BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

Like all BMPs, bulkheads and lake walls have advantages and disadvantagesdepending on the installation, purpose, and setting (Refer to Table 8-8).Table 8-8: Advantages and Disadvantages of Bulkheads and Lake WallsADVANTAGE• Protects backshore areas from wave actionand erosion. Stabilizes low bluffs.• Smaller footprint than a revetment.• Can help decrease turbidity and enhancewater quality by reducing the supply of finematerials from the backshore into the lake.• In marinas, allows boats to be moored closeto land.DISADVANTAGE• Protects only the land immediately behindthe beach. Provides no protection to thebeach and in some cases can increaseerosion at fronting and adjacent beaches.• Wave run-up and active erosion may begreater for a vertical wall than for arevetment.• Requires excavation, backfilling, pile driving,and material transport. In the short term, thiscan result in increased suspended solid loadswithin the adjoining water body.• May fail if scouring undermines the base ofthe structure.8.2.3 DESIGN CONSIDERATIONS AND PLANNINGSea walls (i.e. lake walls in this context) are most commonly used along oceanshorelines and are not common in Lake Tahoe. Bulkheads are designed to resistearth pressures from the backshore, rather than to resist high wave energy, andso are more common applications for Lake Tahoe. They retain low bluffs thatmight otherwise collapse towards the lake. If a bulkhead is placed at the toe ofan over-steepened bluff, the bluff may slide and bury or move the bulkheadtowards the water. In addition, bulkheads will not protect from rotationallandslides where the plane of failure is below the base of the structure. 20Steel sheet pile is the most commonly used bulkhead building material.However, good design practice also includes installation of a geotextile orgravel filter between the bulkhead and the backfill to further prevent sedimentlosses. An often-encountered difficulty in installing geotextiles is depth ofplacement. For sheet piles that are driven, placing the geotextiles the full depthof the structure is impractical. The loss of the backfill from water (rain and/orwave overtopping) seeping through a timber-constructed bulkhead to belowthe depth of the filter fabric or below the depth of the piles is a common modeof failure and can lead to structural damage. 21Sheet piles require suitable subsurface soil strength to support the weight of thestructure. Because they rely solely on the stability at the base of the structureto provide resistance to the upland forces bearing down on it, their application20USACE,1995, Engineer Manual EM 1110-2-1810, Engineering and Design: Coastal Geology andUSACE, 2008, Coastal Engineering Manual - Parts I-621USACE, 1995, Engineer Manual EM 1110-2-1810,Engineering and Design: Coastal Geology andUSACE, 2008, Coastal Engineering Manual - Parts I-6TRPA BMP HandbookCHAPTER 8: Shorezone Protective Structures and BMPs2012 8.2 Bulkheads and Lake WallsPage 8-25