04-04-2012 Planning Commission Work Session

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Stabilizing Your Shoreline to Prevent Erosion Page 2 of 6 retaining moisture-absorbing vegetation on the bluff outletting rain gutters and diverting surface runoff away from the bluff reducing runoff rate toward the bluff minimizing paved areas that increase runoff limiting ground water flow toward the bluff installing septic systems and drainfields away from the bluff avoiding additional weight on the bluff edge, such as pools, buildings, or storage sheds On property with steepslopes or bluffs, reducingthe amount of water reaching the bluff will help with p p Y stabilization. If diverting water away from the bluff is impractical, it should be routed through a nonperforated plastic drain pipe that outlets at the very bottom of the bluff. Rock should be placed around the outlet to prevent erosion at the bottom of the drain. Surface water and some ground water can be intercepted before it reaches the bluff by installing a "French drain" (Figure 2). KLPF KOCH Oran+ '.. Onsur,ay ky adds a tiaiGsr) GRAML�aKM PACSFILTILLI 5m nu GIILyVI Q�ry , rnernI.AT RPE •�_ real. - Figure 2: French drains intercept surface water and increase soil stability. Deeper drains will intercept more ground water, but shallower drains are effective also and may cause less disturbance on the bluff. The maximum depth for French drains is 15 to 20 feet. A French drain is a narrow trench set back from, but parallel to, the top of the bluff and filled with free- draining sand or gravel. A perforated, corrugated plastic pipe at the bottom collects water and should drain away from the bluff. The entire perforated length of pipe must be wrapped with fabric or a filter sock. Installing deeper drains will intercept more ground water and provide better protection for the bluff. No additional weight such as a building, garage slab, or vehicle should be placed near the top of the bluff. Septic systems and swimming pools are especially inappropriate near the top of a bluff because they add weight and water. For most property that slopes toward water, leaving the natural shoreland undisturbed is often the best and least expensive protection against erosion. A filter strip of thriving vegetation on and near the shore binds the soil and minimizes soil loss from surface runoff and waves, and from use by people (Figure 3). Existing vegetation can be enhanced by planting woody or aquatic plants. http://www.extension.umn.edu/di stribution/naturalresources/components/DD6946g.html 4/4/2012