Cooperator: City
of Delafield, Lake Welfare Committee
Project Chief: Herbert S. Garn
Location: Waukesha County
Project Number: 9KB35
Period of Project: October 2002–September
2007
updated 10/18/07
Problem
The trophic state of Nagawicka Lake is mesotrophic-borderline eutrophic,
and quantified information on actual phosphorus loading sources and rates are
not available to accurately evaluate the potential changes in lake condition
under increased or decreased loading. Critical information to the City of Delafield,
Lake Welfare Committee necessary for the management of Nagawicka Lake is needed
to address identified nonpoint-pollution sources and stormwater management. Potential
changes in the water quality of Nagawicka Lake due to human activities and development
in the watershed, and operation of lake outlet structures to maintain water levels
and reduce flooding were identified as issues in the lake-management plan. The
effects of increasing development in the watershed and possible resulting increased
stormwater runoff and nutrient loading are a concern to residents, the City,
and other entities. In order to establish realistic water-quality goals for Nagawicka
Lake, accurate nutrient loading estimates are needed to enable water-quality
models to be calibrated and used to simulate future response of the lake. With
a calibrated model, the lake’s response to incremental increases or decreases
in phosphorus loading can be evaluated and used to refine the lake-management
plan.
Objective
This study will quantify the actual phosphorus and sediment loads entering and
leaving Nagawicka Lake from the Bark River watershed, and will determine how
incoming loads affect lake water quality.
The objectives of the proposed project are to:
• quantify the flows, phosphorus and sediment loads entering and leaving Nagawicka Lake;
• determine measured water and phosphorus budgets for Nagawicka Lake,
thereby providing a better understanding of the problems and sources of nutrients
for developing future lake management actions;
• relate the measured water and contaminant loads to observed and
modeled water-quality responses within the Lake; and
• model the response of the Lake to future phosphorus- loading scenarios
and to specific management actions aimed at reducing phosphorus loads to Nagawicka
Lake.
A better understanding of the hydrologic and phosphorus inputs
and potential response of the lake to various management scenarios will enhance
the management of Nagawicka Lake.
Approach
The study will consist of gage installation and two years of data collection
followed by data analysis and report preparation. Water quality will be sampled
six times per year in Nagawicka Lake and water levels will be recorded continuously
at a lake gage. To estimate the nutrient loading at the Bark River inlet and
outlet, daily streamflow will be measured and samples will be collected by automatic
water sampler at the inlet and manually at the outlet. To estimate nutrient loading
from other direct tributaries, three miscellaneous sites will also be sampled
manually and with siphon samplers. Phosphorus load data at the stream sites will
be used to estimate unit-area loads for unmonitored portions of the basin. These
measured data, along with other estimates, will be used to develop complete hydrologic
and phosphorus budgets for the lake. Concurrent water and phosphorus budgets
for the lake and in-lake water-quality data will be used to calibrate WiLMS (Wisconsin
Lake Modeling Suite) and used to estimate the response of the lake to various
phosphorus-loading scenarios.
Progress (October 2005 to September 2006)
Lake study complete.
Report received from printer, delivered to cooperator, and distributed. Lake
District continued operation of the Bark River inlet gage (discharge only) for
WY2007. The Upper Nemahbin Lake District discontinued funding discharge data
collection at the Nagawicka Lake outlet gage, Sept. 30, 2006.
Plans (October 2006 to September 2007)
Publish Bark River discharge
and load data in the WY2006 Annual Data Report. Continue ongoing streamflow data
collection at Bark River at Nagawicka Road stream-gaging station.
Report
Garn, H. S., Robertson, D. M., Rose, W. J., Goddard, G. L., and Horwatich, J.
A., 2006, Water quality, hydrology, and response to changes in phosphorus loading
of Nagawicka Lake, a calcareous lake in Waukesha County, Wisconsin: U.S. Geological
Survey Scientific Investigations Report 2006-5273, 41 p.
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