HomeMy WebLinkAboutLakeNancyOttoReport_072822Draft
D R A F T
Technical Evaluation of Phosphorus Loading Sources
and Reduction Approaches for Lake Nancy and Lake
Otto
Prepared for
Nine Mile Creek Watershed District
July 2022
i
Technical Evaluation of Phosphorus Loading Sources and Reduction
Approaches for Lake Nancy and Lake Otto
DRAFT July 2022
Contents
1 Introduction ........................................................................................................................................................................... 1
2 Background and Water Quality Monitoring Data ................................................................................................... 2
2.1 Lake Water Quality ............................................................................................................................................. 2
2.2 Phosphorus in Lake Bottom Sediments ..................................................................................................... 3
3 Water Quality Modeling and Lake Function ............................................................................................................. 7
4 Load Reduction Opportunities ....................................................................................................................................... 9
4.1 Lake Nancy Internal Loading Management ............................................................................................. 9
4.2 Fish Management .............................................................................................................................................10
4.2.1 Goldfish Removal .............................................................................................................................10
4.2.2 Winter Aeration to Minimize Recurrent Winterkill ..............................................................10
4.2.3 Stock Native Fish ..............................................................................................................................11
5 Conclusions and Project Cost Estimates ...................................................................................................................12
6 References ............................................................................................................................................................................13
ii
List of Tables
Table 1 Phosphorus mass balance (as kg total phosphorus) for Lake Nancy and Lake Otto for the June to September period. ...................................................................................................................... 8
Table 2 Predicted average change in phosphorus and chlorophyll a in Lake Nancy from June through September with internal load control during a dry (2021) and average (2017) year. .......................................................................................................................................................................... 9
Table 3 Suggested iron and aluminum dosing for Lake Nancy. ................................................................... 10
List of Figures
Figure 1 Surface water quality measurements for (a) total phosphorus; (b) chlorophyll a; (c) Secchi disk depth, and (d) a comparison of chlorophyll a and total Kjeldahl nitrogen (TKN) for Lake Nancy and Otto. .................................................................................................................... 4
Figure 2 Continuously measured dissolved oxygen in (a) Lake Nancy, and (b) Lake Otto. .................... 5
Figure 3 Concentration of Fe-P (a) and Org-P (b) in lake bottom sediment of Lake Nancy and Lake Otto. ............................................................................................................................................................... 6
Figure 4 Lake model calibration results for Lake Nancy (a,b) and Lake Otto (c,d) ..................................... 8
List of Attachments
Figure of Watersheds
1
1 Introduction
As part of ongoing water quality improvement efforts for Lake Cornelia and downstream waterbodies,
Barr Engineering Co. (Barr) conducted a monitoring and modeling investigation for Lake Nancy and Lake
Otto on behalf of the Nine Mile Creek Watershed District (NMCWD). Lake Nancy and Lake Otto are both
tributary to Lake Cornelia, and therefore water quality in these waterbodies can impact the water quality
in downstream Lake Cornelia. The objectives of the study were to evaluate the water quality of Lake Nancy
and Lake Otto, with a focus on understanding the potential for internal phosphorus loading in these
waterbodies and assessing potential opportunities to reduce phosphorus concentrations and improve
water quality. Because Lake Nancy and Lake Otto are tributary to Lake Cornelia, phosphorus reductions in
Nancy and Otto logically will reduce phosphorus concentrations in Lake Cornelia (note that much of the
water discharging from Lake Otto will be ultimately treated by the Rosland filtration system).
Fish surveys conducted in recent years by NMCWD indicate an abundant population of goldfish in Lake
Cornelia and Lake Nancy, which likely contributes to poor water quality conditions in both lakes. A
NMCWD study to track the movement of goldfish between Lake Cornelia and the upstream water bodies
is currently ongoing. Preliminary results indicate goldfish are not moving between Lake Cornelia and Lake
Nancy in significant numbers. However, data indicate that a large population of goldfish in Lake Nancy
approach the outlet structure and could move downstream to Lake Cornelia under the right conditions
(WSB, 2022). The NMCWD goldfish tracking study is anticipated to be completed in late-2022.
The watersheds tributary to Lake Nancy (111 acres) and Lake Otto (25 acres) are relatively small but
comprise 16 percent of the total watershed area tributary to North Lake Cornelia. Both tributary
watersheds consist of residential developments with minimal available open space and hence
opportunities to reduce pollutants from watershed runoff are limited. This study was focused on
identifying the potential benefit of applying in-lake methods for water quality improvement. Other
opportunities for reducing nutrient loading from the watershed, such as enhanced street sweeping, are
being explored by the NMCWD.
2
2 Background and Water Quality Monitoring Data
External phosphorus loading to Lake Cornelia estimated as part of the Lake Cornelia and Lake Edina Water
Quality Study (Barr Engineering, 2019), ranged from 93.7 kg (2017) to 137.4 kg (2016) from the June to
September period. While most of this load did not originate from the Lake Nancy or Lake Otto watershed,
the potential phosphorus contributions from these waterbodies resulting from internal loading has not
been previously evaluated. The turbid and green color of Lake Nancy and Lake Otto (but to lesser degree
in Lake Otto) noted in a review of historic aerial photographs, combined with concerns expressed by
residents of Lake Nancy and Lake Otto regarding poor water quality, prompted the Nine Mile Creek
Watershed District (NMCWD) to conduct this study. The primary objectives of the study are to evaluate
the water quality of Lake Nancy and Lake Otto, with a focus on understanding the potential for internal
phosphorus loading and opportunities to improve water quality in these lakes and downstream Lake
Cornelia.
The NMCWD conducted intensive monitoring in 2021 to better understand the water quality of Lake
Nancy and Lake Otto, the potential for internal phosphorus loading from lake bottom sediments, and how
it may influence the water quality of Lake Cornelia. The lake water quality monitoring and sediment
analyses are described in further detail below. Stormwater and lake water quality modeling were also
included as part this study to better understand the sources of phosphorus, the determinants of observed
water quality, and potential strategies to improve the water quality (see Section 3).
2.1 Lake Water Quality
The NMCWD conducted water quality monitoring of Lake Nancy and Lake Otto in 2021. The monitoring
consisted of 5 sampling events between May and September. Samples from each event were analyzed for
the following parameters: chlorophyll a, ammonia, nitrate + nitrite, total Kjeldahl nitrogen, total
phosphorus, total dissolved phosphorus, and orthophosphate. Samples were taken in the middle of Lake
Nancy and in the north-west and south-east basins of Lake Otto.
The monitoring results are summarized in Figure 1 for surface samples and select parameters. Review of
these graphs provides an initial understanding of how Lake Nancy and Lake Otto are functioning.
Figure 1a shows the changes in total phosphorus concentrations throughout the 2021 monitoring period.
The observed changes in total phosphorus concentrations in Lake Nancy, with phosphorus starting at the
lowest concentrations in the spring, increasing to a peak in mid-summer, and dropping in the fall, mimic a
classic signature of internal phosphorus loading from lake bottom sediments. Conversely, phosphorous in
Lake Otto does not mimic this pattern suggesting that external sources (e.g., stormwater runoff) is the
primary source of phosphorus to this lake. Changes in phytoplankton concentration (measured as
chlorophyll a) followed changes in total phosphorus in both lakes (Figure 1b). Water clarity, measured as
Secchi disk depth, is low for both lakes (Figure 1c). It is notable that total Kjeldahl nitrogen (TKN, organic
nitrogen plus ammonia) changed in concert with chlorophyll a for Lake Nancy and Lake Otto (Figure 1d).
Since there was very little runoff during the summer period, this suggests that phytoplankton are making
nitrogen (heterocyst cells in cyanobacteria / blue-green algae, make nitrogen). This suggests that if
phosphorus is reduced, this will also reduce nitrogen when blue-green algae growth is reduced.
3
Dissolved oxygen probes were placed mid-depth in Lake Otto and Lake Nancy to understand how
dissolved oxygen may be driving internal phosphorus loading from lake bottom sediments. The dissolved
oxygen measurements for Lake Nancy and Lake Otto are shown in Figure 2a and 2b, respectively. In Lake
Nancy, dissolved oxygen did not drop below 5 mg/L until July when the lake level dropped, and it is
possible that the probe dropped into the lake bottom sediments as the lake level lowered (the probe was
attached to a buoy at a fixed distance below the buoy). This does not change our understanding of the
dissolved oxygen dynamics in Lake Nancy as oxygen is low enough in the sediments to cause internal
loading. We often consider 2 mg/L and below as the dissolved oxygen threshold where phosphorus is
released from lake bottom sediments that are composed of iron-phosphate (Fe-P). The lake bottom
sediment data, described below (Section 2.2), suggest that internal loading is not coming from Fe-P but
rather organically-bound phosphorus (Org-P). Modeling results (Section 3) provide an indication of
internal loading magnitude. The measured dissolved oxygen data informed the management approach
for Lake Nancy and Lake Otto (see Section 4).
2.2 Phosphorus in Lake Bottom Sediments
In spring 2021, two sediment cores were collected and sectioned in Lake Nancy and two cores were
collected and sectioned in Lake Otto. Each core was analyzed for a range of phosphorus types (called
fractions), iron, percent water, and percent carbon. Results for Fe-P and Org-P are shown in Figure 3. Fe-P
in sediment in Lake Otto was below concentrations where internal loading can be expected (Pilgrim et. al.,
2007) whereas in Lake Nancy minimal internal loading can be expected from Fe-P. Org-P, however, is on
average 11 times greater than Fe-P, suggesting that internal loading in these lakes is primarily the result
of Org-P decay.
4
0
1
2
3
4
5
6
7
0 50 100 150 200TKN (mg/L)Chlorophyll a (µg/L)
d)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
5/4/21 6/23/21 8/12/21 10/1/21Total Phosphorus (mg/L)Nancy Otto North West
Otto South East
a
0
20
40
60
80
100
120
140
160
180
5/4/21 6/23/21 8/12/21 10/1/21Chlorophyll a(µg/L)Nancy Otto South East
b)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
5/4/21 6/23/21 8/12/21 10/1/21Secchi disk (m)Nancy Otto South East
c)
Figure 1 Surface water quality measurements for (a) total phosphorus; (b) chlorophyll a; (c) Secchi disk depth, and (d) a comparison of chlorophyll a and total Kjeldahl nitrogen (TKN) for Lake Nancy and Otto.
5
Figure 2 Continuously measured dissolved oxygen in (a) Lake Nancy, and (b) Lake Otto.
0
5
10
15
20
25
30
35
4/24/21 5/14/21 6/3/21 6/23/21 7/13/21 8/2/21Dissolved Oxygen (mg/L)a) Lake Nancy
0
5
10
15
20
25
4/24/21 5/14/21 6/3/21 6/23/21 7/13/21 8/2/21Dissolved Oxygen (mg/L)b) Lake Otto
6
Figure 3 Concentration of Fe-P (a) and Org-P (b) in lake bottom sediment of Lake Nancy and
Lake Otto.
0
2
4
6
8
10
12
14
16
18
0.000 0.002 0.004 0.006 0.008 0.010 0.012
Depth (cm)Sediment Fe-P (mg P/cm3 wet sediment)
Otto 1 Otto 2 Nancy 1 Nancy 2
a)
0
2
4
6
8
10
12
14
16
18
0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07
Depth (cm)Sediment Org-P (mg P/cm3 wet sediment)
Otto 1 Otto 2 Nancy 1 Nancy 2
b)
7
3 Water Quality Modeling and Lake Function
Water quality models are used to understand lake function, but they are also used to (1) connect field
measurements to nutrient loading estimates, (2) identify load reduction opportunities, and (3) estimate
expected lake response to proposed nutrient load reductions. Estimates of runoff volumes as well as
phosphorus and nitrogen loads from tributary watersheds were generated with the P8 model used for the
2019 Lake Cornelia and Lake Edina Water Quality Study (watersheds are identified in Figure 4). The Barr
Shallow Lake Model was used to: (1) estimate internal phosphorus loading, (2) determine the effect of
external loads on phosphorus concentrations in Lake Nancy and Lake Otto, (3) quantify the effect of
phosphorus concentrations on algal growth (measured as chlorophyll a), and (4) identify the benefit of
load reduction on phosphorus and chlorophyll a concentrations. Modeling was conducted for summer
2021 and 2017. Two years were modeled to understand lake function (e.g., external and internal loads,
and phytoplankton growth) during a dry year (2021) and an average year (2017). The model-generated
phosphorus mass balances are summarized in Table 1. Note that monitoring data for 2017 was not
available.
For Lake Nancy, lake model results indicate that internal loading was a significant source of phosphorus in
2017 and 2021 (see Table 1). In 2021, contributions of phosphorus from stormwater and internal loading
were similar, with internal loading being about 54 percent of the total load. In 2017, a more typical
precipitation year, internal phosphorus loading represented approximately 17 percent of total phosphorus
loading in Lake Nancy. As part of the model calibration process (see Figure 4) and the knowledge gained
as part of that process, it can be concluded that phosphorus is the primary driver of phytoplankton
(measured as chlorophyll a) growth. The primary source of phosphorus during the summer months is
internal loading and this also corresponds with the timing of phytoplankton blooms in the lake. It’s also
notable that Lake Nancy is only retaining between 15 to 26 percent of total phosphorus inputs during the
modeling period (mid-May through September) and it is not providing treatment needed to protect Lake
Cornelia during the critical summer months. The contribution of phosphorus to Lake Cornelia from Lake
Nancy during summer months is largely due to internal loading.
For Lake Otto, model results indicate there was minimal or no internal loading in 2017 and 2021. In 2021
during the modeling period, Lake Otto removed 100 percent of phosphorus inputs and in 2017 it was 98
percent (phosphorus is removed by settling). High removal was a function of the shallow lake depth (e.g.,
the distance for the sediment to settle is short) and hence rapid settling and minimal outflows. Note that
in 2021 the total mass of phosphorus in the lake at the start of modeling was more than the total mass at
the end of the modeling period, hence the mass balance makes it appear that more than 100 percent of
the phosphorus entering Lake Otto was removed. Similar to Lake Nancy, it can be concluded from the
lake model calibration process that phytoplankton (measured as chlorophyll a) growth in Lake Otto is a
function of phosphorus concentration in the lake; in this case the primary source of phosphorus is from
stormwater runoff.
8
0
0.1
0.2
0.3
0.4
0.5
4/14/21 6/3/21 7/23/21 9/11/21 10/31/21Total Phosphorus (mg/L)Total Phosphorus Calibration:
Lake Nancy
Modeled
a)
0
50
100
150
200
250
4/14/21 6/3/21 7/23/21 9/11/21 10/31/21Chlorophyll a(ug/L)Chlorophyll a Calibration:
Lake Nancy
Modeled
Monitored
b)
0
0.02
0.04
0.06
0.08
0.1
0.12
4/14/21 6/3/21 7/23/21 9/11/21 10/31/21Total Phosphorus (mg/L)Total Phosphorus Calibration:
Lake Otto
Modeled
Monitored
c)
0
10
20
30
40
50
4/14/21 6/3/21 7/23/21 9/11/21 10/31/21Chlorophyll a(ug/L)Chlorophyll a Calibration: Lake Otto d)
Table 1 Phosphorus mass balance (as kg total phosphorus) for Lake Nancy and Lake Otto for the June to September period.
Lake Year
In
Out
Total
Settled
Settled in
Phytoplankton
Difference In-
Lake Mass Stormwater
Internal
Load
Lake Nancy 2021 1.7 2.0 2.1 1.0 0.2 -0.7
Lake Nancy 2017 10 2.0 8.8 1.7 0.2 -1.5
Lake Otto 2021 3.0 0.0 0.0 3.2 0.3 0.2
Lake Otto 2017 3.6 0.0 0.1 3.5 0.0 0.0
Figure 4 Lake model calibration results for Lake Nancy (a,b) and Lake Otto (c,d)
Although the lake modeling results suggest that there was likely very little internal loading in Lake Otto in
2021, there was a gradual increase in phosphorus from June through September and this pattern of
increase is often indicative of internal loading. However, from June through early August water level was
declining because of evaporation, potentially concentrating phosphorus in the Lake Otto water column. It
is noteworthy that internal loading can vary year to year based on varying climatic conditions.
9
4 Load Reduction Opportunities
Based on results of the monitoring and modeling analyses, in-lake phosphorus load reduction
opportunities evaluated as part of this study are summarized below. The in-lake management activities
recommended for consideration are focused on Lake Nancy. Study results indicate the water quality of
Lake Otto is relatively good, with minimal internal phosphorus loading in 2017 and 2021 and a significant
percentage of stormwater loads being captured by settling to the lake bottom sediments. Additionally,
much of the water that passes downstream from Lake Otto will be treated by the Rosland Park stormwater
filtration system. From the perspective of improving water quality in Lake Cornelia, no additional action is
recommended at this time for Lake Otto.
Since the Lake Otto and Lake Nancy watersheds are mostly fully developed, with little or no public land
available to implement BMPs, the opportunities for reductions in external nutrient loading from these
watersheds are limited. Enhanced street sweeping, tentatively under consideration by the City of Edina
and NMCWD, would likely benefit Lake Otto and Lake Nancy. The NMCWD implements a cost share
program to promote stewardship and encourage water quality improvement practices such as rainwater
gardens and shoreline buffers on public and private lands. The NMCWD is also developing a fertilizer
optimization program to promote soil testing and proper application of nutrients to residential lawns.
4.1 Lake Nancy Internal Loading Management
For Lake Nancy, model results indicate that internal loading was a significant source of phosphorus in
2017 and 2021. Through analysis of the sediment, Fe-P was low and below concentrations where internal
loading is expected, but Org-P was notably higher, suggesting that internal loading in Lake Nancy is the
result of Org-P decay. Given this conclusion, conducting an alum treatment alone may not effectively
prevent internal loading in Lake Nancy, as alum treatment targets Fe-P in lake bottom sediments. Instead,
we are recommending an aluminum treatment be conducted in conjunction with the addition of iron to
capture Org-P when it decays (and form Fe-P) and installation of an aeration system to keep Fe-P in the
sediment. Table 2 summarizes the estimated change in phosphorus and chlorophyll a levels in Lake Nancy
resulting from internal phosphorus load control. Table 3 summarizes the suggested dosing rates for
aluminum and iron in Lake Nancy.
Table 2 Predicted average change in phosphorus and chlorophyll a in Lake Nancy from June through September with internal load control during a dry (2021) and average (2017)
year.
Total Phosphorus (mg/L) Chlorophyll a (µg/L)
Lake Year
No
Treatment
Internal Load
Treatment No Treatment
Internal Load
Treatment
Lake Nancy 2021 0.270 0.141 143 51
Lake Nancy 2017 0.262 0.213 113 43
10
Table 3 Suggested iron and aluminum dosing for Lake Nancy.
Treatment Area (ac)
Dosing Aluminum (Sodium Aluminate) Iron
Al (g m-2) Fe (g m-2) Gallons per Acre Total Gallons Gallons per Acre Total Gallons
4.2 16 70 116 490 131 554
4.2 Fish Management
A fish survey was conducted by NMCWD in Lake Nancy, Lake Cornelia (North and South), Point of France
Pond, and Swimming Pool Pond in 2019. A fish survey was not conducted in Lake Otto primarily due to
access constraints related to the specific equipment used at the time. The NMCWD intends to conduct a
fish survey in Lake Otto in 2023, if feasible.
The 2019 fish survey and follow-up studies in recent years indicate an abundant population of goldfish in
Lake Nancy and downstream Lake Cornelia, likely contributing to poor water quality conditions in both
lakes. Preliminary results from a NMCWD study to track the movement of goldfish between Lake Cornelia
and the upstream water bodies indicate goldfish are not moving between Lake Cornelia and Lake Nancy
in significant numbers but have the potential to move downstream to Lake Cornelia under the right
conditions (WSB, 2022). Additional information regarding the movement of goldfish between Lake Nancy
and Lake Cornelia will be available upon completion of the study, anticipated in late-2022. However, as
identified in the Lake Cornelia and Lake Edina Water Quality Improvement Project Feasibility
Study/Preliminary Engineering Report prepared by Barr in 2020, an integrated approach to goldfish
management using a combination of management actions is anticipated to be the most successful option.
Several fish management activities considered for Lake Nancy are briefly summarized below.
4.2.1 Goldfish Removal
There are several potential methods to remove goldfish, including biological control, lake drawdown,
physical removal, and chemical control. A combination of physical removal and biological control
(predation) would be the preferred approach (versus lake drawdown and/or chemical treatment), as
removal efforts can be selective/targeted to goldfish to reduce impacts to other fish and wildlife.
Additional information obtained from the ongoing goldfish tracking study should help assess the
potential effectiveness of a targeted removal effort in Lake Nancy.
4.2.2 Winter Aeration to Minimize Recurrent Winterkill
Winter fish kills, common in shallow lakes, can eliminate predator fish and lead to more successful survival
of undesirable fish such as goldfish and carp. Winter aeration is a management technique used to prevent
periodic winter fish kill and promote the establishment of a self-sustaining native fish population, which
would reduce the goldfish population in Lake Nancy. As previously mentioned in Section 4.1, aeration is
being recommended during the summer months in conjunction with alum treatment and additional iron
to the sediments to keep Fe-P in the lake sediments. If an aeration system is installed for internal loading
11
control, it could also be operated throughout the winter to help maintain a self-sustaining native predator
fish population.
4.2.3 Stock Native Fish
Stocking of native fish such as bluegill or largemouth bass should be considered to reduce success of
goldfish recruitment following initial removal of a large biomass of the existing goldfish population and
mitigation of winterkill with aeration. This will allow for the development of a self-sustaining native fish
population that can compete with goldfish.
12
5 Conclusions
Water quality in Lake Nancy and Lake Otto, small waterbodies tributary to Lake Cornelia, can impact the
water quality in downstream Lake Cornelia. The objectives of this investigation were to evaluate the water
quality of Lake Nancy and Lake Otto, with a focus on understanding the potential for internal phosphorus
loading in these waterbodies and assessing potential opportunities to reduce phosphorus concentrations
and improve water quality.
Monitoring and modeling results indicate that water quality in Lake Nancy is poor, with internal loading
being a significant source of phosphorus in Lake Nancy in 2017 and 2021. Through analysis of the
sediment, concentrations of iron-phosphate (Fe-P) were low and below concentrations where internal
loading is expected, but organically-bound phosphorus (Org-P) concentrations were notably higher,
suggesting that internal loading in Lake Nancy is the result of Org-P decay.
Study results indicate the water quality of Lake Otto is relatively good, with minimal internal phosphorus
loading identified in 2017 and 2021. The in-lake modeling analysis indicated a significant percentage of
phosphorus from stormwater runoff is being captured and settled to the lake bottom. Additionally, much
of the water that passes downstream from Lake Otto will be treated by the Rosland Park stormwater
filtration system. From the perspective of improving water quality in Lake Cornelia, no additional action is
recommended at this time for Lake Otto.
The following management actions have been identified for consideration to reduce the internal loading
in Lake Nancy and improve the water quality of Lake Nancy and downstream Lake Cornelia:
(1) Alum / Iron Treatment / Aeration: Aluminum (as sodium aluminate) and iron (as ferric chloride)
application are recommended to prevent internal phosphorus loading from Lake Nancy bottom
sediments. For iron to be effective, aeration is necessary to keep the lake bottom sediments
oxygenated. This system is envisioned to be a simple bubbler type aerator where a compressor is
installed near the shore with aerator lines extending into the lake. Operation could be just
summer but winter operation would also have benefits with respect to maintaining a self-
sustaining fish population over the winter. This would benefit goldfish control efforts.
(2) Consideration of Additional Fish Management Efforts: Fish surveys conducted in recent years
by NMCWD indicate an abundant population of goldfish in Lake Nancy, likely contributing to
poor water quality conditions in the lake. While still to be confirmed, preliminary results from a
NMCWD study tracking the movement of goldfish between Lake Cornelia and the upstream water
bodies indicate goldfish are not moving between Lake Cornelia and Lake Nancy in significant
numbers but have the potential to move downstream to Lake Cornelia under the right conditions.
Upon receipt of final results of the goldfish tracking study, an integrated approach to goldfish
management in Lake Nancy should be considered, including goldfish removal (preferably using
selective methods targeted to goldfish), winter aeration to minimize recurrent winterkill of
predator species, and stocking of native fish.
13
6 References
Barr Engineering Co. 2019. Lake Cornelia and Lake Edina Water Quality Study, Use Attainability Analyses
for Lake Cornelia (updated from 2010) and Lake Edina (first version). Nine Mile Creek Watershed District.
July 2019.
Barr Engineering Co.. 2020. Lake Cornelia and Lake Edina Water Quality Improvement Project Feasibility
Study/Preliminary Engineering Report. Nine Mile Creek Watershed District. June 2020.
Pilgrim et. al., 2007. A Method for Comparative Evaluation of Whole-lake and Inflow Alum Treatment.
Water Research. 41(6):1215-24.
WSB. 2022. Goldfish Population and Management: Feasibility Study in the Lake Cornelia System (DRAFT).
Nine Mile Creek Watershed District. January 2022.
Attachment
Figure of Watershed
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North LakeCornelia
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Barr Footer: ArcGIS 10.8.1, 2022-03-11 13:17 File: I:\Client\Nine_Mile_Creek_WD\Work_Orders\23270634_Project\2018_Cornelia_Edina_UAA\Maps\Basemaps\Figure4_P8_Watersheds.mxd User: vawLake Nancy and LakeOtto WatershedsNMCWD
FIGURE 5
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District LegalBoundary (2017)
Imagery Source: Nearmap 09/09/2021