HomeMy WebLinkAboutSECTION_11 U.S. HIGHWAY `169 NORTH
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11.0 T.H. 169 North
11.1 General Description of Drainage Area
Figure 11.1 depicts the T.H. 169 North drainage area and the individual subwatersheds within this
area. The T.H. 169 North drainage area is located in the northwest corner of Edina. The drainage
area encompasses approximately 140 acres that ultimately drain to the T.H. 169 drainage system.
11.1.1 Drainage Patterns
The stormwater system within this drainage area is comprised of storm sewers, ditches, overland
flow paths, and ponding basins. Stormwater from this drainage area ultimately combines with the
T.H. 169 storm sewer system at several locations along T.H. 169 between the intersection of Malibu
Drive and T.H. 169 and the Edina city limits. The drainage area has been delineated into
23 subwatersheds. Table 11.1 describes the naming convention for subwatersheds within the
drainage area. Land use within the drainage area includes low-density residential, open area, Van
Valkenburg Park, and a small commercial area.
Table 11.1 Major Watershed within the T.H. 169 North Drainage Area
Major Watershed
Subwatershed Naming
Convention
# of
Subwatersheds
Drainage
Area (acres)
T.H. 169 North 169N_## 23 140
11.2 Stormwater System Analysis and Results
11.2.1 Hydrologic/Hydraulic Modeling Results
The 10-year and 100-year frequency flood analyses were performed for the T.H. 169 North drainage
area. The 10-year analysis was based on a ½-hour storm of 1.65 inches of rain. The 100-year
analysis was based on a 24-hour storm event of 6 inches of rain. Table 11.2 presents the watershed
information and the results for the 10-year and 100-year frequency hydrologic analyses for the
T.H. 169 North drainage area.
The results of the 10-year and 100-year frequency hydraulic analysis for the T.H. 169 North drainage
area are summarized in Table 11.3 and Table 11.4. The column headings in Table 11.3 are defined
as follows:
Node/Subwatershed ID—XP-SWMM node identification label. Each XP-SWMM node
represents a manhole, catchbasin, pond, or other junction within the stormwater system.
Downstream Conduit—References the pipe downstream of the node in the storm sewer system.
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Flood Elevation—The maximum water elevation reached in the given pond/manhole for each
referenced storm event (mean sea level). In some cases, an additional flood elevation has been
given in parenthesis. This flood elevation reflects the 100-year flood elevation of Nine Mile
Creek, per the Nine Mile Creek Watershed Management Plan, May 1996.
Peak Outflow Rate—The peak discharge rate (cfs) from a given ponding basin for each
referenced storm event. The peak outflow rates reflect the combined discharge from the pond
through the outlet structure and any overflow.
NWL—The normal water level in the ponding basin (mean sea level). The normal water levels
for the ponding basins were assumed to be at the outlet pipe invert or at the downstream control
elevation.
Flood Bounce—The fluctuation of the water level within a given pond for each referenced storm
event.
Volume Stored—The maximum volume (acre-ft) of water that was stored in the ponding basin
during the storm event. The volume represents the live storage volume only.
Table 11.4 summarizes the conveyance system data used in the model and the model results for the
storm sewer system within the T.H. 169 North drainage area. The peak flows through each
conveyance system for the 10-year and 100-year frequency storm events are listed in the table. The
values presented represent the peak flow rate through each pipe system only and does not reflect the
combined total flow from an upstream node to the downstream node when overflow from a
manhole/pond occurs.
Figure 11.2 graphically represents the results of the 10-year and 100-year frequency hydraulic
analyses. The figure depicts the T.H. 169 North drainage area boundary, subwatershed boundaries,
the modeled storm sewer network, and surcharge conditions for the XP-SWMM nodes (typically
manholes).
One of the objectives of the hydraulic analyses was to evaluate the level of service provided by the
current storm sewer system. The level of service of the system was examined by determining the
surcharge conditions of the manholes and catch basins within the storm sewer system during the
10-year and 100-year frequency storm events. An XP-SWMM node was considered surcharged if the
hydraulic grade line at that node breached the ground surface (rim elevation). Surcharging is
typically the result of limited downstream capacity and tailwater impacts. The XP-SWMM nodes
depicted on Figure 11.2 were color coded based on the resulting surcharge conditions. The green
nodes signify no surcharging occurred during the 100-year or 10-year frequency storm event, the
yellow nodes indicate surcharging during the 100-year frequency event, and the red nodes identify
that surcharging is likely to occur during both a 100-year and 10-year frequency storm event.
Figure 11.2 illustrates that several XP-SWMM nodes within the T.H. 169 North drainage area are
predicted to experience surcharged conditions during both the 10-year and 100-year frequency storm
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events. This indicates a probability greater than 10 percent in any year that the system will be
overburdened and unable to meet the desired level of service at these locations. These manholes and
catch basins are more likely to experience inundation during the smaller, more frequent storm events
of various durations.
Another objective of the hydraulic analysis was to evaluate the level of protection offered by the
current stormwater system. Level of protection is defined as the capacity provided by a municipal
drainage system (in terms of pipe capacity and overland overflow capacity) to prevent property
damage and assure a reasonable degree of public safety following a rainstorm. A 100-year frequency
event is recommended as a standard for design of stormwater management basins. To evaluate the
level of protection of the stormwater system within the T.H. 169 North drainage area, the 100-year
frequency flood elevations for the ponding basins and depressed areas were compared to the low
elevations of structures surrounding each basin. Based on the analysis, the current system in the
T.H. 169 North drainage area is providing a 100-year level of protection. Therefore, no storm sewer
or pond upgrades are being recommended at this time.
11.2.2 Water Quality Modeling Results
The effectiveness of the stormwater system in removing stormwater pollutants such as phosphorus
was analyzed using the P8 water quality model. The P8 model simulates the hydrology and
phosphorus loads introduced from the watershed of each pond and the transport of phosphorus
throughout the stormwater system. Since site-specific data on pollutant wash-off rates and sediment
characteristics were not available, it was necessary to make assumptions based on national average
values. Due to such assumptions and lack of in-lake water quality data for model calibration, the
modeling results were analyzed based on the percent of phosphorus removal that occurred and not
based on actual phosphorus concentrations.
Figure 11.3 depicts the results of the water quality modeling for the T.H. 169 North drainage area.
The figure shows the fraction of total phosphorus removal for each water body as well as the
cumulative total phosphorus removal in the watershed. The individual water bodies are colored
various shades of blue, indicating the percent of the total annual mass of phosphorus entering the
water body that is removed (through settling). It is important to note that the percent of phosphorus
removal is based on total phosphorus, including phosphorus in the soluble form. Therefore, the
removal rates in downstream ponds will likely decrease due to the large soluble fraction of incoming
phosphorus that was unsettleable in upstream ponds. The watersheds are depicted in various shades
of gray, indicating the cumulative total phosphorus removal achieved. The cumulative percent
removal represents the percent of the total annual mass of phosphorus entering the watershed that is
removed in the pond and all upstream ponds.
Ponds that had an average annual total phosphorus removal rate of 60 percent or greater, under
average climatic conditions, were considered to be performing well. For those ponds with total
phosphorus removal below 60 percent, the permanent pool storage volume was analyzed to determine
if additional capacity is necessary. Based on recommendations from the MPCA publication
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Protecting Water Quality in Urban Areas, March 2000, the permanent pool for detention ponds
should be equal to or greater than the runoff from a 2.0-inch rainfall, in addition to the sediment
storage for at least 25 years of sediment accumulation. For ponds with less than 60 percent total
phosphorus removal, the recommended storage volume was calculated for each pond within the
drainage basin and compared to the existing permanent pool storage volume.
11.3 Implementation Considerations
The XP-SWMM hydrologic and hydraulic modeling analyses and P8 water quality analysis helped to
identify locations throughout the watershed where improvements to the City’s stormwater
management system may be warranted. The following sections discuss potential mitigation
alternatives that were identified as part of the 2003 modeling analyses. As opportunities to address
the identified flooding issues and water quality improvements arise, such as street reconstruction
projects or public facilities improvements, the City will use a comprehensive approach to stormwater
management. The comprehensive approach will include consideration of infiltration or volume
retention practices to address flooding and/or water quality improvements, reduction of impervious
surfaces, increased storm sewer capacity where necessary to alleviate flooding, construction and/or
expansion of water quality basins, and implementation of other stormwater BMPs to reduce pollutant
loading to downstream waterbodies.
11.3.1 Flood Protection Projects
The 2003 hydrologic and hydraulic modeling analysis identified several locations within the
T.H. 169 North drainage basin where the 100-year level of protection is not provided by the current
stormwater system. The problem areas identified in 2003 are discussed below.
As part of the 2003 modeling analysis, potential corrective measures were identified for the problem
areas for purposes of developing planning-level cost estimates. These preliminary corrective
measures are also discussed below. As the City evaluates the flooding issues and potential system
modifications in these areas, consideration will be given to other potential system modifications,
including implementation of stormwater infiltration or volume retention practices, where soils are
conducive.
11.3.2 Construction/Upgrade of Water Quality Basins
The 2003 P8 modeling analysis indicated that the predicted annual removal of total phosphorus from
Pond 169N_16 in the T.H. 169 North drainage area was below the desired 60 percent removal rate,
under average year conditions. The permanent pool storage volume was analyzed to determine if
additional capacity is necessary. The basin was found to have sufficient dead storage volume, based
on the MPCA recommended permanent pool storage volume for detention basins for the removal of
particulate phosphorus. As a result, no specific recommendations for water quality basin upgrades in
the T.H. 169 North drainage area are being made at this time.
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Construction of new or expansion of existing water quality basins is one method to increase the
pollutant removal achieved prior to stormwater reaching downstream waterbodies. Many additional
techniques are available to reduce pollutant loading, including impervious surface reduction or
disconnection, implementation of infiltration or volume retention BMPs, installation of underground
stormwater treatment structures and sump manholes and other good housekeeping practices such as
street sweeping. As opportunities arise, the City will consider all of these options to reduce the
volume and improve the quality of stormwater runoff.
Table 11.2
Watershed Modeling Results for Subwatersheds in the T.H. 169-North Drainage Area (Revised 12/2006).
Watershed ID
Total Area
(ac)
% Impervious
Area
Peak Runoff Rate
(cfs)
Total Volume
Runoff (ac-ft)
Peak Runoff Rate1
(cfs)
Total Volume
Runoff (ac-ft)
169N_1 5.5 21 23.5 1.58 12.5 0.33
169N_2 1.0 20 4.9 0.29 3.9 0.07
169N_3 2.0 20 9.0 0.56 5.1 0.12
169N_4 9.4 20 35.6 2.67 16.9 0.52
169N_5 1.7 20 7.9 0.47 5.9 0.11
169N_6 1.0 14 4.5 0.26 3.6 0.00
169N_7 3.6 24 15.7 1.13 9.2 0.25
169N_8 2.1 20 9.7 0.58 6.9 0.14
169N_9 8.5 12 29.3 2.15 11.1 0.36
169N_10 6.7 19 29.5 1.85 15.6 0.39
169N_11 8.5 20 33.6 2.35 16.1 0.45
169N_12 12.0 13 50.3 3.16 21.5 0.62
169N_13 12.4 9 46.4 3.07 16.1 0.53
169N_14 3.3 20 15.3 0.93 9.4 0.21
169N_15 8.2 0 33.2 1.87 10.9 0.32
169N_16 2.4 15 10.7 0.63 5.8 0.14
169N_17 19.5 2 66.1 4.36 19.0 0.70
169N_18 4.9 41 23.1 1.80 18.5 0.44
169N 19 4.2 3 18.5 0.99 7.7 0.19
Watershed Information 10-Year Storm Results
1/2-Hour Event24-Hour Event
100-Year Storm Results
169N_19 4.2 3 18.5 0.99 7.7 0.19
169N_20 9.0 16 35.8 2.42 15.9 0.46
169N_21 3.2 20 11.1 0.86 5.1 0.16
169N_22 5.3 63 25.4 2.16 24.4 0.55
169N_23 6.0 0 25.3 1.47 9.8 0.29
1 In some cases, the 10-year peak runoff rate is higher than the 100-year peak runoff rate as a result of the differences in peak intensity of the
rainfall hydrographs.
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Table 11.3
Flood
Elevation1 (ft)
Type of
Storage2 NWL (ft)
Flood Bounce
(ft)
Flood
Elevation (ft) NWL (ft)
Flood Bounce
(ft)
94 outlet to TH 169 system 914.5 912.5
106 outlet to TH 169 system 912.7 912.2
108 outlet to TH 169 system 909.3 908.8
1395 1102 939.9 938.0
1399 1104 939.3 byd 934.4 4.9 938.0 934.4 3.6
1400 1106 937.7 937.4
1401 1107 937.4 937.1
1402 1108 937.0 935.1
1404 1110 925.4 923.9
1406 1112 924.1 920.9
1408 1114 923.4 918.8
1409 1115 924.3 918.5
1411 outlet to TH 169 system 918.5 915.9
1413 1118 932.8 932.4
1416 1121 928.2 927.9
1427 1131 902.7 898.8
1428 1132 908.7 904.9
1429 1133 921.8 917.9
1431 95 915.1 913.6
1435 1137 924.2 913.0
1436 1138 905.3 901.3
1437 1139 901.6 897.4
Hydraulic Modeling Results for XP-SWMM Subwatersheds/Nodes in the T.H. 169-North Drainage Area (Revised 12/2006)
Subwatershed or
Node Downstream Conduit
100-Year Storm Results
24-Hour Event
10-Year Storm Results
1/2-Hour Event
1439 1141 893.9 891.0
1440 1142 893.8 890.3
1441 1143 905.0 902.1
1443 outlet to TH 169 system 877.3 876.4
2486 1322 913.7 910.8
2487 1323 913.7 910.7
169N_1 107 914.3 913.6
169N_2 1103 953.0 949.1
169N_3 1113 923.0 919.1
169N_4 1119 932.5 932.2
169N_5 2021 918.0 917.1
169N_6 1154 972.2 971.2
169N_7 120 918.0 914.4
169N_8 1101 943.7 942.5
169N_9 1111 922.4 921.8
169N_10 1109 925.9 924.9
169N_11 1116 921.5 917.5
169N_12 1130 935.2 932.6
169N_13 1134 916.0 915.7
169N_14 1105 939.2 938.9
169N_15 landlocked 932.5 depression 925.5 7.0 928.7 925.5 3.2
169N_16 1136 923.8 pond 914.4 9.4 918.9 914.4 4.5
169N_17 1135 926.7 922.4
169N_18 1144 899.5 898.9
169N_19 1140 910.2 907.1
169N_20 1117 935.0 934.8
169N_21 1120 930.6 930.2
169N_22 69 910.96 910.2
169N_23 1321 913.67 depression 910.9 2.8 911.7 910.9 0.8
1 100-year flood elevation based on 24-hour event. Flood elevation from a 10-day snowmelt event should also be evaluated prior to final design/determination.
11-7
1
Table 11.4
Conduit Modeling Results for Subwatersheds in the T.H. 169-North Drainage Area (Revised 12/2006)
Conduit ID Upstream Node Downstream Node Conduit Shape
Conduit
Dimensions (ft)
Roughness
Coefficient
Upstream Invert
Elevation
(ft)
Downstream Invert
Elevation
(ft)
Conduit Length
(ft)Slope
100Y Peak Flow
through Conduit
(cfs)
10Y Peak Flow
through Conduit
(cfs)
69 169N_22 108 Circular 2.0 0.013 904.16 903.93 31 0.7 38.4 34.2
95 1431 94 Circular 2.0 0.013 908.17 908.06 43 0.3 34.8 34.7
107 169N_1 106 Circular 1.0 0.013 909.31 909.27 19 0.2 6.9 6.1
120 169N_7 109 Circular 2.0 0.013 909.28 907.17 118 1.8 38.5 28.9
1101 169N_8 1395 Circular 1.25 0.013 941.86 936.25 123 4.6 9.7 6.9
1102 1395 1399 Circular 1.5 0.013 936.25 935.80 45 1.0 9.7 6.9
1103 169N_2 169N_14 Circular 1.0 0.024 944.57 934.04 280 3.8 4.5 3.8
1105 169N_14 1400 Circular 1.0 0.024 934.04 933.08 299 0.3 2.4 2.4
1106 1400 1401 Circular 1.0 0.013 933.08 932.50 161 0.4 2.4 2.3
1111 169N_9 1406 Circular 2.0 0.014 919.01 918.26 188 0.4 18.1 18.8
1112 1406_e 169N_3 Circular 2.0 0.013 918.26 916.56 335 0.5 17.0 17.0
1113 169N_3 1408 Circular 3.0 0.013 916.06 914.81 324.7 0.4 22.7 21.9
1114 1408 1409 Circular 3.0 0.013 914.80 913.28 331.1 0.5 29.3 24.1
1115 1409 169N_11 Circular 3.0 0.013 913.27 911.99 338.6 0.4 41.1 37.5
1116 169N_11 1411 Circular 3.0 0.013 912.05 910.51 290.2 0.5 62.9 49.3
1135 169N_17 169N_16 Circular 2.0 0.013 920.83 918.50 94 2.5 41.2 21.0
1136 169N_16 1435 Circular 1.0 0.013 919.50 917.10 65 3.7 6.8 0.0
1137 1435 1436 Circular 1.0 0.013 914.00 911.26 70 3.9 7.8 0.0
1138 1436 1437 Circular 1.0 0.013 911.26 906.11 220 2.3 7.5 0.0
1140 169N_19 1439 Circular 1.5 0.013 905.89 905.40 63 0.8 18.0 7.7
1141 1439 1440 Circular 1.75 0.013 905.40 899.92 218 2.5 23.2 7.7
1143 1441 169N_18 Circular 2.0 0.013 899.40 898.83 10 5.7 27.1 8.0
1154 169N_6 1462 Circular 1.0 0.013 970.20 969.34 59.8 1.4 4.5 3.6
1104 1399 169N_14 Circular 1.0 0.024 934.40 934.04 30 1.2 -4.1 -5.6
1107 1401 1402 Circular 1.0 0.013 932.23 931.91 66 0.5 6.6 6.3
1108 1402 169N_10 Circular 1.0 0.013 931.91 920.04 315 3.8 7.5 6.4
1109 169N_10 1404 Circular 1.75 0.013 920.04 919.58 60 0.8 26.1 20.5
1110 1404 169N_9 Circular 1.75 0.013 919.58 919.01 161 0.4 21.2 16.9
1117 169N_20 1413 Circular 1.5 0.013 928.60 926.10 331.3 0.8 10.9 10.4
1118 1413 169N_4 Circular 1.75 0.013 926.10 925.30 136.5 0.6 10.7 14.1
1119 169N_4 169N_21 Circular 1.75 0.013 925.30 924.20 197 0.6 23.9 24.4
1120 169N_21 1416 Circular 2.25 0.013 924.20 921.54 333 0.8 26.6 27.8
1121 1416 169N_5 Circular 1.5 0.013 921.54 911.00 270 3.9 22.2 22.6
1130 169N_12 1427 Circular 1.75 0.013 927.64 924.34 330 1.0 24.3 21.6
1131 1427 1428 Circular 1.75 0.013 924.34 918.40 151 3.9 27.2 21.2
1132 1428 1429 Circular 2.0 0.024 917.99 914.13 189 2.0 30.1 21.2
1133 1429 169N_13 Circular 2.0 0.013 914.13 908.72 266 2.0 32.1 19.5
1134 169N_13 1431 Circular 2.0 0.013 908.82 908.26 71 0.8 33.7 33.8
1139 1437 169N_19 Circular 1.0 0.013 906.11 905.89 27 0.8 7.0 -0.2
1142 1440 1441 Circular 1.75 0.024 899.67 898.95 10 7.2 16.8 8.0
1144 1442 169N_18 Circular 2.0 0.013 898.83 898.09 153 0.5 37.0 25.3
1321 169N_23 2486 Circular 2.0 0.013 910.87 908.70 6 36.2 21.8 9.9
1322 2486 2487 Circular 2.0 0.013 907.71 907.53 28 0.6 21.9 10.0
1323 2487 169N_22 Circular 2.0 0.013 907.51 904.29 68 4.7 31.0 14.2
2021 169N_5 1413 Circular 1.5 0.013 911.00 909.28 45.2 3.81 27.9 28.8
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169N_13
169N_12
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169N_9
169N_20
169N_11
169N_15
169N_10
169N_1
169N_23
169N_22
169N_18
169N_19
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169N_21
169N_8
169N_16
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Figure 11.1
T.H. 169 NORTH
DRAINAGE BASIN
Comprehensive Water Resource
Management Plan
City of Edina, Minnesota
200 0 200
Meters
City of Edina Boundary
Roads/Highways
Creek/Stream
Lake/Wetland
T.H. 169 North Drainage Basin
Subwatershed
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169N_17
169N_13
169N_12
169N_4
169N_9
169N_20
169N_11
169N_15
169N_10
169N_1
169N_23
169N_22
169N_18
169N_19
169N_7
169N_14
169N_21
169N_8
169N_16
169N_3
169N_5 169N_2
169N_6
94
119
108
106
1411
1443 1439
1436
1434
1433
1409 1408
1406
1396
1395
169N_6
169N_3
169N_8
169N_23
169N_11
2487
2486
1437
1435
1429 1428 1427
1416
1413
1404 1402
169N_1
169N_4
169N_2
169N_22
169N_19
169N_17
169N_12
169N_21
1441
1462
1440
1431
1401 1400
169N_7 169N_5
169N_9
169N_18
169N_13
169N_20
169N_10
169N_14
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400 0 400
Feet
Figure 11.2
T.H. 169 NORTH
HYDRAULIC MODEL RESULTS
Comprehensive Water Resource
Management Plan
City of Edina, Minnesota
150 0 150
Meters
City of Edina Boundary
Roads/Highways
Lake/Wetland
T.H. 169 North Drainage Basin
Subwatershed
Major Watershed
Pipes
!.Manhole
!.Manhole Surcharge During
100-Year Frequency Event
!.Manhole Surcharged During
10-Year Frequency Event
Imagery Source: Aerials Express, 2008
£¤169
11-10
HopkinsHopkins 169N_16
169N_15
!;N
Ba
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4000400
Feet
Figure 11.3
T.H. 169 NORTH
WATER QUALITY
MODELING RESULTS
Comprehensive Water Resource
Management Plan
City of Edina, Minnesota
150 0 150
Meters
Imagery Source: Aerials Express, 2008
25 - 40% (Moderate Removal)
40 - 60% (Good Removal)
60 - 100% (Excellent Removal)
25 - 40% (Moderate Removal)
40 - 60% (Good Removal)
60 - 100% (Excellent Removal)
Percent TP Removal in Water Body*
This number represents the percent of the total annual mass
of phosphorus entering the water body that is removed.
Cumulative TP Removal in Watershed*
This number represents the percent of the total annual mass
of phosphorus entering the watershed and upstream watersheds
that is removed in the pond and all upstream ponds.
Flow Direction
*Data based on results of P8 modeling.
0 - 25% (Poor/No Removal)
11-11
HopkinsHopkins 169N_16
169N_15
!;N
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4000400
Feet
Figure 11.3
T.H. 169 NORTH
WATER QUALITY
MODELING RESULTS
Comprehensive Water Resource
Management Plan
City of Edina, Minnesota
150 0 150
Meters
Imagery Source: Aerials Express, 2008
25 - 40% (Moderate Removal)
40 - 60% (Good Removal)
60 - 100% (Excellent Removal)
25 - 40% (Moderate Removal)
40 - 60% (Good Removal)
60 - 100% (Excellent Removal)
Percent TP Removal in Water Body*
This number represents the percent of the total annual mass
of phosphorus entering the water body that is removed.
Cumulative TP Removal in Watershed*
This number represents the percent of the total annual mass
of phosphorus entering the watershed and upstream watersheds
that is removed in the pond and all upstream ponds.
Flow Direction
*Data based on results of P8 modeling.
0 - 25% (Poor/No Removal)