Spring flow and water quality in the Lake Wingra watershed

Spring flow and water quality in the Lake Wingra watershed Nick Ballering, Professor Jean Bahr Department 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 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 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 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 the golf course This weir is shown in Figure 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 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 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 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 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 The duck pond flowed at ft^3/s and the Arboretum spring flowed at approximately ft^3/s It ranged up and down by 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 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 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 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 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 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 The Institute for Environmental Studies, The Water Resources Management Workshop, and the University of Wisconsin Madison; Lake Wingra Watershed: A New Management Approach; 1999 Stevens; Water Resources Data Book,4th Edition; Leupold & Stevens, Inc.; 1987 Herschy, Reginald W; Streamflow Measurement: Second Edition; Elsevier Applied Science Publishers Ltd.; 1995 Woodrow Street Spring Council Ring Springs Duck Pond Spring Arboretum Big Spring Golf Course Spring Figure The 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 Figure Weirs 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 H 120° Figure The 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 10 Figure A 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 This 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 11 ...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... 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... 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