle of the soil column and launched to
begin taking readings. A total amount of 250 mL of tap water
was poured over each reactor, 50 mL every 2 minutes.
Water continuously drained through the reactors. After 10
minutes of output, the data was extracted from the logger
using HOBOware software and transferred to Excel to begin
manipulating the output to place into a table.
Sensor #1
0.1
https://www.hobolink.com/p/aa90e60bbfbbb7ef63a9da89c178cc8e
The goal of this research was to determine if soil
moisture sensors can be used as a tool to remotely
determine if green stormwater infrastructure is
functioning properly and whether or not maintenance is
required to restore normal operation.
UT Weather Station
0.6
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Green stormwater infrastructure is being used to reduce the
water quality impacts of urbanization. Green infrastructure
can treat the contaminants carried by runoff during large rain
events and minimize the release of untreated stormwater into
the local waterways. To work well, green infrastructure has to
be properly maintained. It can be difficult to predict when
maintenance is needed. In this project, we used a dielectric
soil moisture sensor (ECH2O 10HS from Decagon) to
determine if the tree filter is working properly. Data loggers
collected information every minute and were accessed
remotely via the Internet. If the tree filter is working, water
infiltrates in a consistent pattern characterized by a drop to
background moisture levels (15% to 25%) when the rain
stops. If it is clogged or there is some sort of obstruction, soil
moisture climbs and remains higher than an unclogged filter
until it suddenly drops (often before the rain stops) from
finding a preferential pathway such as a crack in the soil.
Moisture Content, m^3/m^3
Introduction
Our field data shows that soil moisture (VMC) changes in
response to rain. The soil moisture levels drop from a high of
about 50% to just above background levels (approx 20%)
within minutes (<15 minutes). This is difficult to simulate in the
lab with small reactors as generating a realistic field scenario
would take a great volume of soil and clogging occurs over an
extended period of time. If the filter was clogged you would
expect the background soil moisture levels to be higher than
usual since the debris insulates soil moisture from
evaporation and contains more organic to hold more water. If
the moisture content was initially higher as compared to
“normal” levels and did not return to background levels after a
rain event within a reasonable time frame, this may indicate
clogging and that maintenance is need at the tree filter.
NSF REU Program #DBI1461124 to The University of
Toledo’s Lake Erie Center,
“Undergraduate Research and
Mentoring- Using the Lake Erie
Sensor Network to Study LandLake Ecological Linkages”.
The difference in soil moisture content (VMC) can be
explained by the presence of the debris. The initial moisture
was higher than expected. The debris collected from the field
was not completely dry, which added moisture to our sample
during the experiment and maintained the moisture at a
higher value during the experiment. The experimented soils
we used are saturated at 43% (VMC). It is anticipated that
the unclogged soils will also return quickly to background
moisture levels while the clogged soils will not.
www.utoledo.edu/nsm/lec/