Bioretention Research

Bioretention cells, also known as raingardens, have been identified as cost effective stormwater management tools. Generally, bioretention cells are shallow excavated or natural depressions designed to filter and store stormwater.

The Great Lakes are a national and international treasure. They contain 20% of the world’s surface freshwater, supply drinking water to 42 million people, and are the center of the region’s economy and cultural diversity. They generate $4.5 billion in sport fishery, $6.5 billion from fishing, in the eight Great Lake states. The increase in urbanization and has lead to an increase in polluted stormwater reaching the Great Lakes. In addition, the increase in urbanization has decreased stormwater recharge and lag time, which have been identified as a major contributor to flooding and deterioration of streams and rivers. This increase in runoff, decreases the ability of surface water to infiltrate and recharge the water table. This leads to a decrease in groundwater, which may negatively impact streams that rely on groundwater for a source of supply.

The negative impacts previously listed have lead to an increase in water quality and quantity regulations. To address the numerous stormwater management issues, innovative stormwater techniques have been developed and implemented internationally. A stormwater technique that has been identified as a cost effective best management practice (BMP) is the bioretention cell. This website is dedicated to providing research results and determining the effectiveness of bioretention cells for stormwater management for both water quality and quantity.

Publications, Reports and Presentations

Equipment

Rain Gauge

One rain gauge was ordered and installed near Site A. The rain gauge operates utilizing a tipping rainfall collecting bucket. The collector consists of a black-anodized aluminum collector ring with knife edge and a funnel that diverts water to a tipping bucket mechanism. The bucket is designed that for every .01 inch of rainfall the bucket tips. The bucket tips are then detected with a magnet that is attached to the bottom of the bucket and actuates a magnetic switch. The switch is connected to a HOBO data logger where the rain is recorded. The recorded rainfall is then discharged through a small opening in the bottom of the rain gauge. It is suggested that the rain gauge be cleaned periodically due to accumulation of bugs, dirt, etc. The rain gauge is accurate to ±1 percent, operating temperature range +32 Fahrenheit to 125 Fahrenheit.

HOBO Weather Station

One Weather station and two HOBO Weather Station data loggers were implemented. The data loggers include ten sensor connection ports, internal and external communications port. The data loggers run on four AA batteries, and the life of the batteries are dependent on the time interval of data sampling and collection, number of sensors, battery type and operating environment. This project utilized rechargeable batteries and the data loggers were programmed for 1 minute data sampling and 15 minute data collection.

Temperature Sensors

Five 12-Bit Temperature Smart Sensors are currently collecting temperature data. There are two in each cell at depths of 12 inches and 30 inches and one at the weather station collecting air temperature. The smart sensors have a plug-in modular connector that allows it to be added easily to the HOBO Weather Station. The sensors measurement range is from -8 to 212 degrees Fahrenheit (-40 degrees Celcius to +100 degrees Celcius), with an accuracy of ±2 degrees Celcius to -36 degrees Celcius, and resolution of less than 0.03 degrees Celcius to to less than 0.054 degrees Celcius.

Soil Moisture Sensors

Ten Soil Moisture Smart Sensors, five in each cell ranging in depth from 6 inches to 30 inches are currently collecting soil moisture data. Each of the Soil Moisture Smart Sensors provide accurate readings for soil between 32 to 122 degrees Fahrenheit (0 and +50 degrees Celcius), maintain integrity up to -8 degrees Fahrenheit (-40 degrees Celcius), and may be left in the ground year-round for permanent installations. The sensors do not require regular maintenance and come pre-calibrated for most soil types. The soil moisture sensor measures the dielectric constant of soil in order to determine its volumetric water content. The dielectric constant of water is much higher than that of air or soil minerals, which makes it a sensitive measure of the water content. A value of 0 to .1 m³/m³ indicates oven dry to dry soil respectively. Values of .3 to .4 m³/m³ normally indicates a wet to saturated soil. Values outside the 0.0 to .4 m³/m³ may be a sign that the sensor is not working properly.

HS Flume

Plasti Fab HS Flumes were utilized for this project to collect discharge from the underdrains at the bottom of the cells. The flumes were installed in the catchbasins located within the each of the cells. Due to catchbasin size constraints a .4 HS Flume utilized in at Cell A. Cell B utilized a .6 HS Flume. The .4 HS Flume is designed for a flow range of 1 gpm to 30 gpm, and the .6 HS Flume is designed for 1 gpm to 80 gpm. The flumes have flat bottoms and were installed level with the approach section and to allow free flow at the end.

Water Quality Sampler

The third piece of equipment ordered included two Teledyne ISCO GLS Compact Water Quality samplers. The samplers are compact portable that were designed for easy insertion and removal from manholes. They are utilized for stormwater run-off, combined sewer over flow, sanitary sewer evaluations, non-point source sampling and biomonitoring. For this project two wooden boxes were constructed, for weather protection and security purposes, and the samplers were placed within these. The samplers may be set up to sample based on time intervals or flow rates, and may be run separately or in conjunction with acceptable flowmeters. The samplers were calibrated utilizing procedures outlined within the GLS Compact Sampler manual.

Flowmeter

Two Teledyne ISCO 4230 FlowMeters were installed and programmed. The 4230 Flowmeter utilizes the bubbler method of level measurement. The bubbler system uses a small compress or pump to pump air into a reservoir. This air is released slowly by a needle valve into a bubble line, a length of small diameter flexible tubing. The other end of the tubing is submerged within the flow stream. Within the flowmeter the tubing is also connected to a differential pressure transducer. Air is slowly released into the tubing and as pressure builds the bubble is forced out in the flow. The amount of pressure to counteract the hydrostatic pressure is converted into the level of flow within the flume by the pressure transducer. The 4230 utilizes Flowlink software for data retrieval and storage. The 4230 is capable of storing over 40,000 data readings. The Flowmeter has capabilities of connecting to a sampler, raingauge, and modem.

Data

Continuous temperature, soil moisture, rainfall data is being collected at both Bioretention Cell A and Bioretention Cell B. The links below, Bioretention Cell A and Bioretention Cell B, include all data that has been collected thus far and is presented in a power point format. The data is collected from the data logger through a usb/com port and downloaded in to Hoboware Pro. The flow data is collected via usb port and is imported into Flowlink software. Due to the varying equipment companies and limited compatibility of soil temperature and moisture, rainfall, and discharge data, all data is exported to excel where it is then sorted and input into graphs to show the temporal impacts of each parameter.