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Ravine and lakefront properties are fragile lands which require special care if they are to be preserved for current and future residents. This brochure will identify the specific problems that homeowners in ravine and lakefront communities face, explain some of the causes of these problems, and suggest methods that will help homeowners keep their property and their neighbors' properties in the best possible condition. The brochure will also explain how to preserve the integrity of the ravines and lakefront, and what features you should be aware of as a homeowner or prospective homeowner. Please note: In addition to the guidelines presented in this brochure, many communities have adopted ordinances which regulate grading, landscaping and other activities which homeowners may undertake. Be sure to check with your local government to find out if any such regulations apply to your property.

Not many localities in the country enjoy the vast ocean-like panorama of Lake Michigan at one's doorstep, or the wooded and flowering beauty of ravines off one's back yard. Because of this unique beauty, ravine and lakefront properties are desirable locations for homes. Some ravines contain rare and endangered plant species and may be justly considered ecological treasures.

But erosion can destroy anything, and water can erode with startling rapidity. Water erosion is the most threatening force impacting ravine and lakefront property. It is a natural force which can be slowed, but cannot be stopped entirely. Over geologic time, mountains have been thrust up 10,000 feet and then eroded completely away. Even in the last 100 years erosion has, for example, claimed 50 to 100 feet of lakefront land that had at one time been on the bluff in Highland Park but now lies at the bottom of Lake Michigan. The damage is accelerated when additional erosion is caused by human activity; this type of erosion-causing activity can and should be controlled.

This brochure will discuss the potential damage resulting from water erosion and will present methods to prevent this damage to the greatest extent possible.

GEOLOGY OF THE BLUFFS AND RAVINES

Ten thousand years ago the last glacier covered most of Lake County with ice. When the ice moved here from the north, it carried with it rocks, boulders, clay and sand that it had scoured from the soil as it made its way south. When the atmosphere warmed and the glaciers melted, it left this material--called glacial till--on top of the previous surface. As rainwater ran off this new surface, over time it gouged out large gullies that we call ravines. The clay in the glacial till is very tough and can support heavy structures such as buildings and swimming pools--until it gets wet. Underneath the clay, there are layers of sand and gravel scattered at various depths. Water tends to travel along the seams of these different layers making the layers more prone to slippage. When severe slippage occurs, the entire top layer can start to slide away, carrying with it any structures or trees that were on it. As a result, the point where these seams intersect the bluff or ravine slope are subject to periodic movement.

The glacial till tends to be stable if the slope is about 35 or fewer degrees from the horizontal. If the slope is steeper, it is inherently unstable and tends to collapse. Unfortunately, much of the lakefront is on a bluff whose slope is steeper than 35 degrees, and many ravines have sides that are steeper than 35 degrees. Since this is an unstable condition, every precaution must be taken to eliminate factors which aggravate this instability, and to provide reasonable means to enhance stability. How to do this will be discussed later in this brochure.

EROSION AND OTHER DAMAGE IN RAVINES

Ravines formed by geologic weathering serve as natural drainage channels. Rainfall drains into the ravines and forms a stream at the bottom which empties into Lake Michigan. This stream of water can cut a channel at the bottom of the ravine, but, as long as the velocity of flow remains low, the cutting of this channel is very slow. Due to urbanization, however, ravines serve today as conduits for much larger volumes of water, and the larger volumes travel at much higher velocities.

Any construction of impervious surface--buildings, patios, driveways--covers the natural surface of soil which could otherwise absorb large quantities of water. But when impervious surfaces replace the natural soil, the water can only drain off into the ravines, increasing not only the total volume of water but also increasing the velocity of the water down the sides of the ravines and into the channels at the bottom.

This higher rate of flow does much more damage than a slow rate. (Erosion is proportional to the square of the velocity.) It does damage to the slopes and damage to the bottom of the ravine which is eroded more rapidly into deeper and deeper channels. When the channels get deep enough, the soil just above is undercut and weakened. This weakened soil often slumps, carrying debris into the channel, together with trees and shrubs that were growing there. If the channel becomes blocked, the diverted water will create a new channel and succeeding rainfall may create damage to new areas.

Automatic lawn sprinklers, especially near the edge of the ravine, often contribute to erosion if they are set to go on at regular designated times. If the ground is already saturated by a heavy rain, additional water coming from an automatic sprinkling system only aggravates over-saturation of the ground and causes the spillage of water, called "sheeting," over the edge and into the ravine.

In the many areas, rainwater collected from streets into storm sewers discharges into the ravines. The amount of flow from a major storm can be tremendous, pouring large volumes into the ravines at high velocity. These major storms are main contributors to ravine erosion.

Vegetation on the slopes of ravines is very important, for the root systems tend to hold the soil together. Destroying the vegetation will rapidly increase erosion on the slopes. Vegetation can be destroyed or injured by constant trampling, by heavy machinery, by dumping material such as lawn wastes on top of it, by heavy flow of water such as from a pipe opening or break at some point on the slope, by overhangs that create a shadow and prevent light from reaching the plants, and by misguided attempts to stabilize the slope by inappropriate methods.

Another source of instability arises from the pressure created by construction too near the top edge of the ravine. As mentioned, there are sand layers scattered in the soil which form weak spots. When there is too much pressure on the surface, the clay may slide away and the soil under the pressure area can slump into the ravine, carrying the structure with it. Also, heavy machinery used too close to the edge may put excessive pressure on the soil which may then fail.

A further hazard which contributes to ravine instability is excessive moisture on the ground. Water which cannot drain away saturates the soil, making it more prone to movement and slippage.

Eventually, when the slope angle of the adjacent ravine is too steep, the saturated soil may give way and slump into the ravine. This exposes bare soil where the slump had occurred, and this bare soil is very vulnerable to further erosion by water.

Finally, excessive runoff of water down the slope (sheeting) often occurs after very heavy rain and is very detrimental to the soil on the surface of the slope.

Methods that can be used to minimize the damage from water and from loss of vegetation (See below).

EFFECTS OF EROSION ON BLUFFS

All of the ravine problems described in the preceding section also impact the bluffs overlooking Lake Michigan, but bluffs are subject to one additional hazard: the action of waves at the bottom of the bluff or "toe".

Large waves are one of the most powerful forces of nature, and therefore, potentially one of the most destructive. A wide beach at the bottom of the bluff is the best protection against wave action, as it dissipates the energy of the waves as they roll up the beach.

Unfortunately, high levels of water and sand loss in the lake have narrowed the beaches so they are no longer able to keep the waves from reaching the toe of the bluff. When the waves do hit the bluff, they scour out the toe of the bluff, gouging into it a line of cliffs, or scarp, which undermine the bluff.

Sooner or later the soil over these scarp will collapse, leaving bare soil which is even more vulnerable to further erosion. Unless the beaches are artificially "nourished" with sand from other sources, or the water returns to very low levels, these problems will only worsen.

High waves are the result of major storms, with winds blowing from the northeast. A "100-year storm"--one with the highest waves recorded, and so named because they occur very seldom--will create gigantic waves which in a few hours can tear out great volumes of soil. Even a "20-year storm," with waves of 15 feet, can wreak enormous damage to the toe of the bluff.

Over many years a protective device called a groin, which consists of a steel bulwark installed at intervals perpendicular to the shoreline, has been used to interrupt the transport of sand. Other protective measures may be more effective.

Before buying:

• Inspect the slopes thoroughly. Look for denuded vegetation, slumps and gullies.
• Check the angle of the slopes (whether steep or shallow), and the nearness of structures to the edge of the slope.
• Get advice from a structural or soils engineer familiar with ravines.

NEW CONSTRUCTION

Before any new construction or remodeling is begun, a permit is almost always required. If construction is contemplated on land adjacent to ravines or bluffs, it is imperative that you read and understand any ordinances covering this type of construction. Any construction planned near the edge of the slope may require an engineering study. This involves testing of soil borings to determine the nature of the soil at various depths and the advice of a structural and/or soils engineer familiar with ravines. In general it is undesirable to build too close to the edge, to have overhangs, or to build into or onto the slope.

During construction, materials should not be piled up near the edge of the slope; insist they be placed at least 20 feet from the edge. The same applies to material and debris from demolition of existing structures or earth that is removed.

Trees that are to be preserved should have their roots protected from excessive weight resulting from piles of materials or heavy machinery. It is best to place a fence around these trees to alert workers. If it is necessary to disturb a tree or cut some of its roots, consult a landscape architect as to the best means of keeping the tree alive. Some communities have an ordinance regulating the removal of trees; it is essential to be familiar with such an ordinance before any construction is contemplated.

In the event that vegetation needs to be removed or disturbed in order to store construction materials, do not remove the vegetation more than 15 days prior to the beginning of construction. Disturbed soil should be covered with erosion control fabrics and replanted as soon as possible to prevent erosion.

If fire or other damage occurs to a part of a structure, before rebuilding in the exact footprint of that structure, evaluate the possibilities for changes such as creating a setback from the edge of the slope, or other changes that would make the new construction more in line with good practice.

HOW TO MINIMIZE DAMAGE TO YOUR PROPERTY AND TO YOUR NEIGHBORS' PROPERTIES

• Do not set automatic sprinklers which are near the edge of the ravine or bluff to go off at regular intervals. Turn them on manually only when the soil is dry. If the soil is saturated from a heavy rain, sprinkling automatically not only wastes water but contributes to erosion caused by water flowing down the sides of the slope.
• Slope patios and pavement so that they drain toward the street and not toward the ravine or bluff. By sloping these structures away from the slope, less water will drain directly over the surface of the ravine or bluff. Water run-off, especially sheeting, weakens and erodes soil from the surface.
• Drain runoff from the roof of buildings into storm sewers, or direct it by hose to the bottom of the ravine or bluff. If the runoff from the roof gutters is allowed to drain over the edge of the ravine or bluff, it will tend to create gullies which will further erode during storms when runoff volume and velocity are great. If drainage into storm sewers is not possible, the runoff should be directed toward the street. Alternatively, the runoff can be collected in a large hose (elephant hose) which lies on the surface of the bluff or ravine and leads all the way to the bottom. At the bottom, the outflow should be directed to a layer of large stones so that the energy of the flow is dissipated and the flow does not wash away soil.
• Do not build swimming pools within 20 feet from the edge of the ravine or 50 feet from the edge of the bluff. Because swimming pools have a tendency to leak as they age they should be installed further away from the slope edge than other structures.
• Use terracing on the slopes only for stabilization, not for gardens or sitting areas. Don't let inexperienced workmen attempt terracing for slope stabilization. Permits are usually required for any construction on slopes. Terracing requires experts. Small terraces, with walls up to 4 feet can be done economically with unit paver wall systems which do not rot. Wood on grade is not recommended. Larger terraces require engineering studies. Terraces should be promptly vegetated.
• Revegetate bare spots on the slope using plants that are best suited to the conditions of your ravine. Ravines are generally quite shaded and require plants that grow well with little direct sunlight. The list below presents some plants that are recommended for ravine restoration. For a more complete list, refer to the City of Highland Park brochure, Planting in Ravines, or consult a landscape architect who is familiar with ravine vegetation.

Recommended Plantings:

Shade Trees:
Sugar Maple, White Ash

Intermediate Trees:
Serviceberry, Hornbeam

Shrub Trees:
Witchhazel
Dwarf Bush Honeysuckle

Grass and Sedges:
Pennsylvania Sedge
Bottlebrush Grass

Wild Flowers:
May Apple, Trillium
Meadow Rue

Ground Covers:
Wild Ginger, Native Ferns

• Inspect bluffs and ravines periodically and plan for routine maintenance. Regularly clean out debris from the ravine channel. If they dont obstruct the flow of water through the channel, dead trees can be left. If trees are cut, the stump should be left in the ground since the root structure will continue to contribute to slope stability. Gullies should be filled with soil and replanted. Don't fill gullies with debris--it will simply wash away. Correct the condition that led to the gullying. Large devegetated areas can be covered with a special fabric which can stabilize the slope until vegetation can be established.
• Don't allow heavy machinery into the ravine, or even light machines with treads. If motorized equipment must be used, use rubber-tired vehicles only.
• Use the greatest care when draining pools. Pools are best drained via a hose leading to the street. Leaking pools can create severe damage to the underlying soil, so repair leaks promptly. When draining pools, the rate of drainage should be limited so that excessive water does not find its way, via storm sewers, into the ravines. A garden hose is ideal as it limits the flow adequately.
• Inspect hose or pipe leading to the bottom of ravines at least twice a year. Old clay pipe is brittle and slight movements of the earth can disrupt it. If breaks or leaks do occur, clay pipe is very difficult to repair. It is best to replace clay pipe with elephant hose. The hose should lie on the grounds surface and not be buried. Leakage from existing pipe is a major contributor to erosion of slopes. Never drain water onto the surface of the ravine or bluff.
• Consult a professional experienced with ravine vegetation prior to removing or planting trees in a ravine. Due to their root structures, trees contribute to slope stability. City regulations require that a permit be obtained to remove any tree with a diameter of 8" or more. However, even the roots of much smaller tree make an important contribution to slope stability in a ravine and lake bluff community. Therefore, it is important to get expert advice prior to removing even these small trees. In addition, non-native trees which have been introduced into the ravine environment tend to develop dense canopies which block the sun and kill underlying vegetation. Therefore, it is also important to select native species when planting new trees. Consult a professional experienced with ravine vegetation, then call the City Forester at the number listed on the back of this brochure prior to removing or planting trees in a ravine.
• Protect the shoreline. Protection of the shoreline is a complex and expensive enterprise. If it is not done properly, it can cause further damage to one's own property and to neighbors' property. The least expensive protection is offered by installing large boulders at the toe of the bluff. If several neighbors cooperate to protect their shoreline, the cost is less and the results better. The boulders absorb the energy of the waves so that water reaching the soil does not have the destructive force it would otherwise have. When the level of Lake Michigan is high--and it can vary by 6 feet over several years--the beaches are narrower or non-existent, and the potential for damage by wave action very great. It takes but one major storm to do extensive damage to the bluff. There are other protective devices, such as steel walls, that can be effective, but costs can be prohibitive. Coastal engineers must be consulted before making any decision, and permits are required.
• Do not build structures close to the edge of the slope, nor cantilever them over the slope. The ground near the top edge of the slope is the most unstable and vulnerable part, and in general, buildings should be set back 20 feet or more. Buildings should not be erected out onto the slope because cantilevered structures prevent light from reaching the soil. Without this light, vegetation is destroyed and the soil is much more likely to erode.
• Do not permit heavy machinery to be used within 10 feet from the slope edge. The process of construction and use of heavy machinery may cause failure of the vulnerable ground at the edge of the slope, and heavy structures will hasten the failure of this vulnerable area.
• Have good, solid vegetation at the top edge of the ravine or bluff. If there is a flower bed there, plant it thickly. Do not turn over the soil so that bare soil is exposed. Thick vegetation helps hold the surface soil in place. It also purifies the water that runs over it, minimizing harmful bacteria entering Lake Michigan. Turning over the soil and leaving it bare promotes erosion.
• Never dump lawn clippings, leaves, debris, or waste into the ravine or onto bluffs. Lawn clippings and leaves form a mat which covers the natural vegetation and smothers it. In some communities it is illegal to dump anything into ravines.

• best water management,
• good vegetation, and
• proper set-backs from the edge of the bluff.

For more information regarding Highland Park regulations including stormwater management, tree preservation and zoning, contact:

For more information regarding stormwater management and erosion control techniques, contact:

Lake County Stormwater Management Commission
333-B Peterson Road
Libertyville, IL 60048
(847) 918-5260

Northeastern Illinois Planning Commission (NIPC)
222 S. Riverside Plaza, Suite 1800
Chicago, IL 60606
(312) 454-0400

Lake County Soil & Water Conservation District (SWCD)
70 S. U.S. Highway 45, Suite 205
Grayslake, IL 60031
(847) 223-1056