Mound Road Ponds Assessment

An Assessment of the Mound Road Ponds

to Determine Optimum Maintenance and
Enhancement Options for Implementation

 

Prepared for the Town of Delavan

 

By
Berrini & Associates, LLC
2701 Seacroft Rd., Springfield, IL  62711
June 26, 2017

 

 

Table of Contents

Introduction.................................................................................................................................. 2

Bathymetric Maps and Pond Cross Sections............................................................................... 6

Current Monitoring Data and Sediment Core Sample Analysis.................................................. 15

Summary and Recommendations............................................................................................... 19

Estimate of Probable Cost........................................................................................................... 21

Alternative Management Options................................................................................................. 23

List of Figures

Figure 1. Location of Mound Road Ponds .................................................................................... 3

Figure 2. Aerial Photo Map of the Mound Road Ponds .................................................................4

Figure 3. Upland Sediment Storage and Dewatering Site  ............................................................5

Figure 4. East Pond Survey Maps ................................................................................................ 6

Figure 5. West Pond Survey Maps  .............................................................................................. 7

Figure 6. North Pond Survey Maps .............................................................................................. 8

Figure 7. Representative East Pond Cross Sections and Locations ............................................ 9

Figure 8. Representative North Pond Cross Sections and Locations  ........................................ 11

Figure 9. Representative West Pond Cross Sections and Locations  ......................................... 13

Figure 10. East Pond Monitoring Map ......................................................................................... 15

Figure 11. North Pond Monitoring Map ....................................................................................... 16

Figure 12. West Pond Monitoring Map ....................................................................................... 16

Figure 13. East Pond Deep Forebay Map .................................................................................. 20

Figure 14. Map of Open Water Area Downstream of Ponds  ......................................................21

Figure 15. Preliminary Sediment Storage and Dewatering Site Plan  ......................................... 22

Figure 16. Floating Wetland Island Images  ...............................................................................  24

List of Tables

Table 1. Sediment Core Sample Analyses ................................................................................. 17

Table 2. Storm Event Monitoring Results ................................................................................... 18

Table 3. Preliminary Estimate of Probable Cost for Mound Road Ponds ................................... 22

Table 4. Pros and Cons of Mound Road Pond Project  .............................................................. 23

APPENDIX

Water and Sediment Depth Contour Maps  ................................................................................ 26

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Introduction

As part of an ongoing effort to protect and improve the water quality of Delavan Lake, the Town of Delavan Lake Committee contracted with Berrini & Associates, LLC to complete an assessment of the Mound Road Ponds to determine optimum maintenance and enhancement options for implementation as recommended in the Delavan Lake Watershed Implementation Plan. The proposed assessment provides the necessary supplemental information to recommend an optimal scope of work for maintaining the ponds, which are existing BMPs. The goal is to continue providing water quality protection for Delavan Lake.

The scope of work included: 1) collecting one sediment core sample from each of the three ponds to evaluate the physical and chemical characteristics of the deposited sediment; 2) obtaining several storm event samples at the inflow and outflow points of each pond; 3) evaluating the results and observations of the assessment, along with existing survey data and reports; and 4) providing recommended maintenance and enhancement options and estimated costs for implementation.

Physical characteristics of the sediment core sample analysis included percent moisture content, bulk density changes with depth and re-mobilization potential at the sediment/water interface. Chemical characteristics of the sediment that are of specific interest for planning include percent organic content and total phosphorus. In addition to sediment analysis, several storm event samples were obtained at the inflow and outflow points of each pond. The collected samples were analyzed for total phosphorus, dissolved phosphorus, and suspended sediment to observe relative pond trapping efficiency. This data was gathered and analyzed along with the recently completed sediment survey measurements (Lake and Pond Solutions, 2015) to determine and recommend maintenance and enhancement options for the ponds.

Selectively removing soft, nutrient-rich sediment from the three ponds to restore lost capacity will be an important component of the overall restoration and maintenance effort. The sediment and nutrient trapping effectiveness of the ponds has been demonstrated by monitoring (USGS, 1995) and by actual survey measurements. The sediment-trapping efficiency of a pond with a given drainage area will generally trap or retain a higher percentage of suspended sediment if the pond volume or capacity is increased. Additional management measures were evaluated to improve the overall effectiveness of trapping and retaining phosphorus within the ponds and wetland system since the USGS study noted that phosphorus was not retained as effectively as suspended solids.

Since dredging is expensive and no grant assistance can be accessed for that purpose (verbal and written communication with WDNR, 2014), it is critical that any sediment removal effort is carefully planned and completed to optimize effectiveness while minimizing environmental impacts and total cost. Therefore, this assessment strategically targets the most cost-effective dredging methods, depths and limits to effectively manage cost while minimizing impacts to the surrounding wetland vegetation. Although grant assistance is not possible for dredging, it may be possible to apply for a grant to implement additional BMPs (such as floating wetland islands, carp management, flocculent logs, biological augmentation, etc.) that would enhance the overall effectiveness of the Mound Road Pond Complex. Potentially, dollars spent on pond maintenance dredging could be used as matching funds for a grant to assist with the implementation of any additional approved BMPs.

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Figure 1.  Location of Mound Road Pond

The Jackson Creek Wetland located immediately north of Mound Road was constructed in 1992 to reduce sediment and nutrient loading to Delavan Lake and to contribute to the long-term protection of lake water quality (see Figures 1 and 2). This shallow prairie marsh approximately 95 acres in size contains three shallow ponds that were excavated to trap nutrients and to improve the overall pollutant filtering effectiveness of the wetland. These ponds, which are commonly referred to as the Mound Road Ponds, are approximately 1.1 acres (West Pond), 1.2 acres (North Pond) and 4.4 acres (East Pond) in size; and collectively receive runoff from sub-watershed drainage areas of approximately 870 acres, 2,778 acres and 5,734 acres respectively. The total watershed area upstream of the pond system is approximately 9,482 acres or 35.6 percent of the entire Delavan Lake watershed. Historical monitoring efforts by USGS have documented that a significant percentage of the sediment and nutrient loadings to Delavan Lake originate from the Jackson Creek watershed. Therefore, the Mound Road Ponds are ideally located to intercept a high percentage of the overall loadings and effectively function as a critical BMP to provide water quality protection for the lake and downstream ecological resources such as the North Inlet.

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Figure  2. Aerial Photo Map of the Mound Road Ponds

When the ponds were constructed in 1992, the storage volume of each pond was approximately 5,719 (West Pond), 5,828 (North Pond) and 12,526 (East Pond) cubic yards respectively based on completed surveys reported by the USGS. From 1993 through 1995 the U. S. Geological Survey (USGS) monitored inflows and outflows to evaluate the function and effectiveness of the wetland ponds to retain sediment and nutrients. Based on the results of this monitoring effort, the ponds were determined to be variably effective at trapping sediment and phosphorus depending on the time of year and the volume of storm water passing through the system. Overall, sediment retention was consistent with a three-year average of approximately 48% with annual averages ranging from 31% to 72% depending on the amount of rainfall that occurred. Generally, the greater the amount of rainfall and associated storm runoff as compared to a normal water year, the lower the percentage of sediment trapped, which is commonly referred to as the trapping efficiency. The average annual percentage of total phosphorus retained in the ponds was approximately 20%, which amounted to 3,440 pounds or 1.72 tons over a three-year period.

The sediment and nutrient control ponds continued to trap and retain suspended sediment and phosphorus from 1995 until 2004 and gradually became very shallow, losing much of their original storage capacity and trapping efficiency. In 2003, the Town was awarded a WDNR Lake Protection Planning Grant (LPL-876-03) to provide partial assistance to complete engineering work for a restoration project at the Mound Road Wetland. From 2004 to 2007, the Town of Delavan obtained permits from WDNR to dredge and excavate accumulated sediment from the East Pond and the

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North Pond to restore their nutrient trapping effectiveness and to protect Delavan Lake from continuing nutrient loading. The West Pond was not dredged at that time since the sediment depths observed were not felt to be significant, most likely due to the smaller watershed drainage area.

Sediment was removed from the North and East ponds and hauled to an approved upland storage and dewatering location near the West Pond to be graded and re-vegetated (see Figure 3). Although an exact sediment removal quantity is unconfirmed, a survey completed in 2013 indicated that total pond volume was increased by deepening the pond bottoms, particularly within 15 to 60 feet from shore. The measured pond volumes to hard bottom (post dredging) were approximately 9,215 CY and 28,040 CY for the north and east ponds respectively. This confirms that the total storage volume of the North Pond was increased by 58.1 percent and the East Pond was increased by 223.8 percent. Although the West Pond was not dredged, the 2013 survey indicated that the measured storage volume was approximately 6,886 CY, which represents a 20.4 percent increase over the 1995 USGS estimates.

Figure 3. Upland Sediment Storage and Dewatering Site


Based on the sedimentation surveys completed in 2013 and 2015 by Lake and Pond Solutions Co., the three ponds were estimated to have lost approximately 33 percent of their total capacity in the eight years since they were cleaned out and deepened. An estimated 14,560 cubic yards of sediment were estimated to have been trapped within the ponds from 2007 to 2015. This confirms that the three ponds have been functioning effectively. However, because of wetter than normal years in 2008 and 2009 combined with several significant rainfall events in the spring of 2013, the three ponds have filled in faster than anticipated.

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Bathymetric Maps and Pond Cross Sections

An updated bathymetric map was developed from water depth measurements measured in 2011 by Krott Surveying, Inc. and then with more current water depth and sediment thickness measurements that were obtained in 2013 and 2015 by Lake and Pond Solutions. The location of each 2015 survey measurement was plotted against the established transect lines and updated maps were developed. Water depth, sediment thickness, and hard bottom depth contour maps were then generated for each pond by manual interpolation methods (see figures 4, 5 and 6 below). The established transect lines and the 2011 bathymetry are shown in Figure 4 (upper left map). Updated maps were developed by plotting 2015 water depth (upper right, Figure 4), hard bottom depth (lower left, Figure 4) and sediment thickness contour maps for the East Pond (lower right, Figure 4). Current water depths ranged from 4.0’ to 5.0’ feet or less through most of the pond with several small areas being as deep as 6.0’ where the deeper perimeter trenches were excavated.

Figure 4. East Pond Survey Maps (full size maps in Appendix)

fig4

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The established transect lines and the 2011 bathymetry for West Pond are shown in the Figure 5 (upper left map), and updated maps were developed by plotting 2015 water depth (upper right, Figure 5), hard bottom depth (lower left, Figure 5) and sediment thickness contour maps for the West Pond (lower right, Figure 5). Water depths ranged from 1.0’ to 6.0’ feet with a small deeper area in the center of the pond and a broad, shallow littoral zone near the outlet. Sediment accumulations ranged from 1.0’ to 2.0’ throughout much of the pond and from 3.0’ to 6.0’ in the center and west end of the pond. The deepest point measured within the pond was 12’ as shown in the West Pond Hard Bottom Depth figure below.

Figure 5.  West Pond Survey Maps (full size maps in Appendix)

fig5

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The established transect lines and the 2011 bathymetry for North Pond are shown in Figure 6 (upper left map), and updated maps were developed by plotting 2015 water depth (upper right, Figure 6), hard bottom depth (lower left, Figure 6) and sediment thickness contour maps for the North Pond (lower right, Figure 6). North Pond water depths ranged from 1.0’ to 5.0’ feet with most of the pond ranging from 3.0’ to 4.5’. Sediment accumulations ranged from 1.0’ to 2.0’ in the center of the pond to 4.0’ and 5.0’ around the perimeter where deeper trenches were excavated and have now filled in. Hard bottom depths ranged from 4.0’ to 6.0’ in the center portion of the pond and 6.0’ to 8.0’ around most of the perimeter with several small areas on the east side of the pond reaching 10’ in depth within the deeper, excavated trench area.

Figure 6. North Pond Survey Maps (full size maps in Appendix)

fig 6

A small number of representative cross section locations were selected to provide a side view of each pond depicting the existing water depth and the extent of sediment deposition. In addition, a dotted red line is plotted on each cross section to represent the approximate water depths observed during the 2011 bathymetric survey. See figures 7, 8 and 9 below

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Figure 7. Representative East Pond Cross Sections and Locations

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Figure 8.  Representative North Pond Cross Sections and Locations

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Figure 9.  Representative West Pond Cross Sections and Locations


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Current Monitoring Data and Sediment Core Sample Analysis

One sediment core sample was collected in 2017 from each of the three ponds to evaluate the physical and chemical characteristics of the deposited sediment. The location of each core sample is shown on the following monitoring plan maps. The samples were obtained on the afternoon of April 12, 2017 using a Wildco hand core sediment sampler with 20” clear CAB plastic liner tubes. The cores were capped and marked top and bottom so the analytical laboratory could analyze the upper and lower half of the sediment cores. A chilled cooler was shipped early the next morning to CT Laboratories in Baraboo, WI. The parameters analyzed were percent solids, bulk density, total phosphorus, total organic carbon, and percent moisture. Although a sieve or particle size analysis was not completed for this project, the sediment was observed to be primarily fine grained silty clay material with relatively low organic enrichment. See Table 1 for a summary of the sediment core sample analyses.

In addition to collecting sediment core samples, two separate storm event samples were obtained at the inflow (inlet) and outflow (outlet) points of each pond (see figures 10, 11 and 12). The water samples were collected on September 22, 2016 and October 26, 2016 and shipped to CT Laboratories for analysis. Total suspended solids (TSS), total phosphorus (TP), and orthophosphate or soluble reactive phosphorus (SRP) were analyzed by the lab. During the September 22, 2016 storm event, two separate grab samples were obtained two hours apart and analyzed separately.

Figure 10. East Pond Monitoring Map

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Figure 11.  North Pond Monitoring Map

Figure 12.  West Pond Monitoring Map

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Sediment core sample analysis showed variations from pond to pond and from top of core to bottom of core. A full 20” core was obtained from each location; the top and the bottom of each core represented a 10” section. An aqueous, flocculent layer was observed at the sediment/water interface, and the core sampling device allowed excessively flowable material to escape from the top flap valve, thus encapsulating a more solid sediment sample. The sediment in all three ponds became denser with depth, likely from consolidation over time. In East Pond, the percent solids increased from 51.9% in the upper 10” to 66.4% in the lower 10” section; bulk density increased from 53.7 lbs/cf to 86.2 lbs/cf. Higher density sand was observed in the lower section of the East Pond core sample. The percent solids in West Pond increased from 25.5% at the top of the core to 42.2% at the bottom; bulk density increased from 24.4 lbs/cf to 72.4 lbs/cf. The sediment in West Pond was primarily fine grained silt and higher in organic content than East Pond or North Pond. In North Pond, percent solids increased from 48% at the top to 54% at the bottom; and bulk density increased from 43.7 lbs/cf to 54.9 lbs/cf. Total phosphorus in East Pond was 1,010 mg/kg at the top and 491 mg/kg at the bottom. West Pond phosphorus was 1,450 mg/kg at the top and 1,030 at the bottom and North Pond phosphorus was 1,030 mg/kg at the top and 1,020 mg/kg at the bottom.

Table 1. Sediment Core Sample Analyses

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The average bulk densities were: 70.0 lbs/cf for East pond, 48.4 lbs/cf for West Pond and 49.3 lbs/cf for North Pond and the average phosphorus concentrations were 750 mg/kg for East pond, 1,240 mg/kg for West Pond and 1,025 mg/kg for North Pond. The identified soft sediment dredging volumes are approximately and 10,439 cubic yards for East Pond, 4,292 cubic yards for North Pond and 1,699 cubic yards for West Pond. The estimated tons of sediment that will be removed are 9,759 for East Pond, 2,786 for North Pond and 1,103 for West Pond; and the estimated pounds of phosphorus to be removed are 14,828 for East Pond, 5,863 for North Pond and 2,741 for West Pond. Based on this analysis of estimated sediment and phosphorus removal, a total of 13,648 tons of sediment and 23,432 pounds of phosphorus will be removed from the three Mound Road ponds during the proposed maintenance cleanout effort.

The collected storm event water inflow and outflow monitoring data are summarized in Table 2 below. The results were variable with all ponds generally showing a positive sediment and phosphorus reduction between inflow and outflow. However, during the October 26, 2016 event, East Pond showed higher concentrations of suspended solids and phosphorus leaving the pond than coming in. This may have resulted from the higher flows typical of the much larger Jackson Creek drainage area where agitation and re-mobilization may have occurred due to high flow velocities. Numerous common carp were also observed on multiple occasions and may have contributed to added turbidity and phosphorus release.

Table 2. Storm Event Monitoring Results

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Summary and Recommendations

The Mound Road Ponds have been very effective sediment and nutrient traps since they were constructed. In the 10 years since the North and East Ponds were cleaned out in 2007, approximately 4,292 and 10,439 cubic yards of sediment respectively have been retained. These sediment volumes represent 41% and 29.6% of the total pond volumes for North and East Ponds. Although West Pond was not dredged at the time, it has retained 1,699 cubic yards or 45.6% of the total pond volume. It is recommended that all accessible soft sediment is removed by hydraulic suction dredging from the three ponds, which is estimated to be approximately 16,205 cubic yards (measured in-situ). It is important to remove as much soft sediment as possible to maximize overall pond capacity, water depth and cross sectional area, which will reduce flow velocity and minimize re-mobilization of soft, flocculent nutrients at the sediment-water interface.

The representative cross sections show a dashed red line that represents the bathymetry or water depths of the three ponds from the 2011 survey (see figures 6, 7 and 8). It is evident that visible sediment accumulation has occurred in North Pond and West Pond between 2011 and 2015, whereas the sediment in East Pond has changed very little in the same four years. This may mean that East Pond had already reached a condition that warranted cleanout and maintenance. The highest loss of storage volume in East Pond was between the inflow and outflow points of the pond. Lesser reductions in storage volume were observed in the southwest corner of the pond and outside of the direct inflow/outflow path. This area of the pond may become more effective if an outlet channel were installed to allow for a more efficient flow path from inlet to outlet and to reduce short circuiting. However, an additional or alternate outlet channel would require concurrence with WDNR for conceptual and regulatory approval.

The cross sections show that the deeper perimeter trench that was excavated around much of East Pond has been effective at trapping sediment. However, once sediment deposition has reached its effective limit, less settling occurs. Shallow water and periodically high flow and/or high wind conditions can cause loose sediment and nutrients to be re-mobilized and transported further downstream. Since East Pond receives direct runoff from a large drainage area and is subject to higher flows from Jackson Creek, a deep forebay area situated outward from the entry point in the east half of the pond would reduce incoming flow velocities and would allow more effective settling to occur for a longer period between maintenance cleanout cycles (see figure 13 below).

The hard soil material underlying the accumulated sediment in the shallow shelf portion of East Pond has been determined to be a gravelly glacial till. Therefore, selective deepening will likely require mechanical excavation to effectively remove the underlying material to an approximate 10 foot depth, similar to the surrounding perimeter trench depth. This approximate 0.75 acre deepened forebay would include the removal of approximately 4,000 cubic yards of hard underlying material separately from the soft accumulated sediment within the pond. This gravelly material may be hauled to the designated placement site or it could potentially be used to augment a portion of the East Pond access road, which is frequently wet or flooded.

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Figure 13. East Pond Deep Forebay Map


Although this assessment has focused on the three ponds that were constructed to trap and retain sediment and nutrients upstream of the lake and to provide long term water quality protection for Delavan Lake, there has been no data gathered in the open water area directly upstream of the Mound Road Weir. The outflow from all three ponds discharge directly into this open water area prior to flowing over the weir and then into the North Inlet. It is recommended to include a similar water depth and sediment depth survey to assess current conditions and to evaluate whether this active flow through area may require any maintenance due to accumulated sediment and similar loss of water depth. This recommended survey and assessment is estimated to cost $8,000 to $10,000 and should be considered for future planning and implementation (see Figure 14).

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Figure 14. Map of Open Water Area Downstream of Ponds

Estimate of Probable Cost

If the 16,200 cubic yards of identified soft sediment are dredged, the estimated cost of completing maintenance cleanout requirements for the Mound Road Ponds is preliminarily estimated to be approximately $530,600.  The cost would include regulatory permitting, engineering design, site erosion control, sediment removal, and monitoring (see Table 3 below).  Maintenance cleanout would essentially restore the functionality of the ponds to effectively trap and retain suspended sediment and phosphorus.  However, cleaning out accumulated sediment is dredging and is not an activity that re-qualifies for WDNR grant money.  Preliminary discussions with WDNR have indicated a grant application focused on implementing nutrient reduction BMP's.  An additional recommended task that  has been identified includes surveying and assessing the open water area directly downstream of the three ponds and immediately upstream of Mound Road at an estimated cost od $10,000.  This task would determine whether shallow water depts. and sediment accumulations are contributing  to downstream nutrient loads and whether maintenance is required.

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Table 3. Preliminary Estimate of Probable Cost for Mound Road Ponds

Description Units Unit Cost Total Cost
Engineering and Permitting 1 LS $45,000 $45,000
Temporary Erosion Control 1 LS $10,000 $10,000
Mobilization & Site Prep 1 LS $50,000 $50,000
Dredging and Dewatering – Hydraulic* 16,200 CY $18.00 CY $291,600
Deep Forebay Excavation 4,000 CY $25.00 CY $100,000
Forebay Material Hauling 4,000 CY $6.00 CY $24,000
Post Dredge Survey 1 LS $10,000 $10,000
Total Estimated Project Cost $530,600


* Hydraulic dredging with geotextile tubes for dewatering soft sediment is recommended

The 16,200 cubic yards of soft sediment would be pumped via HDPE dredge pipeline to the designated sediment storage and dewatering area used in 2007 and approved by WDNR (see Figure 15 below). The excavated gravely till could either be hauled to the designated storage area or could potentially be used to augment and improve the access road to East Pond, if approved, since it is low in elevation near the pond and often very wet or ponded.

Figure 15. Preliminary Sediment Storage and Dewatering Site Plan
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The following Table 4 summarizes the pros and cons of the proposed Mound Road Pond Maintenance Project, along with an estimated cost of sediment and phosphorus removal (per ton and per pound respectively) over a 10-year period when maintenance would likely be required.

Table 4.  Pros and Cons of Mound Road Pond Project

Dredge Mound Road Ponds Pros Cons
Estimated Cost: $530,600 plus contingency; the restored ponds would trap approx. 1,365 tons of sediment and 2,343 pounds of phosphorus annually. Over a 10-year maintenance period, the estimated total cost of nutrient reductions would be approx. $38.90 per ton of Sediment and $22.65 per pound of Phosphorus

 

 

·         Improved water quality

·         Intercepts sediment & nutrients from large watershed

·         Documented lake protection

·         Opportunity for potential grant assistance with non-dredging pond system enhancements and watershed BMP planning and implementation

·         Sediment removal will provide benefits at higher cost due to grant exclusions for dredging

·         Optimum lake protection will require additional watershed BMPs due to large drainage area size

·         Future maintenance to remove sediment will be required for continued effectiveness


Additional Management Options

An additional BMP that can improve nutrient trapping effectiveness and reduce sediment and phosphorus loadings to Delavan Lake includes the design and installation of floating wetland islands (see sample photos below) within the existing ponds. The floating wetland islands would enhance nutrient trapping effectiveness by increasing pond retention time and minimizing inflow short circuiting to the pond outlets by using ballasted baffle curtains under each island. Nutrient uptake during the spring, summer and fall seasons would also occur via native plant root systems extending downward into the shallow water column. The size and configuration of the anchored islands would be completed prior to installation and management. It is important to note that if this option is implemented, secure anchoring of the floating islands is critical and that periodic maintenance will be required. This BMP may potentially qualify for grant assistance if costs incurred for sediment cleanout were applied as matching funds. Preliminary estimates for designing, installing, maintaining and monitoring are conceptually estimated to be approximately $80,000 to $100,000 plus a 20 percent contingency. However, as noted above, the islands may potentially become moved or impacted by storm flows and will likely require periodic retrieval and re-anchoring based on other observed installations.

Selective carp removal from the ponds and surrounding areas upstream of the Mound Road weir is strongly recommended. On many occasions, numerous common carp have been observed in these areas, particularly in East Pond and North Pond. Increased carp populations can contribute to nutrient loading by re-suspending bottom sediments and phosphorus and can reduce aquatic plant density, which is critical for filtering incoming nutrients. This action was also recommended in the Delavan lake Watershed Implementation Plan as a management alternative for the North Inlet. The Town has indicated that WDNR is willing to assist in carp management, but preliminary indications are for carp removal efforts from within Delavan Lake. Additional carp removal efforts should also be focused on the Mound Road Ponds and other open water areas upstream of the Mound Road weir.

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Figure 16. Floating Wetland Island Images

Additional alternatives and treatments that have been considered include Floc Logs and bio-augmentation with aerobic bacteria and enzymes. The Floc Logs and Pond Logs are a product manufactured by Applied Polymer Systems, Inc. (APS) and utilize anionic polymers to floc out (settle) suspended solids and phosphorus within the water column. However, according to the manufacturer, this product works most effectively when there is flowing water around the logs either with an aerator or other circulating system. Flowing runoff water into the ponds may be sufficient to activate or release the anionic polymers, but high flows may also overwhelm the logs and require regular maintenance and replacement.

Since the product contains a regulated polymer, regulatory approval would be required and the cost of replacement and maintenance must be considered. Manufacturer’s literature indicates the pond logs can treat 325,000 to 500,000 gallons of water. The smallest of the ponds is West Pond at 1.1 acres with a volume ranging from 400,000 gallons (existing conditions) to 750,000 gallons (after cleanout), plus significant inflow during storm runoff events. Therefore, two or three properly

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matched pond logs should be capable of effectively treating West Pond. North pond is larger and ranges from 1.3 to 2.1 million gallons plus storm water inflow and East Pond being considerably larger and ranges from 5 to 7 million gallons plus significantly greater inflow during storm events. The manufacturer suggests that pond logs would typically be replaced approximately once per month except during winter. Online prices have been listed at $200 per pond log. Therefore, if applied after West Pond is cleaned out, approximately 3 pond logs would be replaced at least 8 times per year at approximately $5,400 per year, plus any labor and costs that would be required. After cleanout, North Pond and East Pond would require approximately 8 to 20 pond logs respectively each month for an estimated 8 months per year at an estimated cost of $12,800 to $32,000 annually for North and East Ponds respectively. While this product is worth considering for smaller applications, the Mound Road Ponds, except for West Pond, may be too large of a system to obtain cost effective results.

Introducing aerobic bacteria and enzymes is another alternative that has been considered for sediment and phosphorus management in the ponds. Normally “bio-augmentation” is most effectively utilized to treat organically enriched sediment in conjunction with a properly designed aeration system. Recent test installations have indicated that some positive results may be attained, such as improvements to water quality. However, the sediment in the ponds were found to contain an average organic content of 3 to 8 percent, with East Pond being the lowest and West Pond being the highest. Therefore, significant sediment reductions resulting from aeration and bio-augmentation are not possible. Any pilot testing effort to utilize bio-augmentation should be considered only as a post-cleanout management tool for future evaluation. Therefore, this alternative is not recommended for any initial pond restoration efforts as it has not been proven to eliminate or significantly reduce excessive sediment deposition.

One additional management option to consider for future maintenance, once the ponds have been completely cleaned out, would be to more frequently remove soft, accumulated sediment using small scale auger or diver operated dredging methods to minimize the magnitude of long term cleanout projects and to maximize the trapping effectiveness of the ponds. This process would be considered pro-active maintenance and is recommended.

Continuing to reach out to upstream landowners and implementing best management practices throughout the Upper Jackson Creek sub-watershed, as recommended in the Delavan Lake Watershed Implementation Plan, will also reduce sediment and nutrient loads and will help to optimize and extend the effectiveness of the Mound Road Ponds after maintenance cleanout cycles.

 

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APPENDIX

Water and Sediment Depth Contour Maps

East Pond

Transect Location Map Bathymetric (Water Depth) Map Hard Original Pond Bottom Map Sediment Thickness Map

North Pond

Transect Location Map Bathymetric (Water Depth) Map Hard Original Pond Bottom Map Sediment Thickness Map

West Pond

Transect Location Map Bathymetric (Water Depth) Map Hard Original Pond Bottom Map Sediment Thickness Map

 

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