Spring flow and water quality in the Lake Wingra watershed

Nick Ballering, Professor Jean BahrDepartment of Geology and Geophysics, University of Wisconsin, Madison

Undergraduate Research Scholars Program

Abstract

The purpose was to determine the quantity and quality of spring water flowing

into Lake Wingra. We measured the flow of some springs with a dam-like device called a

weir. At other sites we took periodic flow measurements using a spinning mechanism

called a pygmy meter. We measured quality using a salinity meter and various chemical

tests. MG&E is planning to construct groundwater infiltration basins in the Lake Wingra

watershed, which may affect the amount of spring flow into the lake. Our results

established baseline measurements of spring flow, which will be compared to later

measurements in order to determine the recharge station’s effectiveness. In addition, we

determined how much the flow rates naturally fluctuate based on precipitation levels and

seasonal changes.

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Introduction

Lake Wingra is a located on Madison’s near west side. Water enters the lake from

direct precipitation, storm drain runoff, and from natural springs, and flows out through

Wingra Creek on the lake’s eastern edge. Spring flow is the preferred method of inflow,

because runoff carries pollutants from the streets into the lake. A strong spring flow is

also a sign of a healthy aquifer. Aquifers are important because they clean the water. A

study done in 19991 suggests that there may have been at least twelve springs at one time.

Changes to the land usage in the watershed have caused some of these springs to

disappear. As more surfaces are paved the rain cannot infiltrate into the water table, and

instead enters the lake through the storm sewers. While the 1999 study measured many

facets of the Lake Wingra watershed, they did not measure the spring flow directly

because of funding limitations, political barriers, and the difficulty of the task due to the

nature of the springs. The purpose of our project was to measure these springs.

There are eight springs that feed Lake Wingra directly. One large spring and at

least two smaller springs are located in the Arboretum, one is in the Nakoma Golf

Course, one is along Nakoma Rd. near a duck pond, two others are situated off of

Monroe Street near the Council Ring, and another is located on private property on

Woodrow Street. The outline of the Lake Wingra watershed and the locations of these

springs are shown in Figure 1.

Madison Gas and Electric (MG&E) is planning to build a new power plant. In

compensation for water used by the power plant they have proposed the construction of

infiltration basins near Odana Hills Golf Course. They will utilize underground trenches

to infuse captured runoff water into the water table. The groundwater is expected to

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migrate east, towards Lake Wingra. The Duck Pond and the Big Spring at the Arboretum

are expected to experience the largest effect.

The purpose of the study was to establish baseline measurements of the quantity

and quality of spring water flowing into Lake Wingra. When the infiltration basins are

constructed new measurements can be compared to this study’s data to determine the

effectiveness of the basins at increasing spring flow. We took periodic measurements

over the course of the study to determine how much the flow rates naturally fluctuate

based on precipitation levels and seasonal changes. Knowledge gained concerning these

natural fluctuations could help future researchers design their studies for measuring

spring flow.

Method

We measured spring water quality at all sites using a temperature probe, a

conductivity meter, and chemical tests. The conductivity meter measures the electric

potential in the water to determine the concentration of dissolved solids. We tested for

two different chemicals: nitrates and dissolved oxygen.

Measuring the magnitude of spring flow was more difficult. The optimal

technique uses a dam-like structure called a weir. Weirs are constructed from wood or

plastic and are situated across the width of a stream. They direct all of the flow through a

notch or trough cut in the top. One can easily determine the flow at any time by

measuring the height of the head water flowing through the notch. Unfortunately weirs

are difficult to construct and install, and they only work in relatively deep channels with

steep banks. At this point in the project we have only installed one weir: a 120° weir at

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the golf course. This weir is shown in Figure 2. The formula for calculating the flow

across a 120° weir is Flow = 2.50 H5/2, where flow is in ft3/s and H is the height of the

head in feet (Figure 3)2. Weirs will eventually be constructed at the Duck Pond spring,

the Council Ring Springs, and the Woodrow street spring. The other springs are not

suitable for weirs.

At the Arboretum and Duck Pond springs we used a pygmy meter. This device

involved a spinner on the end of a rod connected to earphones. We lowered the spinner

into the stream, and every time it went around we heard a clicking sound in the

earphones. Counting the number of clicks in a minute revealed the velocity of water at

that point. Figure 4 shows the pygmy meter in use. By measuring the depth of the stream

at various widths we divided a cross section of the stream into small rectangles. We

calculated the flow in each rectangle by multiplying the velocity of water in the rectangle

by its area. We found the total flow of the stream by summing the flows of all the

rectangles. We calculated flow in cubic feet per second. Figure 5 illustrates how a stream

bed is divided into rectangles.

We analyzed the data by plotting each of the measured traits over time for all

springs. These plots (Figures 6 through 10) illustrate the average flow rates and water

quality at various springs, as well as the degree of normal fluctuation.

Results

To establish baseline measurements for each trait we plotted the trait over time at

each spring location. The plotted traits included flow, temperature, nitrate concentration,

dissolved oxygen concentration, and conductivity. From these plots we can see overall

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trends and fluctuations of each trait at each spring. We can also see how much the springs

differ from each other with regard to each measured characteristic.

Flow measurements remained fairly constant as seen in Figure 6. The duck pond

flowed at .8 ft^3/s and the Arboretum spring flowed at approximately 1 ft^3/s. It ranged

up and down by .2 ft^3/s.

Temperature remained fairly constant for all springs at approximately 11°C with

the exception of the golf course, which varied greatly (Figure 7.)

Conductivity remained constant for each spring, but there were differences among

the springs. See Figure 8. The golf course had the highest conductivity with 1200 uS,

followed by the Upper Council Ring spring and the duck pond with 1000 uS, the

Arboretum with 900 uS, and the Boiling Council Ring spring with 800 uS.

The dissolved oxygen tests showed consistency at the Arboretum and both

Council Ring springs but more variable changes at the golf course and duck pond. See

Figure 9.

The nitrate tests were sporadic at every spring and showed no clear consistency or

trends. See Figure 10.

Discussion

Some spring characteristics remain very constant while others fluctuate greatly.

Flow, temperature, and conductivity remain fairly constant while dissolved oxygen and

nitrates varied a lot. It is well-known that regional groundwater is about 10°C all year,

which accurately fits our data. While temperature was almost the same for all springs, the

conductivity varied from one spring to the next, but remained constant over time. This

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suggests that the amount of dissolved solids represents a fundamental difference between

springs. We did not notice any long term trends for any of the traits.

The variable nature of some traits may be the result of difficulty in making

accurate measurements rather than an actual difference in the spring quality. For instance,

the golf course spring should have maintained a constant temperature like the other

springs, but it did not. The spring at the golf course is located at the bottom of a deep

pool so it is more difficult to measure it directly. The measured water was nearer to the

surface so the temperature readings from the golf course more closely resemble air

temperatures. The nitrate and dissolved oxygen concentrations seem to fluctuate more

than the other characteristics. The Boiling Council Ring spring was easiest to measure

directly because of its location. This spring shows the most consistent measurements

among all traits. Springs that could not be measured directly were not as consistent in

their results. This suggests some of the variations in dissolved oxygen may be due to

aeration in the spring pool, rather than changing characteristics of the actual spring water.

The large fluctuations in nitrate concentrations could be due to seasonal variations in

fertilizer applications in recharge areas.

The most important trait for this study is the flow. Unfortunately we still have yet

to find methods to measure flow at every spring. From the flow data at the Arboretum we

expect the flow to remain fairly constant over time, but to vary greatly among springs

because they are different sizes.

There is still much to be done with this study. The first priority is to establish

methods to obtain flow data from all of the springs. The weir at the golf course will be

finalized, and weirs will be constructed at the Council Ring springs, the Duck Pond, and

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the Woodrow street spring. At some springs we may use dilution gauging3 to measure the

flow. This process involves putting a known concentration of a tracer chemical into the

stream and then measuring the dilution that chemical downstream.

The results shown here represent data taken over only a few months. The study

will continue for several more months to determine any larger seasonal trends. Once this

is done we will have established only what springs do under normal circumstances. Once

MG&E constructs the infiltration basins this entire study will be repeated to determine

the effect that the basins had on spring, which is the ultimate goal of this project.

References

1. The Institute for Environmental Studies, The Water Resources Management Workshop, and the University of Wisconsin Madison; Lake Wingra Watershed: A New Management Approach; 1999.

2. Stevens; Water Resources Data Book,4th Edition; Leupold & Stevens, Inc.; 19873. Herschy, Reginald W; Streamflow Measurement: Second Edition; Elsevier

Applied Science Publishers Ltd.; 1995.

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Arboretum Big Spring

Council Ring Springs

Duck Pond Spring

Golf Course Spring

Woodrow Street Spring

Figure 1The Lake Wingra’s watershed encompasses primarily devolved land, meaning most of the inflow comes from storm water runoff. The lake is also fed by a number of springs.

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Figure 2Weirs measure the flow through a channel by forcing all of the water through a

notch at the top. We constructed this temporary weir at the Nakoma golf course.

Figure 3The flow can be calculated from a 120° weir with the formula Flow = 2.50 H5/2.

H is the height of the water in v-notch.

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H

120°

Figure 4A pygmy meter is attached to a wading rod and lowered into the stream. Each time the

spinner turns, the earphones omit a clicking sound. By counting the number of clicks in a minute we determined the velocity of the water at that point. Here the pygmy meter is

being used at the Arboretum big spring.

Figure 5This diagram illustrates how the cross section of a stream bed is divided into rectangles.

The flow in each rectangle is found by multiplying the area of the rectangle by the velocity of the water in the center of the rectangle. Summing the flows of all rectangles

yields the flow of the stream.

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