CHAPTER 10: EROSION AND RESERVOIR SEDIMENTATION

The natural process of soil and rock removal by wind, water, and gravity.

Erosion

Uniform removal of topsoil in thin layers over large areas.

Sheet (Inter-rill) Erosion

Small, temporary channels formed by concentrated runoff.

Rill Erosion

Large, permanent channels formed by deepening rills.

Gully Erosion

Erosion of riverbanks and streambeds by flowing water.

Channel Erosion

The total soil loss in a watershed, regardless of where the sediment ends up.

Gross Erosion

The amount of sediment actually leaving a watershed.

Sediment Yield

The ratio of sediment yield to gross erosion.

Sediment Delivery Ratio (SDR)

The most widely used equation for estimating long-term soil loss.

Universal Soil Loss Equation (USLE)

The USLE factor representing the erosive power of rainfall.

Rainfall Erosivity Factor (R)

The USLE factor indicating a soil’s inherent susceptibility to erosion.

Soil Erodibility Factor (K)

The USLE factor combining slope length and steepness effects.

Topographic Factor (LS)

The USLE factor representing influence of vegetation and cropping practices.

Crop Management Factor (C)

The USLE factor measuring the effectiveness of soil conservation practices.

Supporting Practice Factor (P)

Fine sediment in suspension that does not interact with the streambed.

Wash Load

Sediment originating from the bed and sides of a stream channel.

Bed Material Load

Coarser particles that move by rolling, sliding, or saltation along the bed.

Bed Load

Particles carried by turbulence but not continuously touching the bed.

Suspended Load

A graph showing how often different discharges occur in a stream.

Flow Duration Curve

A curve showing the relationship between discharge and sediment load.

Sediment Rating Curve

The percentage of incoming sediment retained in a reservoir.

Trap Efficiency

The sediment deposit formed at the river mouth inside a reservoir.

Reservoir Delta

The graph relating capacity–inflow ratio (C/I) to trap efficiency, developed from observed data.

Brune Curve

The average density of deposited sediments, typically about 1.3 tonnes/m³.

Sediment Density

The expected operational lifespan of a reservoir before sedimentation impairs its function.

Design Life (50–100 years in the Philippines)