1
Restoration of Ecosystem Services:
A Plan to Minimize Filling of Manitou Stream
by the
Adaptive Restoration Task Force
of the UW-Madison Arboretum
12 March 2010
Minimum-grading-and-fill option to fulfill Chapter 30 and the Clean Water Act
Negotiated alternative option with an upstream stormwater retention pond, a channel
terrace, and Secret Pond unaltered
This document is intended to be used in conjunction with the longer, 19 February 2010
version of the Manitou Stream Plan. The longer document contains the context,
appendices, and literature cited.
2
Executive Summary
Manitou Stream and adjacent wetlands are protected waters of the State and the
US, and plans for modification involving filling of waters or wetlands need to be
permitted after analysis of alternatives that would avoid, minimize and/or compensate
for fill. These protections are consistent with the Arboretum’s stormwater management
values and principles.
The 635-foot-long Manitou Stream has experienced “urban stream syndrome”
(increased stormwater inflows, incised channel, dewatered floodplain, and reduced
ecosystem services). Denitrification is especially constrained in urban streams, and
Arboretum wetlands are negatively affected because the nitrogen in stormwater
stimulates the growth of invasive weeds, especially reed canary grass. Nitrogen can
also cause algal blooms in downstream lakes.
Ecosystem services could potentially be restored without substantial filling of
waters or wetlands and without loss of buried wetland soil. Toward that aim, ARTF
proposes a restoration plan that would provide multiple ecosystem services by
removing some accumulated sediment along the stream edge, facilitating denitrification
on the new floodplain, stabilizing the floodplain and vertical streambanks with
coppiced tree willows, and potentially stabilizing the stream bottom.
The aim is broad, namely to rehabilitate the area from Manitou Way to Lake
Wingra to restore multiple ecosystem services by providing natural landscape features,
improving habitat for native plants and animals, accommodating inflowing sediments,
reducing eutrophication of Arboretum lands, reducing channel erosion, accumulating
sediment where it is needed—in the streambed, where it would elevate the topography
and reduce dewatering of the floodplain, thereby enhancing denitrification. In addition,
we aim for a holistic system that will attract members of the community to participate
in stream rehabilitation and long-term sustainability.
Contents
1. Minimum-grading-and-fill option is excerpted from the Plan to fulfill Chapter 30 and
the Clean Water Act
2. Negotiated alternative option with an upstream stormwater retention pond, a channel
terrace, and Secret Pond unaltered
Background
Surface-water runoff exceeds historical levels due to hardscape (asphalt, concrete)
covering large proportions of urban watersheds, lawns that lack deep-rooted plants, and
compacted soils that reduce infiltration. With more runoff and higher peak storm flows,
3
Manitou Stream has experience a suite of conditions known as “urban stream syndrome”
involving channel incision and bank erosion, and the adjacent floodplain has experienced
lowered water tables, reduced soil moisture, reduced denitrification potential, and
conversion of vegetation to plant species that are less flood tolerant than those that might
have been present prior to urbanization. The Manitou Stream and its former floodplain is
such an example.
Manitou Stream
The Arboretum’s Adaptive Restoration Task Force (ARTF) considers the channel
that carries urban runoff under Manitou Way and into the Arboretum to be an urban
stream (herein called Manitou Stream). It has the “urban stream syndrome” (channel
incision, bank undercutting, bank sloughing, and erosion of sediments) due to its
developed watershed. Stormwater inflows to Secret Pond (modeled to be 513 acre-feet
per year) are the largest of all nine inflows to the Arboretum. Manitou Stream flows
through 650 feet of incised channel, and the lowest elevation of the streambed occurs
within Secret Pond, which has mostly filled in with inflowing sediments.
Water flows through Secret Pond and into the marsh downstream, where it is
joined by water from the Nakoma Gulf Course Stream and then into Lake Wingra. At the
shore of Lake Wingra, sediment from one or both streams accumulates and forms islands
that gradually become vegetated. ARTF has designed a water-quality monitoring
program to evaluate particulate and dissolved materials that are of concern to managers
of the Arboretum and Lake Wingra, e.g. phosphorus and nitrogen, which stimulate weed
invasions in Arboretum wetlands (Green and Galatowitsch 2002, Boers and Zedler 2008,
Kercher et al. 2007) and cause eutrophication, leading to algal blooms (Lathrop 2007,
Carpenter 2008, Lewis and Wurtzbaugh 2009).
An important role for UW
The University could play a unique role in demonstrating how best to manage
stormwater. Others look to UW for leadership in multi-disciplinary policy/decision
making and innovation in technology and conservation. They look to the Arboretum for
leadership in restoration and land care. The need to improve stormwater facilities within
the Arboretum provides many opportunities for innovation, research, and education..
Note that biological systems are inherently complex, and detailed predictions are
always challenged by unknowns. There are several unknowns in the in the stormwater
management arena and for stormwater treatment options. Other unknowns have been
identified for the “Best Management Practice” of creating a large stormwater retention
basin, e.g. therole of impoundments as habitat for mosquitoes (Irwin et al. 2008),
“magnets for invasive species” and “stepping stones” for the dispersal of invasive species
from those impoundments to natural lakes and ponds (Johnson et al. 2008. The
Arboretum follows an innovative adaptive restoration approach for situations where there
is insufficient knowledge to guarantee outcomes of alternatives.
1. Minimum-grading-and-fill option
to fulfill Chapter 30 and the Clean Water Act
4
Ecosystem services are ecological functions that are valued by society. Wetlands
(including shallow waters to 6 m depth, as defined by the Ramsar Convention
[international treaty]) provide disproportionate levels of annually renewable ecosystem
services. Using data of Costanza (1995), wetlands covering 1.5% of the earth contribute
40% of ecosystem services globally—26 times the per-area contribution from uplands
and oceans.
Goal: The Arboretum needs to fulfill its mission (to conserve and restore the
land, advance restoration ecology, and foster the land ethic) as well as comply with
stormwater regulatory requirements. The aim is broad, namely to rehabilitate the area
from Manitou Way to Lake Wingra to restore multiple ecosystem services by providing
natural landscape features, improving habitat for native plants and animals,
accommodating inflowing sediments, reducing eutrophication of Arboretum lands,
reducing channel erosion, accumulating sediment where it is needed—in the streambed,
where it would elevate the topography and reduce dewatering of the floodplain, thereby
enhancing denitrification. In addition, we aim for a holistic system that will attract
members of the community to participate in stream rehabilitation and long-term
sustainability.
This Restoration Alternative would create conditions to support ecosystem
services associated with historical streams, their adjacent floodplains and wetlands,
without filling wetlands or waters of the US.
Why not a focus on restoring historical vegetation? Given that Manitou Stream
carries water that is greater in volume and lower in quality than occurred naturally, and
given that the land adjacent to the stream has accumulated tons of sediment overlying its
wetland soil, historical conditions could only be restored with heroic efforts to replumb
the watershed, then excavate and transport sediments off-site. In addition, the Arboretum
is required to maintain a specific one-acre stormwater retention facility, namely, Secret
Pond, which is a novel landscape feature. Novel approaches for transforming degraded
and altered landscapes recognize the dynamic nature of both restored and reference
ecosystems, as well as the need to address both structure and functioning (Ewel and Putz
2004, Suding, Gross and Houseman 2004, Harris et al. 2006, Zedler 2009, Seastedt,
Hobbs and Suding 2008, Jones and Monaco 2009).
Why a focus on ecosystem services? A principal reason for focusing on functions
instead of specific plant or animal species is the high value and importance of ecosystem
services to downstream ecosystems. A feasible goal is to restore ecosystem services that
have been lost within the watershed; thse include phosphorus- and sediment-removal
services, as well as floodplain habitat, denitrification, and cultural services.
Ecosystem services that are especially needed are:
5
• Reduction of nitrogen loading to Arboretum wetlands and Lake Wingra
• Reduction of phosphorus loading to Arboretum wetlands and Lake Wingra
• Erosion control
• Reduction of floodplain dewatering
• Biodiversity support
• Resistance to invasive plants
Location: Existing stream and adjacent wetland and upland between Manitou
Way and Secret Pond (the existing stormwater retention pond that is filled with
sediment), with consideration of additional ecosystem services occurring within Wingra
Marsh and along the Lake Wingra shore. Arboretum lands at this site include the
Manitou Stream, its riparian woodland, west Wingra Marsh, and the shore of Lake
Wingra.
Manitou Stream has a lower, 350-ft stream segment and an upper 285-ft stream
reach that would be supplanted by a 2.43-acre stormwater retention basin in other
alternatives designed by Strand Engineering. The total length of the stream, from
Manitou Way to Secret Pond is 635 feet. An estimate of the proposed restoration project
footprint is 0.84 acres. This would include 0.84 acres of proposed floodplain restoration
and 0.30 acres of existing sream bottom, i.e., 0.54 acres.
Historical sediment delivery: The study experienced major sedimentation in past
decades, followed by lowering of the water table (Pathak 2009). Soil profiles nearest the
stream indicate that 27-48 inches of recent soil overlies a buried organic soil just north of
the existing stream (Table 1). Substantially more data on the depth to organic soil are
needed to develop a plan to remove accumulated sediments and not disturb the
underlying wetland soil. We recommend 10 transects from each stream edge inland to
the limit of proposed excavation, with 1-inch cores taken at 2- to 5-m intervals along each
transect, assessing depth to organic soil.
Table 1. Depth of sediment overlying organic soil at west Wingra Marsh (from Pathak 2009).
Well
number
Depth of surface
sediment (inches)
North of stream
1
2
8
9
30
27.5
48
27
South of stream
14
15
23
0-12
0-13
0-12
6
Figure 1. Current vegetation as mapped by Pathak (2009).
Recommended actions to restore ecosystem services
• Open the canopy along the stream course to increase light (to enhance willow growth)
• Partially remove sediment that overlies the buried wetland soil
• Promote denitrification on the floodplain
• Stabilize the floodplain sediments with roots (tree willows planted on the floodplain)
• Coppice the tree willows to avoid windthrows; remove biomass when P content is high.
• Stabilize the streambanks and streambed edge with sandbar willows
• Consider widening the thalweg to accommodate roughness due to sandbar willow
• Stabilize stream bottom sediments with fieldstone crossings
• Allow sediments to accumulate and elevate the streambed to slow floodplain
dewatering; allow phosphorus to be stored in the stabilized sediment
• Excavate most accumulated sediment in Secret Pond
• Retain the vegetated island at the mouth of the stream in L. Wingra
• Provide cultural services, including uses of harvested willow twigs and poles.
We propose to advance restoration ecology by incorporating small experiments
into the plan to test the use of native willows in stabilizing the floodplain (e.g., varying
planting density and coppicing frequency), shallow pools of varied size to remove
nitrogen, and sandbar willow to stabilize the streambanks and streambed edges. The
science/practice of “adaptive restoration” is also advanced by initiating field experiments
that provide guidance for subsequent restoration efforts. Field tests of understory
plantings would also be possible on the floodplain. Studies of soil stabilization,
7
stormwater infiltration, arthropod use, bird use, and biofuel production could also be
supported by the following restoration project.
Figure 2. The 0.84 project footprint above Secret Pond. Areas include the 0.30-acre stream bottom (of
which 0.12 ac are in the upstream segment and 0.18 ac are in the downstream segment). The upstream segment is
the portion that would be covered by a stormwater retention basin in alternatives designed by Strand Engineering.
Figure 3. Cross-section for Manitou Stream showing recently-deposited sediment to be removed,
underlying buried wetland soil to be conserved, willow posts to be planted on the resulting floodplain, and
willow poles to be planted in segments of the stream. Depressions that would pond water after overbank
flooding are not shown in these cross-sections. This alternative has willows on a graded south-facing
streambank and a widened streambed (width not determined), Fieldstone crossings about every 60 linear
feet are under discussion. Illustrations by M. Wegener.
8
Figure 4. Overview possible floodplain alongside Manitou Stream, showing a widened
streambed (crudely estimated), a sloped north side of stream with sandbar willow
plantings to stabilize the bank, with the south bank left intact. Illustration by Mark
Wegener, with input from Jim Doherty and Brad Herrick.
9
Explanation of each action
Opening the canopy to increase light. Prior to excavation, trees would be
selected by ARTF for removal in each 18-ft-wide strip along Manitou Stream.
Additional trees would be removed on the south side of the stream to open the canopy
and increase light to enhance willow growth. Removal would be selective in order to
retain heritage trees or trees considered important for ecosystem services, such as soilholding capacity.
Partial sediment removal: We propose to remove existing trees along a narrow
strip next to Manitou Stream and then to remove some of the sediment that has
accumulated over decades, leaving 12 inches above the buried wetland soil. While a
large area could be deforested and graded, costs will likely limit the effort. The area of
sediment removal could be under 0.5 acres. It could be evenly divided to two 15 x 600-ft
strips, one to the north and one to the south of Manitou Stream. Assuming an average
depth of removal of 1 foot, the volume of sediment to move could be 0.5 acre-feet (807
cubic yards for the smaller estimate). The remaining streambank will be left intact; i.e., it
will not be graded. Note: ARTF still needs to consider the regulations about grading and
the permits needed.
Promoting denitrification on the floodplain: Floodplain contouring would support
diverse understory vegetation and trap overbank flows in shallow ponds. Providing a
variety of sizes and depths of depressions will allow pools to develop following
stormwater pulses with overbank flooding. These pools are intended to provide the
valued functions of unfiltration and denitrification. The principal factors that promote
denitrification are moisture (enough to create anaerobic conditions) and root biomass
(which provides organic matter to the rhizosphere, where microbes use it as food during
denitrification). Fine-textured soil (silt and clay) on the floodplain helps to retain soil
moisture (Pinay et al. 2000). Shallow pools and an understory of native plants known to
produce both shallow and deep roots (Botany 670 experimentation) will promote
conditions that enhance denitrification potential in restored urban streams (Gift et al.
2010). Soil probes would be used to identify depth to organic soil so that the volume and
location of excavation can be estimated.
Streambank and floodplain stabilization: Tree-willow posts will be established on
the excavated floodplain to stabilize the floodplain soil (see also Barendregt et al. 2009).
Herbaceous understory plantings of native species known to provide ecosystem services
would further reduce erosion, assist in infiltration and resist invasion by wetland weeds.
Suitable species to plant and planting approaches are described in appendices. Note that
black willow occurs north of Secret Pond (B. Herrick, from Botany 455 class data).
Willow post densities will be established at two levels in an experimental framework.
Streambanks will be stabilized in part by roots that will grow from willow poles
or posts installed along the stream channel on the floodplain. In addition, sandbar willow
stakes will be placed within the banks as described after coppicing.
Herbaceous vegetation will be provided to enhance infiltration (and
denitrification), reduce soil erosion, and resist weed invasion. Herbaceous understory
10
species suitable for seed mixes (described in future appendices). Note that willow
plantings might also reduce reed canary grass invasion (Kim et al. 2006).
Streambed stabilization: Manitou Stream is subject to pulses of stormwater that
can flow up to a maximum of 300 cubic feet per second (cfs), limited by the size of the
culvert under Manitou Way. Down-cutting of the outfall at Manitou Way is reduced by
riprap and boulders that were recently put in place within the Arboretum. Further downcutting along the entire Manitou Stream (and resulting undercutting of stream banks)
could be abated using willow plantings, fieldstone crossings, and/or large woody debris.
Large woody debris is a common stream restoration practice, and it is particularly
valued for its ability to provide habitat for macroinvertebrates (Miller et al. 2010).
Because large trees will be removed along the edges of Manitou Stream, there will be
opportunity to place trunks in the stream strategically to achieve such functions. More
study of the extensive literature on ecosystem services provided by various uses of large
woody debris is needed to develop specific plans for such addition.
Fieldstone crossings would be used to divide Manitou Stream into six to ten
stream reaches. Large stones could be placed across the stream as in the Pike Creek
project in a Minneapolis suburb (MacDonagh and Ryan 2009). Pike Creek statistics are
quite similar to those of Manitou Stream. For Pike Creek, the watershed area = 465
acres, impervious surfaces = 35-50%, project length = 1,600 feet, project width = <120
feet, maximum bank depth = <8 feet, maximum water depth = <7 feet, width = 10-12
feet, soils along channel = Hamel Loam and Heyder Sandy Loam, channel gradient =
1.5%, flow range = 0-800 cfs, maximum velocity = <9 fps (from MacDonagh and Ryan
2009). If 6-10 stream crossings (one per 60-ft or 100-ft stream reach) are established
(each crossing @ 3 x 10 ft. = 30 sq. ft.), the area of fieldstone fill will total 180 sq. ft. for
5 crossings (6 segments) or 270 sq. ft. for 9 crossings (10 segments). Adding sandbar
willows along the streambank edges within the fieldstones would anchor the fieldstones.
Sediment erosion or accretion will be assessed and test plots expanded or replanted
accordingly. The plantings are described in detail below.
Sandbar willow stakes would be inserted into both streambanks along the entire
stream, using standard staking approaches. Willows will be planted in a pilot phase,
followed by later plantings, based on earlier results. If plantings are done prior to a rain
storm and streamflow pulse, it is possible that the poles that have not established solid
rooting will wash out, even though sandbar willows are known for their flexibility (Alice
Thompson, pers. comm. 2009). ARTF is prepared to reestablish sandbar willow plots if
poles need to be replaced. Curtis Prairie has an overabundance of sandbar willows, and
poles are easily harvested and relocated.
Maintaining Secret Pond: DNR regulations require that existing stormwater
facilities be maintained. Secret Pond has accumulated substantial sediment, although the
stream continues through it and discharges into a cattail marsh. The downstream portion
of Secret Pond still holds water and supports native wetland vegetation, including
arrowhead, rice-cut grass and common bur-reed (2006 survey by Steven Hall). This
wetland vegetation likely filters surface water flow and potentially reduces transport of
TSS to Lake Wingra.
11
The constructed volume of the pond is not known, but if estimated to be an acrefoot, around 1600 cubic yards of accumulated sediment would need to be excavated.
Removing accumulated sediment would be done in winter, to reduce impacts on soil and
vegetation. Sediment will be moved off-site to prevent re-release of contaminants and to
avoid construction of mounds or berms elsewhere on-site. The northeastern tip of the
pond should be left intact, as it is still functions as a wetland with native vegetation.
Prior to excavation, historical records of the depth and location of the excavation
for Secret Pond will be consulted and not exceeded in removing the accumulated
sediment. Care will be taken to leave the pond bottom and edges sealed where they abut
wetland soil so that underlying peat is not disturbed or removed.
To stabilize the disturbed banks, sandbar willow plantings would be extended
from Manitou Stream around the edges of the excavated portion of Secret Pond.
ARTF recommends that accumulated sediments be excavated during winter to
reduce impacts of heavy equipment on the adjacent wetland soil and vegetation.
Providing cultural services: Research, education, and passive recreation will be
promoted by experimental willow plantings and depressions on the floodplain (see
following section).
ARTF envisions that local neighbors and Friends of the Arboretum might adopt
segments of the restored stream for restoration and maintenance. The “Adopt-a-StreamReach” program could attract donations for fieldstones, volunteers to install sandbar
willows, volunteers to monitor establishment and growth of willows, volunteers to
harvest willow twigs and poles, and volunteers to assist with research.
Passive recreation (bird watching, hiking) would be facilitated by trails that would
also be used by those who coppice the tree willows. Trails are inevitable, so it would be
prudent to establish routes that will benefit project maintenance. To reduce liability
issues, signs will be placed to keep visitors on trail, cautioning that fieldstones are
slippery, rapidly-flowing streams are dangerous, and wetland soil can trap boots.
Planning for new signage would benefit from public involvement (Figure 8).
“Foster Parents” of the adopted stream reaches could post their activities and contributors
and use signs to keep track of areas restored and ecosystem services provided. They
could also contribute news and data to the Arboretum’s interactive web site.
2. Negotiated alternative option
with upstream stormwater retention pond, channel terrace, and Secret Pond unaltered
The above Restoration Plan would not generate stormwater credits for the
municipalities who have helped fund other stormwater retention basins in the Arboretum.
Here, we consider the trade-off of combining a stormwater retention pond upstream of a
restored stream. This option would not avoid filling caused by the installation of an inline pond, because the berm would cross Manitou Stream, and sediments would
accumulate inside the berm and fill the existing stream channel. Previously, Strand
Engineering designed a 2.43 stormwater retention basin for Manitou Way that also calls
for complete grading of the banks of Manitou Stream with turf-reinforcement matting for
the remaining 300 ft of Manitou Stream, amounting to additional fill. In addition, Secret
12
Pond is excavated but bank stabilization measures are uncertain. Collectively, their pond
and stream projects greatly exceed 10,000 sq. ft. of grading and filling. Permitting issues
need to be considered.
If a pond is agreed upon and permitted, there are still opportunities to minimize
filling in Manitou Stream downstream of the pond. Instead of armoring the 300 ft length
of streambanks, ARTF recommends a downscaled version of the above Restoration
Alternative, to learn how willows can stabilize streambanks and streambed edges.
ARTF recommends avoiding or minimizing changes to Secret Pond in exchange
for accepting a conventional stormwater retention pond at Manitou Way. Presumably,
this would involve a variance from DNR to leave some sediment in place in Secret Pond,
in order to allow a shallow-pond system to support wetland vegetation and improve water
quality.
We would plan to use willows to stabilize the banks of any grading in or around
Secret Pond.
Employing the stream restoration in an adaptive manner would allow ARTF to
test effectiveness of willows in streambank and pondbank stabilization before full-scale
implementation of the combined pond/stream modifications.
The decision-making process
ARTF recommends improving the process of achieving consensus.
The Stormwater Committee should be apprised of regulatory constraints, allowed to hear
a description of this plan, and be given ample opportunity to understand multiple viewpoints to
discuss alternatives face-to-face. If consensus is not achieved, multiple viewpoints and rationales
should be presented to the Arboretum Committee.
The Arboretum Committee should understand the requirements for permitting,
acknowledge the potentially conflicting regulations and agreements, and objectively weigh the
pros and cons of alternative plans. The Arboretum Committee should be asked to provide a
policy statement on the relative merits of alternatives that avoid, minimize and compensate for
negative impacts to Arboretum lands. They would need to read this plan to obtain essential
background information.
Initial discussion with Cami Peterson regarding project permitting should include
all alternatives, along with analysis showing plans to avoid, minimize or compensate for
filling. The Arboretum Director should be included in that discussion.
ARTF should contribute to the alternatives analysis and sign off on content.
ARTF representatives should work closely with Strand Engineering in writing
specifications for implementing features described herein to ensure that they are consistent with
Arboretum goals, objectives, values, and principles.
All concerned need to know how many credits the Arboretum has agreed to provide the
City in total and how many stormwater-treatment credits would be derived from each alternative
at Manitou Way. This knowledge would improve the overall process and assist in future
planning that has been scheduled for Arboretum lands. It is specifically essential that the
Arboretum know how stormwater treatment credits obtained (or not obtained) at Manitou Way
would affect the stormwater credits that would be provide in Curtis Prairie.
13