Designing Riparian Buffers for North Field

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Designing Riparian Buffers for Northfield - Guidelines and

Suggestions for the Northfield Comprehensive Plan Revision

Contents:

Summary

Context

Riparian buffer proposal

Specific guidelines for Spring Brook (Rice) CreekReferences Cited and other references

Summary of protection resources available to landowners and municipalities

Maps showing buffers in the Spring Brook Creek/Heath Creek corridor

Prepared by: Oona Rokyta, Eric Shoemaker, Jacob Limmer, Greg Rafert, Lauren Miller, Arijit

Guha, Noah Brenner, all Carleton students

Assisted by: Mary Savina, Professor of Geology, Chris Robbins, Northfield citizen, Lisa Lukis,

Cannon River Watershed PartnershipNovember 16, 2000


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Context

Northfield is currently revising its comprehensive plan, anticipating the changing needs of the City

over the next 20 years. The planning process leading to the revision is an opportunity to recognizeand protect the natural resources within the City limits and in the directions that the City is likely to

grow. One of these natural resources is the waterways, including the Cannon River and its

tributaries.

Water quality in the Cannon River watershed - and throughout the Upper Mississippi River basin -

affects habitat both locally and globally. High nutrient levels throughout streams in the UpperMississippi are now known to contribute to hypoxia in the Gulf of Mexico (Downing et al., 1999).

The water quality in the Upper Mississippi is controlled by the water quality in the major tributaries

such as the Cannon River. Water quality on the Cannon River, in turn, is controlled largely by the

water quality in its tributaries, streams like Heath Creek, Prairie Creek, Wolf Creek, Spring Creekand Spring Brook (or Rice) Creek that flow through or near Northfield. Although these streams are

all unique, one of them, Spring Brook (Rice) Creek is a coldwater stream that supports a native

population of brook trout.

The major tributaries of the Cannon River that drain the area west of the Cannon may have initially

been subglacial conduits draining the Des Moines Lobe glacier (Patterson and Hobbs, 1995). The

valley landforms of Heath Creek and Wolf Creek - wide floodplains bordered by short steep slopes

- formed during this period of high discharge from the melting glacier. The area between these two

valleys now drains into Spring Brook Creek. These valleys have wide floodplains bordered by

relatively steep slopes, features largely inherited from the glacial past.

There is an abundance of scientific and technical literature documenting the ways that riparian

buffers protect streams, fish and animal habitat. Regions such as the Chesapeake Bay drainagebasin have been particularly advanced in designing buffers appropriate for urban and agricultural

land. In the rest of this document, we try to define guidelines based on some of these studies to help

the City of Northfield determine appropriate locations and widths for riparian buffers along its

streams.


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Riparian Buffer Zone Proposal

We use the term "riparian buffer" to mean a vegetated zone of variable width near the stream

channel, managed to reduce the impact of adjacent development on the stream, its banks and itsfloodplain and to preserve stream integrity. Among other benefits (Palone and Todd, 1998 and

other references listed below), riparian buffers help to prevent erosion, preserve channel integrity,

protect water quality by filtering agricultural and urban run-off and sediment (e.g. Komar andMagner, 1996), provide effective passive flood control and provide habitat for wildlife. Some

workers consider a buffer network a "stream right-of-way," a useful approach to planning

(Schueler, 1995b).

For maximum effectiveness, buffers should be planted in trees and dense grass with deep roots.

The US Department of Agriculture has developed a three-zone buffer model with forest closest to

the stream (zones 1 and 2) and dense grass filter strips furthest from the stream (zone 3) (Paloneand Todd, 1998). Buffers should be continuous along the stream; breaks in buffers allow runoff

and sediment to cross into the stream corridor (Schueler, 1995b; Weller et al., 1998).

Riparian buffers are compatible with a variety of passive recreational uses, including hiking,birdwatching, and fishing. In some instances buffers may be wide enough to accommodate paved

trails. Riparian buffers along creeks in Northfield should probably be publicly owned but may beused in part as park dedication during development.

Note: When establishing buffer zones, it is important to keep in mind the variability of guidelinesdepending on the specific geography of the area. Zones should be determined not by a pre-set

standard distance from the waters edge, but by physically pertinent aspects of the area: natural

boundaries of sensitive areas such as flood plains, sloping areas, wetlands and established habitats.

Criteria for buffer establishment in the Northfield urban area:

~Criterion 1: Identify the floodplain and include all of it in the riparian buffer zone.

The entire floodplain must be included in the buffer zone because it is one of the most vulnerable

areas around the stream, and the floodplain and stream interact closely with one another. A

floodplain must have some cover protection and must be an unpolluted area or it will erode andpollute the stream when it is flooded. Many communities require the buffer zone to include all of

the 100-year floodplain; a minimum base width of at least 100 feet is recommended (Schueler,

1995a; Smith and Hellmund, 1993).~Criterion 2: Incorporate current woodland areas in the buffer zone as much as possible (and

consider planting buffers into trees).

Forests make the best buffer zones for a variety of reasons (see attached tables from Schueler,

1995b and Agroforestry Notes AF-4, 1997, cited in Tjaden and Weber, FS733):~They are probably the most effective groundcover for preventing bank erosion, blocking wind and

intercepting rainfall, and holding dirt and sediment.

~Trees, as well as other vegetation, play an important role in nutrient uptake, not only from waterentering the stream from the side, but water coming from upstream.

~Shade helps to keep the water cool and decreases temperature fluctuation. This function is

particularly important for preservation of species that require cold water.


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~Deep roots stabilize the stream bank. Root systems also slow water flow and keep the soil porous,

so water moves more slowly and is better absorbed. This reduces flooding and allows the water to

be slowly filtered before it hits the stream, as well as letting some into the groundwater.

~Fallen branches slow water and provide good habitats for fish and invertebrates. It is essential tothe stream ecosystem functions of the riparian buffer that this "large woody debris" remain in the

stream channel.

~Trees are a pleasant environment for both wildlife and humans; they provide good habitat for avariety of animals and corridors for animal migration and human trail systems.

~Criterion 3: Protect steep slopes above the floodplain in the buffer zone and include some

distance of higher, flatter ground in buffer.

Steep slopes are especially vulnerable to erosion, as are the areas immediately above steep slopes.

This criterion also has direct benefits for farmers as it helps prevent valuable topsoil from washing

away, but is also necessary to protect streams in developed areas from excess sediment. All

undevelopable steep slopes should definitely be included, as these are extremely prone to soil losswhen not protected by groundcover. Schueler (1995a, 1995b) recommends including "all

undevelopable steep slopes (>25%) and steep slopes (5% to 25% slope at four additional feet of

slope per one percent increment of slope about 5%)" (Schueler, 1995b, p. 3). Note that the present

Northfield comprehensive plan identifies undevelopable steep slopes as those over 18%.Protecting part of the higher, flatter ground above the steep slopes in the buffer helps to slow

runoff and prevent it from concentrating as it crosses the buffer.~Criterion 4: Include stream tributary drainages, swales, and springs in the buffer zone.

Protecting headwaters and other water sources will offer the best water quality protection for the

water system as a whole (Smith and Hellmund, 1993). In addition, any areas where waterwaysconnect with one another are critical areas for wildlife.

~Criterion 5: Incorporate riparian wetlands in the buffer zone.

Wetlands are areas flooded or saturated with water, having hydric soils and supporting or able to

support aquatic vegetation. Wetlands are also tend to be excellent filters, their vegetationabsorbing high quantities of sediment, minerals and nutrients.

~Criterion 6: No storm water should be channeled through buffer zones or directly into thestreams.

Buffer zones can only do so much. Usually, a buffer can only treat run-off from less than 10% of a

streams contributing watershed because the other 90% of the water becomes concentrated into the

storm water system (Schueler, 1995b). Water quality can be greatly affected (both by toxicchemicals and excessive nutrients) if storm water from developed areas is allowed to flow directly

into the streams. Water quality in Heath Creek and other non-trout creeks should be at least

maintained, if not improved.~Criterion 7: Educate landowners, developers, and everyone else through zoning ordinances

and other means

Develop additional criteria to reduce the effects of concentrated and other drainage from

developments through the buffer: avoid storm sewers, seek infiltration areas or other alternatives,limit impervious surfaces to


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"wetland" on the comp plan map and legend. The "environmentally sensitive overlay" area should

extend well beyond the margins of the riparian buffer (as it does in the most recent comp plan

drafts).

Specific Recommendations for the Spring Brook/Rice Creek Watershed

Having discussed some of the methods and rationale behind riparian buffer zone construction, wewould now like to turn to some specific recommendations about the possible implementation of

riparian buffer zones on the Spring Brook/Rice Creek watershed. Given the strong possibility that

this watershed will be developed in the coming years, and the sensitivity of the cold-waterecosystem, we feel that it is incumbent upon the city of Northfield and other involved parties to

begin to design the riparian buffer zones on this watershed (Spring Brook Committee Report,

1999). Thinking ahead on this issue may help to ensure proper planning of buffer zones that both

meet the needs of preserving fragile ecosystems while at the same time allowing for limiteddevelopment. Our recommendations for this watershed are as follows:

1) Riparian buffer zones in this watershed should be inclusive of the entire floodplain, the steep

slopes adjacent to the floodplain (back to the ridgeline) and some distance beyond this point.No permanent structure development should take place within the floodplain limits.

2) The construction of buffer zones in this watershed should also include substantial streamside re-vegetation. This helps to cool the water, preserving the ecosystem for native brook trout, and

mitigating for some of the negative warming effects that are usually associated with

development.3) The stream channel itself should not be affected in any way by development. This includes the

construction of ponds, channelization, and the building of culverts.

4) Special attention should be paid to the fact the valuable coldwater ecosystem that exists in this

watershed is dependent on extensive spring inflow in the lower section of the creek. Anydevelopment that takes place in this watershed should be mindful of this fact. Efforts should be

made to limit the construction of impermeable surfaces or anything else that may adverselyaffect the functioning of these springs.

References Cited:

Downing, John A. and five others, task force members, 1999, Hypoxia in the Gulf of Mexico: Land

and Sea Interactions: Council for Agricultural Science and Technology, 44 p. Available at:

http://www.cast-science.org/pdf/hypo.pdf

Komor, S. C., Magner, J. A., 1996, Nitrate in groundwater and water sources used by riparian trees

in an agricultural watershed: A chemical and isotopic investigation in southern Minnesota: Water

Resources Research, v. 32, p. 1039-1050.

Palone, Roxane and Albert Todd, eds., 1998, Chesapeake Bay Riparian Handbook: A Guide for

Establishing and Maintaining Riparian Buffers: USDA Forest Service, NRCS, and CooperativeState Research, Extension and Education, NA-TP-02-97, 481 p. (The handbook is downloadable

as a .pdf file from http://www.fs.fed.us/na/morgantown/frm/water/riphbk/riphbkdl.htm)

Patterson, Carrie J. and Howard C. Hobbs, 1995, Surficial Geology, Rice County Geological Atlas:

Minnesota Geological Survey, County Atlas Series, Atlas C-9, Part A, plate 3.
http://www.cast-science.org/pdf/hypo.pdfhttp://www.cast-science.org/pdf/hypo.pdf


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Summary of protection resources available to landowners and municipalities

As humans develop more and more land for agricultural, industrial, and residential areas, the needto buffer our waterways has become evident. Many organizations, both public and private, and on

both regional and national levels have created grants and other financing programs to assist

communities and private landowners with the costs of buffering projects. The organizations withthe most available money are, for the most part, governmental offices. The Environmental

Protection Agency, the US Department of Agriculture, the National Fish and Wildlife Service, and

the Minnesota Department of Natural Resources all have large amounts of funding available tocover such costs as land acquisition, environmental consulting, and the implementation of a

buffer. Private organizations, such as the Nature Conservancy, also have money available. These

grants normally cover 25-100% of the total cost of the program. While there is a certain amount

of competition for the most lucrative grants, there are many grants that go unclaimed each yearbecause no one applies for them. A number of groups have studied the economic benefits of

buffers as well as the ecological benefits and found them to actually be profitable for the

landowner in many cases. For more information on this aspect of buffers please see

http://www.ctic.purdue.edu/Core4/Core4Main.html for a comprehensive cost analysis of severaltypes of buffers. While buffer projects can be very expensive, cost should not be viewed as a

hindrance to the implementation of a buffer plan because there are many funding optionsavailable to help defray the cost of protecting our waterways.

Designing Riparian Buffers for North Field

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