Restoration and Management of Lakes and Reservoirs - Hydro-Environmental Analysis: Freshwater Environments - page 471

protect shorelines. McComas (2003), in his Lake and Pond Management Guidebook , described a
variety of shoreline protection and landscaping methods, including:

• Native landscaping and upland buffers

• Wave breaks for shoreline protection

• Biostabilization of the lakeshore

• Structural landscape protection (e.g., riprap, gabions, and retaining walls)

• Aquascaping, working with plants and woody debris in shallow water

There has been an extensive amount of literature and guidance on identifying and controlling
erosion and the consequent sediment loads from watersheds since that erosion often has multi-
ple negative impacts. Much of that literature, while not speciically focused on sediment yields
to reservoirs, is still applicable. But, as indicated by Morris et al. (2008), while erosion control to
reduce sediment is widely recommended to prolong a reservoir's function, it is dificult to imple-
ment successfully.

17.3.2 S edIMent S toraGe
Sediment storage simply refers to allowing for suficient or increased storage to accommodate sedi-
ment inlows and subsequent sedimentation. One commonly used method is to simply raise the
dam. Garbrecht and Garbrecht (2004; described by Morris et al. 2008) provided an example of
successively raising the Marib diversion over the period from 940 BC to AD 570 to accommodate
increased sediment upstream of the dam and an increase in land levels downstream due to diverted
irrigation water.

17.3.3 S edIMent r outInG
Sediment routing methods pass sediment loads around or through storage areas or structures while
minimizing deposition (Morris et al. 2008). Some of the pass-through methods include (Morris and
Fan 1998):

• Seasonal drawdown: where the reservoir storage is seasonally decreased to allow lows

representing high sediment loads to pass through the reservoir with reduced rates of sedi-
mentation (lower volumes, higher velocities, and lower retention time), and the reservoir is
reilled with wet season lows with lower sediment loads.

• Flood drawdown by hydrograph prediction: where instead of a seasonal drawdown, the

drawdown is timed to allow the passage of the leading edge or rising limb of a lood hydro-
graph where sediment loads are highest and the reservoir is then reilled during the lood
recession of the hydrograph.

• Flood drawdown by rule curve: A similar tactic for small reservoirs based on the reser-

voir's rule curve.

• Venting turbid density currents: In cases where a dense, sediment-laden plume “short-

circuits” the reservoir (passes through it without substantial mixing), the density current
may be intentionally vented through the outlet structure.

Some of the sediment bypass methods include (Morris and Fan 1998):

• Sediment bypass for instream reservoirs: where channels or tunnels are constructed to pass

sediment-laden lows around the instream reservoir.

• Off-stream reservoirs: where lows with high sediment loads are diverted to an off-channel

storage area and only relatively clear lows pass to the storage reservoir.