1:1 Purpose

The purpose of these guidelines is to assist petitioners, reviewers, decision makers, and the general public in understanding how natural features may be identified, evaluated, protected, and mitigated on sites being reviewed under the provisions of Chapters 55 (Zoning), 57 (Subdivision and Land Use Control) and 60 (Wetlands Preservation) of the Ann Arbor City Code.


1:2 Maps and Information Resources

Information about natural features in the City of Ann Arbor is available from the following public sources:

(1) City Planning Department. In addition to maintaining the City's official wetland inventory map, the Planning Department has a woodland inventory compiled in 1993 and a listing of species recognized as invasive in the Ann Arbor area. The department also has current and historical aerial photographs at various scales.

(2) City Parks Department. The Parks Department has a listing of recommended native species for the Ann Arbor area, a number of species surveys and information about endangered species. In addition, the Department has prepared stewardship and management plans for City parks. The City Forester has much information about public and private trees throughout the City.

(3) Washtenaw County Metropolitan Planning Commission. The County Planning Commission has prepared digital maps of significant natural features throughout the County, including wetlands, hydric soils, erodible soils, steep slopes, watersheds and woodlands. Maps are available in a wide variety of formats and scales.

(4) Washtenaw County Tax Equalization Department. The County Equalization Office maintains township parcel maps and aerial photographs.

(5) The University of Michigan. The University library system has early plat maps of the City in addition to copies of original land survey records, which often indicate the type of vegetation, terrain and conditions that existed prior to settlement. Some departments have copies of aerial photos of flights over the City. Some faculty have done extensive studies of many of the City's natural areas, and may otherwise be helpful with many aspects related to identification, assessment and management of natural features.

(6) The State of Michigan's MIRIS program (at MDNR) has aerial photos, maps and digitized information in many categories available for the Ann Arbor region.


1:3 State and Federal Statutes and Regulation

State and Federal governments have laws and regulations governing development in wetlands, in floodplains, in watercourses, on bottomlands, and in the vicinity of rare, threatened or endangered species of plants or animals. These statutes often require permits for development in or affecting these natural features. Permits as required from these agencies should be applied for concurrently with any request for area and site plan approval from the City. Contact the Michigan Department of Environmental Quality for its applications and review procedures.


1:4 City Review Process

When natural features exist on a site proposed to be developed, the petition will be subject to the following City review process:

(1) Natural Features Determination. The petitioner contemplating a project requiring City review is responsible for determining whether natural features exist on the site. This determination can be made by outside consultants retained by the petitioner. City staff will confirm these determinations during the review process.

(2) Preparation of Required Plans. The Land Development Regulations specify what information must be shown on plans submitted for City review. Prior to submitting a plan required by Chapter 57, the petitioner should meet with City staff to review the proposed site layout and consider suggestions for complying with City requirements. In addition, petitioners may wish to consult with experts on questions regarding the type, extent, quality, and management needs of natural features, and on the impacts of various design approaches on these features.

(3) Plan Submission. When at least one natural feature is determined to exist on a site a natural features statement of impact must be provided. The statement will contain the following information:

A site inventory map. This map must clearly show the locations and types of all existing natural features on the site and extending 50 feet beyond the property lines. The drawing should delineate edges of woodlands and wetlands, show buffer areas, show watercourse streambanks, pond ordinary high water marks, floodways, and floodplains. Landmark trees on the site should be located by numbered dots, with an accompanying database table of corresponding species and size listings.

A natural features protection plan. This plan must delineate natural features to be retained on the site or excluded from development. Lines should show the limits of soil disturbance expected on the site. Protective measures such as barrier fencing, restrictions on traffic and storage of materials under trees, soil erosion control measures, etc. are also to be shown on site plan submissions. In some cases, this plan may include information on how the retained natural features are to be sustained on the site.

An alternative analysis. A report will be made which displays and discusses the alternative approaches and designs that were considered in arriving at the design proposed, in an effort to minimize disturbance to natural features on the site. A written justification will be made as to why the design proposed must cause the degree of disturbance to natural features planned, and explaining how the mitigation proposed is a wise course of action.

A mitigation plan. The mitigation plan will show how natural features that will be disturbed or taken are proposed to be mitigated.

(4) City Staff Review/Analysis of Alternative Designs. Planning Department staff will coordinate the proposal's review by various City departments. Staff will work with the petitioner to resolve departmental comments. In addition, City staff will evaluate the alternative analysis to determine if the proposal represents the least disruptive option. Once the petitioner has responded to departmental comments, staff will develop a written report for the City Planning Commission, which will include recommended action in motion form. If a development agreement is negotiated, a copy of it will be attached to the report submitted for the review of the Commission.

(5) Planning Commission and/or City Council Review. Once information and plans submitted to the City are complete, the formal public review process begins with the City Planning Commission. Exact procedures for reviews before the City Planning Commission and the City Council are written in other documents, available in the Planning Department. A public hearing will be held at Planning Commission and, if applicable, at City Council before a decision is made on the proposal. In determining whether the proposal complies with the approval standards described in Chapter 57, the approving body will rely (in part) on these Guidelines for Protection and Mitigation of Natural Features. (Please note: These Guidelines are highly simplified views of the nature of natural features in Ann Arbor. They are intended to be helpful to investigation, design and evaluation processes associated with development of land in the City. They are not formal rules, and they only begin to bring understanding about what is important about natural features in Ann Arbor.)

(6) Permits. Permits may be applied for at the Building Department after the petitioner has received notice, in writing, of official City approval of plans. Generally the first permit issued will be a grading permit. All natural feature protection measures specified in the approved plans must installed and maintained on the site throughout construction. Inspections are conducted to see whether sedimentation and erosion controls and protective barrier fencing are in place and are being maintained, whether limits of construction and barrier fencing are being observed, including around trees, whether pavements and streets are clean of soils, whether debris is properly contained on the site, whether site work is proceeding according to plan.


1:5 Natural Feature Protection and Mitigation Guidelines

The following sections discuss each natural feature in substantial detail. Each feature is discussed with respect to:


(1) Endangered Species Habitats

Endangered species are most likely to be found in the midst of natural areas described in these guidelines as "highest concern." When a rare, threatened or endangered species is found, careful assessment should be made of the species and the area in which it is found. These organisms and their habitat may be intolerant of change caused by a development, such as change in hydrological conditions, even if the habitat itself is outside the limits of soil disturbance for a project. These species and their habitats are important to the City for the richness and diversity of species they offer.

(A) Identification.

Within Ann Arbor, the areas most likely to contain endangered species are sandy, wet bottom lands and wetlands along the Huron River, along its tributaries, and in the many small pocket wetlands in native forest fragments. Many of these areas can be quite small in size. Rare and unusual endangered species (of ferns, bryophytes, orchids, grasses, etc.) may also be found on disturbed ground -- including along shorelines and streambanks, flooded areas, old farmed fields, borrow pits, eroding slopes, burned areas, embankments along railroads and roads, in cemeteries, old settlement areas and farmsteads, etc.

(B) Protection Priorities.

The protection of endangered species and their habitats are regulated by the State of Michigan (MDNR), in cooperation with the US Fish and Wildlife Service. The City will work in coordination with state and federal regulating agencies to identify the best protection approach, based on the specific characteristics of the species involved. In general, these species and their habitats should be excluded from development and protected from the impact of development.

(C) Mitigation.

The precise mitigation requirements for an endangered species habitat which must be damaged or destroyed for development will be determined in cooperation with state and federal officials. A permit is required from these agencies.

(D) Protection Measures.

The City will work in coordination with state and federal regulating agencies to identify appropriate protection measures to sustain the species, based on the specific characteristics and needs of the habitat and species involved.

(2) Floodplains (100-Year)

Floodplains serve to minimize damage to land and water resources because of their capacity to store water. In so doing they control erosion, silting and contamination of water features and aquatic wildlife. Prior to settlement of the City (1824), floodplains were forested or were wet meadows of several types, and existed in many more locations than now. Healthy, stable plant life is important in determining a floodplain's capacity and function in slowing, filtering, and cooling water moving through them. Floodplains are not a desirable location for storm water detention facilities.

Floodplains also may qualify as wetland or watercourse natural features. With watercourses and other surrounding natural features, floodplains serve as vital wildlife reserves and linking corridors for important populations of plants, animals, aquatic organisms, and natural associations throughout the City.

(A) Identification.

Floodplains, floodways and watercourses that have watersheds two square miles or larger are officially mapped and regulated under provisions of Federal and State statutes. Floodplain and floodway boundaries are available on Flood Insurance Rate Maps (FIRM), produced by the Federal Emergency Management Agency (FEMA). The City may ask for investigation and mapping of flooding zones along watercourses on sites not officially mapped. If substantial flooding potential exists, and buildings and structures are proposed in the floodplain, the City may ask for formal hydrological studies to determine the long term safety and the hydrological and environmental soundness of a proposed project.

(B) Protection Priorities.

Highest concern: Floodplains with natural plant life and natural landform conditions are very important to protect from development. They involve native floodplain forest fragments (extremely rare), or native sedge or fen meadows (rare and important natural areas, likely habitats for rare species in the City). These areas not only are rich biologically, but provide floodplain function.

The City's original floodplain forests were populated by red ash, black and silver maple, and hickories. In disturbed conditions these forests include sycamore, elm, cottonwood and native willows. Such forest fragments still exist in some areas along the Huron River.

Floodplains of highest concern should be preserved as part of any development proposal (which means not only is there no disturbance to soils, but there is no disturbance to surface and subsurface hydrological regimes). In cases where these habitats exist and are being invaded by exotics, every reasonable effort should be taken to restore the habitat as part of a development proposal. Where enhancement of capacity and function can be done, it should be.

Midlevel concern: Forested floodplains dominated by exotics, including black alder, several willows, and floodplain meadows dominated by cattails or purple loosestrife.

While these floodplain forests are not as important to protect for their biological value, they are vital to the continued function/capacity of the floodplain. Whenever possible, these areas should be left undisturbed. In many cases, restoration of these areas with native plants could be useful in enhancing the function, appearance, and wildlife value of the floodplain.

Floodplains of midlevel concern should not be built upon. In any case, the floodplain's function and capacity should not be diminished. Where enhancement of capacity and function can be done, it should be.

Lowlevel concern: Floodplains characterized by paving or turf or otherwise cleared land are not as important to protect from development, if some must occur. A key concern to guide such decisions should be whether there are flooding and water quality problems in the watershed, and what opportunity exists for mitigation to address these problems.

(C) Mitigation.

Where the actual volume/land area of a floodplain is affected by a proposed development, the volume/land area of the flood plain lost should be restored elsewhere on the site or in the watershed.

Where paved surfaces are proposed in a floodplain, they should be minimized to the fullest extent possible. The area of paved surface on a site in a floodplain should be mitigated by new floodplain with native floodplain species installed elsewhere on the site or elsewhere in the watershed, or it should be mitigated by a landscape design for the site that enhances floodplain function.

Where forest fragments, fen and sedge meadows are removed or disturbed, they should be mitigated to replicate equally valuable natural features on the site or in some other location in the watershed.

Lesser quality plant communities should also be replaced, but the level of diversity of the mitigation may be less (using native associations is more desirable).

To the fullest extent possible, regardless of existing conditions, landscape design for a project proposed in a floodplain should avoid turf and use (preferably native) associations of plant materials that can become effective on the site as healthy floodplain plant communities.

Alternate mitigation (when these procedures are not possible) could include natural areas management or restoration work on floodplains elsewhere on the site or within the watershed. They might include addition of storm water control facilities beyond other code requirements.

(D) Protection Measures.

Tolerance for soil erosion on any construction site in any floodplain should be very narrow. Special, effective soil erosion and flood protection techniques should be devised and required in each instance, during construction and for as long afterward as it takes for vegetation to become very well established and for soils to be stable during storm/flooding events. These techniques and devices need careful design and maintenance to protect against washout in storm events and damage to water resources.

(3) Woodlands

The City's woodlands are of two primary types, either planted and volunteer, or naturally regenerating native forest. Nearly all of the City's land area was covered by mature native forest associations, in 1824. Nearly all of those forests were cut down in the 20 years between 1840 and 1860. A substantial majority of the land area of the City was then cleared of stumps and all herbaceous vegetation for European style farming. As the City has urbanized, farmed land has been developed and planted with a wide variety of ornamentals, often so densely as to qualify as woodlands. Where farmlands have been abandoned but not yet developed, volunteer species of trees and invasives rapidly colonize, often so densely as to qualify as woodlands. Some native species managed to regenerate in these areas, but often seed stocks and microflora in the soil necessary for direct regeneration of forests as they existed in 1824 were destroyed by the farming and urbanization processes.

A patchwork quilt of areas once forested across the City were never cleared and farmed, even though all the trees were cut down. These sites were the "back 40's" of farms people chose not to actively crop, were areas wet and difficult to drain, or were areas on steep slopes. Many of these sites have been completely destroyed as the City has been built, many have already had housing built in them, some are in parks, some remain undeveloped. These lands have regenerated trees and sometimes a forest association similar to what existed in 1824.

These native forest fragments and old trees are important to the scenic and biological quality of life the City. These areas can simply be a grove of native trees much older than the houses and gardens under them. Or they can be regenerating ecosystems (trees in the canopy, dogwoods, shadblow and witch hazel in the understory, very few shrubs, and a diverse herbaceous flora).

(A) Identification.

Native forest fragments are visible on early low altitude aerial photographs of the City, before the invasion of exotic woody plants. These fragments are typified by their unfarmed soils and by the combination of plants constituting an ecosystem association recognizable as dating back to 1824. These fragments can be floodplain forests (Black and Silver maples, Red ash, hickories), wooded mesic or wetland forests (red oak and red maple), dry forests on the tops of sand and gravel filled moraines and kames (White oak, Hickories and White ash), to mesic forests on moister upland soils (Sugar maple, Red maple and American beech). A very wide variety of species existed as part of these associations, and can be present in the regenerating fragments. Sometimes only the trees remain, such as the grove of old Burr oaks in the vicinity of St. Andrew's Church B the only remaining trees of the Burr oak savanna called Ann's Arbor.

Urban woodlands are areas which have the density necessary to meet the definition of woodland used by the City, but which are not native forest fragments. Groves of planted trees, often of pines or spruces are found throughout the City. Volunteer trees may come into an area so densely as to create a woodland under the definition. Some people may plant and cultivate trees densely enough to qualify. These landscapes do not function as self-sustaining ecosystems, but they can function as valuable wildlife habitat, can provide great scenic resource, do influence the climate, and make life in the City more enjoyable for people.

Pioneer woodlands are those which arise on disturbed soils, such as soils which have gone through a period of cultivation in the European monocultural style, or soils which have been overturned, moved, or graded to the extent that seed (and the related, beneficial soil microflora) for regenerating the ecosystem is destroyed or greatly diminished. Pioneer woodlands are usually found on abandoned farm fields or waste sites of various sorts. These woodlands are often dominated by invasive exotic shrubs and are impoverished wildlife sites.

In some cases, native forest fragments are colonizing into fields once farmed adjacent to them. These areas are rich wildlife habitats and should be treated with care, along with the native forest fragments.

(B) Protection Priorities.

Highest concern: Native forest fragments, particularly those that still have a wide diversity of native species at all levels (woody and herbaceous plants) are the most important sites to protect from development and from the impact of development. Many of these sites have been and are being rapidly invaded by exotic species (of shrubs, primarily), and need active care as well as protection to sustain them.

The highest quality among these fragments should not be built upon. These fragments should be retained as public land and managed as natural areas. Effort should be made to preserve and protect all remaining native forest fragments to the fullest extent possible. Further fragmentation is not desirable.

Midlevel concern: Ann Arbor's urban woodlands are directly derived from people's planting activities, as the City developed. Woods and trees involved in these settings very likely have considerable importance to people who live near them.

Lowlevel concern; Generally speaking, pioneer woodlands that are now developing in the City are often dominated by exotic trees and shrubs, with an occasional large native tree that a farmer retained in his field. New, well designed and well planted built landscapes would be more appealing and more valuable in the long term, than protecting these woodlands. Vegetation must be removed in order to return it to a more natural and pleasing landform. Landmark trees and other valuable features may exist on the site, If so, they would be key concerns in the design of development for these areas. (Caution: rare endangered species can also exist on disturbed sites.)

(C) Mitigation.

When native forest fragments must be taken in whole or in part, they should be mitigated by the installation of replacement trees or by the creation of an area planted with a comparable plant association (trees, understory trees, shrubs, herbaceous plants B not including exotics) on the site or elsewhere in the City.

Where a valuable native forest fragment must be partly destroyed by development, the balance of the fragment should be actively managed as a natural area, to sustain it into the future. This includes the important task of controlling invasive exotics.

Urban woodlands may also have considerable value to City residents. Development in them should be handled as sensitively as possible. Tree replacements for trees taken from such a woodland should be replaced on the site in a manner that compliments the character of woodland. Landscape design of the site should also complement the character of the woodland, and should be sensitive to screening and otherwise providing affected neighbors with pleasant views into the site.

Care should be taken during the development process to conserve topsoils which must be disturbed on site, and to install plant materials into optimum conditions. Compacted soils placed by heavy machines are not suitable for successful establishment of many types of plants. Retained top soils can be used in new planting zones to great benefit.

Alternative mitigation plans which could be negotiated could include management or restoration of comparable natural features on the site or on public lands elsewhere in the City, or donation of trees to the City to be planted on public land, donation of time and materials to assist the City in managing valuable natural areas on public land. Valuable wetlands on the site or elsewhere could be enhanced, storm water retention capacity could be increased, floodplain capacity and function could be improved B each beyond that already required by code.

(D) Protection Measures.

Native forest fragments excluded from development should be defended from all intrusions during development by well maintained barrier fencing.

Where native forest fragments are to be built in, but not completely removed, then those areas to be excluded from development should be clearly fenced during the process. Grading, roads, walkways, utility lines, and all other aspects of soil disturbance should be minimized to the fullest extent that sound design and public safety will allow.

Clearing for buildings should be strictly minimized to the least area needed to work around buildings. Excavated spoils from basements and other needed grading should not be spread on the site in the native forest fragment area. Very careful handling of trees near the building envelope should be undertaken to the fullest extent possible.

Where management of retained native forest fragments is undertaken, these activities should be conducted according to the principles and techniques described in a well developed management plan. Advice from qualified natural area managers should be sought and included in such plans. A key element of these plans should be the control of invasive species, which threaten natural areas throughout the City.

Wherever trees are to be retained in any type of woodland in the City, protection measures in accordance with the Natural Features Protection section of Chapter 57 of the Ann Arbor Code of Ordinances must be adhered to.

The most effective way to save trees is by planning ahead for their protection. Four steps will help accomplish this:

1. Delineate areas with severe limitations and stay away from them (provide barriers).

2. Design the site to minimize grading/soil disturbance in the vicinity of retained trees.

3. Provide for adequate and effective stormwater management.

4. Design landscape installations to complement and honor retained trees.

In addition to protective fencing at the Critical Root Zone, a number of other construction techniques can help save trees. These include placing utilities under pavement instead of under trees; tunneling utilities under trees instead of trenching; using granular material when placing minimum amounts of fill over roots; excavating by hand; and keeping heavy equipment and vehicle traffic away from the Critical Root Zone. Grading changes should not either increase or decrease moisture conditions in the Critical Root Zone.

(4) Landmark Trees

Large, old, picturesque, rare, well-located, or otherwise special and interesting trees play an important role in the character of individual properties, and in the fabric of the City as a whole. All the trees in the City together have positive effects on the climate of the City, on its ability to attract and sustain wildlife, and on its visual beauty.

(A) Identification.

Trees which qualify as natural features are, generally speaking, any tree larger than 24 inches in diameter at breast height and any tree of a size listed on the Landmark Tree List (in the Land Development Regulations).

Large trees in natural areas (native forest fragments or forested wetlands or floodplain forest fragments) will often qualify as Landmark Trees.

(B) Protection Priorities.

Highest concern: Landmark Trees of most importance to protect are ones which are rare, unusual, old or historically significant. Certain trees may play a special role in the visual resources of a site or an area. If the trees are native to Ann Arbor (known to have grown here in 1824), they are particularly important to protect. Such trees should be retained and be used as a valuable and integral part of the new development's landscape.

Midlevel concern: Trees which are mature, late succession species, provide wildlife habitat or visual screening, represent good diversity of species, have interesting flowers or other features, or are in proximity to a native forest fragment and are related to it.

Lowlevel concern: Pioneer species of woody plants arising on sites with highly disturbed soils, trees and shrubs not native to the region and known to be invasive (seeding prolifically and naturalizing into the neighborhood or into natural areas). Generally speaking, a fine quality planted landscape can be more valuable in the long term, and more appealing to more people in the short term than many pioneer woodlands in the City.

(C) Mitigation.

Required or desired replacement should include the most appropriate, non-invasive species as part of the project design. Replacement requirements include using species native to Michigan, and a diversity of species in a range of sizes. Where trees are taken from a natural area, it is the natural area which should be replaced or restored at some other location C involving much more than just tree planting. Trees which go into such a project may need to be smaller in size to find enough of the species needed to make a viable start to creating an ecosystem.

Replacement trees need a chance to become as great as the trees they replace. Genuine concern for soils and cultural needs of new plants should be a part of the design process. Many species of trees will never thrive in compacted, fill soils C or in conditions not suitable for their optimum growth. Recognition of these realities is critical to successful replacement.

Where it is not possible to install the number of trees required, alternate mitigation plans may be developed B including active management or restoration of natural areas on the site, planting of trees on public land elsewhere in the City, additional storm water controls beyond that required in code and of help with flooding conditions on the site or in the watershed, donation of public land on the site or elsewhere, etc.

(D) Protection Measures.

Tree roots are very vulnerable to disturbance. Trees generally do not have tap roots, nor a structure like what is above ground. They have a flat mat of roots extending within several inches to several feet from the surface of the ground and out a distance at least the diameter of the drip line of the tree. The most important roots are the fibrous ones, on the outermost ends of the root branches.

All construction activity (including the affects on soil moisture and drainage of grading changes in the area) should be excluded from the Critical Root Zone (CRZ) of trees to be preserved according to submitted plans. The expected survival rate for trees treated in this manner is very high.

These activities damage or destroy tree roots and threaten the life of trees: Soil compaction from vehicle and machine parking and traffic, excavation or filling, storage of materials, grading changes that affect soil moisture in the root zone at any time, and insensitive landscape design and installation techniques (including irrigation).

The most effective way to save trees is by planning ahead for their protection. Tree areas with severe space and other limitations can be avoided, grading can be minimized or eliminated in tree areas, effective stormwater management facilities can be installed in a way to keep moisture levels in tree areas unchanged, and the design and installation of landscape elements (including irrigation) can be done in a way which honors the needs of protected landmark trees. Oaks, hickories, maples, beeches C many of the native hardwood trees and most old trees - do not adapt to changes caused by construction activity in the CRZ.

In addition to protective fencing at the Critical Root Zone, a number of other construction techniques can help save trees. These include placing utilities under pavement instead of under trees; tunneling utilities under trees instead of trenching; using granular material when placing modest amounts of soil over roots; excavating by hand; and keeping equipment and vehicles away from the Critical Root Zone.

The Limits of Soil Disturbance notations shown on plans around protected trees should be marked on the site with barrier fencing, throughout construction.

(5) Steep Slopes

Steep slopes in Ann Arbor are found on the sides of moraines, kames, and ravines. The City's landforms were laid down by the melting glaciers of 10,000 years ago, and then sculpted by the runoff of glacial meltwater in ancestral rivers and streams. Many of the City's current watercourses are in locations similar to those ancestral locations, and many of the scenically important slopes crafted in part by them are along watercourses. Scenic qualities and concerns are associated with slopes, because the change in elevation creates views of and from locations on the slopes. Because of the difficulty of farming and development, many of the City's natural areas exist on steep slopes.

Steep slopes are prone to erosion if the vegetation on them is disturbed, or if surface runoff is directed toward them. As a result, disturbed slopes often result in siltation of a watercourse or disturbance to land below.

The important bluffs concentrated generally south facing through the middle of the City are end moraines and kames, a result of a pause in the glacier's recession and the erosive effects of runoff. These features give Ann Arbor a particular character, one quite different than places which have little or no topography, quite different than places in or near mountains). The Huron River has played a key role throughout the time period since the glacier. Taken together, the Huron River and the landforms which embrace it, and the native forest fragments covering many of the steep slopes of those landforms are the preeminent natural features of our City.

(A) Identification.

Moraines and kames located adjacent to the Huron River are particularly obvious (they are end morraines, accentuated by the erosion done by the river over the last several thousand years). They rise fifty to one hundred feet above the river, and sometimes are steep inclines. These slopes also are often covered by native forest fragments, because they were too steep to clear and farm.

(B) Protection Priorities.

Highest concern: Slopes of 40 percent or greater, facing or adjoining the river should be protected as key scenic assets. Where these slopes are visible from locations people frequent off the site, development on them can have dramatic impact upon the City's visual character. Such impacts (from buildings above the canopy of trees, for example) should be carefully considered. And, because of the high probability of erosion, steep slopes should be left undisturbed.

Midlevel concern: Slopes between 20 - 40 percent not directly associated with those facing the river or adjoining them should be disturbed to the least extent possible. Special techniques must be designed and used to prevent soil erosion. Where these slopes are visible from locations people frequent off the site, development on them can have effects upon the City's visual character. In some cases, these impacts should be considered as part of the design and planning approval process.

Lowlevel concern: Slopes of lesser gradient and manmade slopes. They should be incorporated into the site design in such a way that they complement and blend well with both the needs of the development and the character of surrounding landforms and topography.

(C) Mitigation.

No particular mitigation of steep slopes that are built upon is required, other than no new drainage may be directed over the steep slope. However, where steep slopes also have trees or woodlands or watercourses or other natural features, or where erosion could be a threat to such features, requirements to protect these features should be incorporated into the design and construction processes.

In no event should grading for a development on a site with a steep slope create erosion problems for any neighboring property.

(D) Protection Measures.

The primary goal in protecting steep slopes is to prevent erosion and subsequent damage to natural features on and off the site. The use of retaining walls can reduce the amount of grading necessary, but are not encouraged (they are rarely durable structures). Underground utilities should not be located in steep slopes, and should not run lengthwise along them. Drainage should be directed to inlet structures and not be permitted to flow down slopes during and after construction.

Protection measures for other natural features placed at risk by intrusion onto a steep slope should be designed and implemented in such a way that risk of damage to the natural features involved is the minimum possible. These provisions may need to be significantly more strenuous than those which might be implemented for the same natural features on flat ground.

(6) Watercourses

The preeminent natural feature in the City is the Huron River, its tributaries, and the glacial landforms and topography which embrace them.

These watercourses bring water to and through a property and, together, create vital wildlife corridors through the City. They are key components of scenic beauty and of outdoor attraction for people in the City, and on many individual properties. They also serve the practical function of providing drinking water, either directly (the City's main water supply intakes are in Barton Pond) or indirectly by the primary conduits of ground water recharge.

The Huron River is the main watercourse through the City. Only small portions of its length remain naturally flowing, inside 1824 stream banks. Its configuration and flow patterns were changed with the building of the Edison electric utility dams. Because of these dams, the potential for flooding on the river through the City is limited. (Flooding is a problem on the tributaries.)

Other watercourses in the City are tributaries and subtributaries of the Huron River. Many parts of streams and some entire streams no longer exist above ground. They have been placed underground in storm pipes (e.g.. Allen Creek). Most of the remaining tributaries are in poor condition because they have been overwhelmed by the increased runoff generated by development of the City.

Construction of structures in watercourses and bottom lands of lakes and ponds is regulated by statutes in the State of Michigan, under permits usually issued by the Department of Environmental Quality. A permit will be required from these agencies. Their regulations aim to minimize dredging and filling in watercourses and in bottom lands, to minimize negative impacts which result from necessary activities of this sort, and (in the case of wetlands which are associated with these projects) replace the lost resources.

(A) Identification.

Many streams and bodies of water qualifying as watercourses and bottom lands will be visible on aerial photographs and maps, many small ponds and the uppermost reaches of some streams may not. These features are readily identifiable in the field.

Watercourses are clearly delineated on floodplain maps. In the upper reaches of watersheds too small for those maps to have been done, watercourses can and should be identified as the top of the bank of the channel carrying water or as the ordinary high water mark line of a pond.

Streams in the City may cross relatively steep terrain, and are likely to be combined with other valuable natural features, including valuable woodlands, wetlands and floodplains.

(B) Protection Priorities.

It is in the City's best interest to protect watercourses in as natural a condition as possible, and to control storm water in watersheds in such a way that watercourses are not damaged and eroded during storm events. While storm water is regulated by another Chapter, the design of many elements on each site directly determines the way water is handled and what impacts it will have both on and off the site.

Highest concern: Watercourses with natural areas around them (wetlands or native forest fragments), watercourses integrated into steep terrain, and watercourses still flowing in natural channels should be preserved as part of any development proposal. Crossing locations should be kept to the minimum necessary to provide access. Wide buffers should be provided to maintain a corridor of for wildlife along stream ways. Where streams in these conditions exist on a site, they are likely the most important design element of the site. The design should capitalize on the value of these features and sustain them.

Midlevel concern: Urbanized above-ground watercourses are ones that no longer have much of a natural character, but have not been placed into a storm drain beneath the ground. Whenever possible, development should restore these watercourses and associated natural features and take advantage of them as a design amenity. Effort to control erosion, sedimentation and contamination problems is strongly encouraged, as is the connection of natural corridors across properties.

Lowlevel concern: Where watercourses are already underground, flood plain capacity and function are the main concern. Restoration of the surface watercourse is encouraged, particularly if the effort can assist in storm water control.

(C) Mitigation.

Watercourses should be crossed at the location where there is the least physical, scenic and biological impact upon the watercourse and its surrounding natural features. If surrounding natural features must be disturbed to facilitate the crossing, they should be mitigated as prescribed in other sections of these Guidelines or by other code requirements.

(D) Protection Measures.

Tolerance for soil erosion on any construction site in or near any watercourse should be very narrow. Effective soil erosion control and flood protection techniques should be devised and implemented, during and after construction. These techniques and devices need careful consideration.

(7) Wetlands

The City's original wetlands were open meadows, predominantly fen/wet meadow ecosystems associated with watercourses tributary to the Huron River. There were also pocket wetlands, often only showing water in the Spring and during wet Summers, throughout the flat forested landscape.

Few original wetlands remain in Ann Arbor. The majority of them have been drained and destroyed, as a matter of past public policy. The quality of water in the Huron River after any storm event can clearly show how unwise these actions have been.

Some wetlands remain. They can exhibit characteristics of their original ecosystems (which can be seen by the presence of sedges and forbs if they are open meadows, or by woodland pond species if in native forest fragments), More likely, the wetlands which remain are highly disturbed and are dominated by only a few common species of plants (cattail or exotic loosestrife), or they have been overwhelmed by invasive exotics, including buckthorn and willows.

(A) Identification.

Wetlands are visible in low altitude aerial photos, particularly older ones prior to the invasion by exotic shrubs and trees. A map of potential wetland areas is on file in the City Planning Department. The boundaries of wetlands are further determined by considering vegetation and soils in the field.

(B) Protection Priorities.

Highest Concern: Large wetland complexes, forested wetlands and wetlands along watercourses, with native plant associations still intact or regenerating. These habitats should be carefully protected from development and from effects of development (no change in hydrology) In general, wetlands with important native ecosystems cannot tolerate use as retention basins for storm water runoff from developed areas. A separate filter and retention system should be developed, so that impacts upon the wetland are minimal.

Midlevel Concern: Disturbed wetlands with underlying hydric soils, such as on once farmed lands constitute genuine opportunity to restore some of the capacity and function and diversity of species removed from the City over the last 100 years Maintaining and enhancing the biological and hydrological value and function of these wetlands should be the primary concern. Use of these wetlands as retention basins can be acceptable, as long as there are separate filtration basins and as long as the volumes of water involved do not overwhelm the plant life which must be sustained in the wetland.

Lowlevel Concern: Low quality wetlands are those that have been greatly damaged, have been reduced to open water and/or a few species of plants, or are dominated by invasive species. Replacement or relocation of these wetlands is more acceptable, if they must be taken for development. In many cases, these wetlands can be effectively repaired and used for storm water retention and filtration.

(C) Mitigation.

The requirements for mitigation of wetlands removed as a part of development are provided in Chapter 60 (Wetlands). In order for a mitigation plan to be successful, the constructed wetland should be located in an area with hydric soils. The control of invasive exotics is an important part of the design and implementation of any wetland mitigation project.

(D) Protection Measures.

Where wetlands are to be used as a part of a storm water retention system, the Rules of the Washtenaw County Drain Commissioner (April 1996) should be followed to minimize negative impacts on the wetland. Chapter 60 provides requirements for protection of wetlands during construction.










1:1 When a development petition is submitted to the City Planning Department for review, staff will determine if the site meets one of the following criteria:





1:2 If Planning Department staff determines that the petition meets one of the criteria, a copy of the proposal will be sent to the University of Michigan Museum of Anthropology for review.

1:3 Museum of Anthropology staff will complete a file assessment to determine if there is a need for a field survey to document any archaeological finds and notify the Planning Department of its findings.

1:4 If a field survey is necessary, the Planning Department will notify the petitioner and supply a consultant listing and the specifications for a field survey.

1:5 The petitioner is responsible for making arrangements for the field survey to be completed and a report prepared. The petitioner must submit the report to Planning Department staff before final approval of the development petition will be scheduled. In the event that a field survey cannot be done due to frozen ground conditions, approval of a development petition will be made conditional upon completion of such a report.

1:6 If archaeological finds of significant impact are determined to exist on the site, the Planning Department will set up a meeting with Museum of Anthropology staff to review the report and determine whether modifications to the development plans are necessary.









1:1 As a requirement for approval of a plat or site plan, the Department of Parks and Recreation requires developers to pay a street tree escrow fee for the purpose of planting trees on the public street right-of-way abutting the new development.  This process is administered through the Forestry Division of the Parks Department and the current rate is $1.30 per linear foot of street frontage.  This requirement is not to be confused with the Chapter 62, Landscape Ordinance, which requires specific plantings on private property.

1:2 Consideration for Existing Trees.

In situations where there are existing street trees meeting City standards, the front foot base figure will be reduced by 45 feet for every existing acceptable tree.  This is the average space required for one tree.


1:3 Provisions for Request for Larger Trees.

Property owners and developers who prefer to provide larger trees have an option which is a front foot charge proportional to the size of tree requested.  For example, 3 - 3 1/2" diameter balled and burlapped (B & B) trees would require $4 foot to cover the cost.  This charge will be per foot depending on the size of the tree.  The basis formula for computing the front foot charge for any given tree size is as follows:


$1.30 x trunk diameter in inches = per front foot escrow charge.

The formula was determined by dividing the City's cost of planting a three-inch diameter tree ($175.50) by 45 feet spacing for each tree.  This figure of $3.90 per front foot was divided by the tree size (three inches) which equals $1.30 charge per inch of trunk diameter.  For example, the charge for large tree planting would be as follows:

- 2" B & B x $1.30/" = $2.60/' front x 45'/tree = $117/tree

- 2.5" B & B tree x $1.30/" = $3.25/' front x 45'/tree = $146.25/tree

- 3" B & B tree x $1.30/" =$3.90/' front x 45'/tree = $175.50/tree

This will vary from year to year to account for inflationary increases. 


1:4 Method and Timetable for Payment and Planting.

The escrow is to be paid by the owner or the individuals submitting the site plan or plat.  The escrow amount is to be deposited with the Parks Department.  The deposit for site plans must be made in full prior to issuance of a building permit.  In the case of a plat, the escrow payment will be charged according to the provisions of the subdivision agreement.


1:5 Developer Provided Street Trees.

Developer may choose to provide the required street trees.  In this case, the appropriate escrow amount shall be deposited prior to development, however, it will be refunded after the Forestry Division has approved the street tree plantings.  The Department's planting specifications are available on request.

Another option is the incorporation of private landscaping into a streetscape setting.  This may be done with introduced landscape materials or existing on-site plant material.  The general requirements of the Department are that quality planting materials be used.  Each plan of this type will be reviewed and judged on its individual characteristics by the City Forester.


1:6 Street Trees for Unique Sites.

There are a few right-of-way situations in the City where normal grass extensions do not exist, but the possibility of planting street trees should be considered.  The most common of these situations is the CBD (Central Business District) where the right-of-way is entirely made up of concrete or asphalt sidewalk.  Although not all these areas can be planted because of other restrictions, many are feasible street tree planting locations.  Each site will be examined and analyzed individually.  Since the number of trees that can be planted in these types of areas will vary greatly from site to site, the escrow charge will be based on a portion of the cost per tree that can be installed.  The developer will be charged for all excavation (concrete removal or planter box construction) costs and the cost of a tree guard which shall not exceed $300/tree.  The Forestry Division and the Dean Fund Committee will make arrangements to cover the cost of purchasing and planting a 3" - 3 1/2" B & B (minimum) tree.  The charge of the developer will be determined when the site plan or plat is approved.

Another unique situation would be where normal extension planting is totally restricted, however, it is feasible to plant outside the right-of-way.  In this case, the property owner would have to agree to such planting.  If all parties can agree on a plan, the normal escrow, or in the case of concrete sites, a per tree charge would be applied.









1:1 The petitioner shall secure and present to the Planning Department, as part of any area plan, site plan or plat submission, a written analysis of the impact of any automobile-related development proposal on the existing public street; vehicular, bicycle, or pedestrian traffic; and/or existing public street parking. Exceptions to this requirement will be site plans or plats that will generate less than three vehicle trips per unit per peak hour or 50 vehicle trips per peak hour. The generation of trips shall conform to the methods specified in the current edition of the Trip Generation Manual, a publication by the Institute of Transportation Engineers.

1:2 Such analysis shall include the following:

(1) Existing traffic volumes passing on all streets abutting the proposed development during the peak hour. Traffic from other new and proposed developments in the area should be considered.

(2) Existing peak hour turning movements of vehicular traffic at all public street intersections within 200 feet of the proposed development, or those intersections that may be impacted by the proposed development.

(3) Projected peak hour generation rate and peak hours of generation for the proposed development.

(4) Projected peak hour traffic movements as a result of the establishment of the proposed facility.

(5) A capacity analysis for impacted intersections.

(6) A statement of the total impact the projected generations will have on the existing level of service as determined and certified by a registered engineer.

(7) A sketch plan showing all existing driveways to public streets within 200 feet of the proposed development and all on-street parking or loading areas.

(8) Proposed site access driveways with a determination if a deceleration lane or taper is necessary based on current City warrant analysis standards, a determination if a left-turn by-pass lane is necessary based on a warrant analysis, and a sight distance study at the site access driveway.

(9) A pedestrian circulation plan showing all possible points of conflict between motorized traffic and pedestrian/bicycle traffic on public streets and sidewalks within 200 feet of the proposed development, or those intersections that may be impacted by the proposed development.

(10) A gap study for pedestrian or vehicular traffic may be required at non-signalized locations that may be impacted by the proposed development.


1:3 The traffic and/or parking impact analysis shall be reviewed by the Department of Transportation for completeness and accuracy.  The analysis shall include a determination of the service volume and capacity of adjacent streets including the traffic from the new development. The methodology to be employed in determining street capacities shall conform to the 1985 edition of the Highway Capacity Manual, Special Report Number 209, or the latest revision thereof. Proposals that will contribute traffic to streets or intersections that are or will be as a result of this proposal at a level of Service D, E, or F as defined in the Highway Capacity Manual may be denied by Commission and Council until such time as necessary street or traffic improvements are scheduled for construction.







City of Ann Arbor, 1997. All rights reserved.