Lake Management Plan

go to PGOLID main pageChapter 1 includes an introduction and abstract
Chapter 2 includes the goals of PGOLID
Chapter 3 history covers geological formation to current district projects
Chapter 4 covers watershed characteristics of most of northwest Minnesota
Chapter 5 covers the main watershed around the Pelican Lakes
Chapter 6 covers the minor watersheds that surround Pelican Lake
Chapter 7 describes the types of data collected and why
Chapter 8 reports the data and water quality of inlets and outlets to Pelican Lake
Chapter 9 reports the water quality data for the Pelican Lakes

Chapter 10
Chapter 11 Safety and Buoys

 

Questions?
PGOLID Water Resource Coordinator
218-846-1465, email

Chapter 7: Data Collection and Water Quality Indicators

7.1 Flow and Concentration

Data that comes back from the lab is usually given in a concentration. A concentration is unit per volume. Most concentrations are in milliliters per liter (volume/volume) or milligrams per liter (mass/volume). The volume is the amount of water tested, and the smaller volume, or mass is the amount of substance found in the overall volume.

Concentration can be compared to other lakes and rivers to determine there relative health. There are also known critical concentration levels that if reached certain impacts can occur such as algae growth and fish deaths. These concentrations are known from experimentation and experience. There is always a direct correlation to concentration levels and the quality of the water.

Flow is the amount of moving water in a stream or river. It is the velocity of the water multiplied by the cross sectional area of the river and is given in units of volume per time. Velocity is measured by using a flow meter. The flow meter is a small propeller that spins in moving water. The number of turns the propeller makes in a given time is used to calculate the average velocity of the water. The cross sectional area is measured or calculated. Usually it is measured at a culvert because measurements can be taken and calculated much easer and thus reduce error.

Flow is important for quantifying the amounts of substance flowing in a river. By multiplying the Flow by the Concentration we can quantify the mass or volume of substance, this is called loading and is given in units of unit (mass, volume) per time (second, day, year). Typically it is converted into gallons per day or lbs per day. Rivers that flow into lakes can greatly influence its quality. Calculating the loading identifies the greatest contributor of pollutants. For example a large river with low concentrations may be impacting the lake less than a small stream with high concentrations.

Programs were built to calculate the flow and loading for each of the sampling sites around Pelican Lake using Microsoft Excel.

Flow is calculated by taking the sums of the water velocities multiplied by their corresponding water cross sectional areas.

There are different calculators for each type of site shown in the pdf below. There are calculators for bridges and 5 different culverts. The calculator type also depends on the sediment. Static sediment is sediment that does not move such as rock or compact gravel. Dynamic sediment is sediment that is moving thus changing the waters cross sectional area, for example, sand.

Click here to download a pdf explaining site calculations (200 KB)

Next page: Chapter 7.2 Nutrients

 
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