LWCE

use of resources with least waste or minimal waste

Conservation

keeping the quantity the same or not using

Preservation

is the detachment and transport of soil particles by natural (i.e. water and wind) or anthropogenic (man-induced or man-related) causes

Soil Erosion

the susceptibility of the soil to be eroded

Soil Erodibility

the capacity of rainfall to cause erosion

Rainfall Erosivity

rainfall/raindrop, runoff, wind

Eroding agents

Based on nature of occurrence

Natural erosion & Man-made erosion

Based on relative place of occurrence

Surface erosion & Subsurface erosion

Based on eroding agent

Water erosion & Wind erosion

Based on sequential occurrence

Sheet erosion, Interill erosion, Rill erosion, Gully erosion & Streambank erosion

Mechanics of soil erosion

Rainfall erosion, scour erosion, Gully erosion

is the uniform removal of soil in thin layers from sloping land, resulting from sheet or overland flow

Sheet erosion

is splash and sheet erosion combined

Interill erosion

is the detachment of soil by a concentrated flow of water

Rill erosion

produces channels larger than rills, called gullies, and which cannot be obliterated by normal tillage

Gully erosion

consists of soil removal from stream banks or soil movement in channel

Streambank erosion

includes detachment (by impact) & transport of soil by raindrop

RAINFALL EROSION

includes detachment (by scouring) and transport of soil

SCOUR EROSION

bigger than rills and can not be obliterated by ordinary tillage (repair is more on engineering works)

GULLY EROSION

fraction of sheet and rill erosion that actually reaches the reference point of discharge

Sediment Delivery Ratio (SDR)

planting along contours or land surface with same elevation

Contouring

alternate planting of 2 or more different crops along contours

Stripcropping

placement of crop residues, plastic, or other synthetic materials around the base plant or throughout the field to reduce evaporation from land surface

Mulching

grasses and other erosion-retarding vegetation planted alternately with rows of crops, along contours

Hedgerows and grass boundary

alternate planting of different crops on successive planting seasons

Crop rotation

reduces velocity and increasing time for infiltration

Terracing

This is applied for 25-30% slope and constructed along the contours into the hill slope in a step-like formation. It is used for maximum moisture conservation and where land is at a premium and difficult to farm

Bench Terrace.

Applicable for 9-24% slope

Zingg or Conservation Bench Terrace.

primary purpose is to remove excess water and minimize erosion. It reduces slope length and conveys intercepted runoff to outlet at a non-erosive velocity.

Channel Terrace

no grade in channel. Its primary purpose is moisture conservation and secondarily, control soil erosion. Its channel is normally closed at both ends to assure maximum detention. It is adoptable to deep, permeable soils and where outlet is a problem.

Ridge-Type

applicable for fruit trees and high-value crops

Orchard Terrace

impounding structures and reservoir - reduce velocity and modulate volume of water

Runoff Storage

Structure across a stream to control or divert the flow & Device for measuring the flow of water

Weir

water conveyance & control structure with a considerable slope, conveying water from a higher to a lower elevation

Chute

water conveyance & control structure with a 900 water drop

Drop spillway

water conveyance and control structure with water inlet mechanism

Drop inlet

cut-offs and detour channels

Diversion Channels

is a natural or artificial channel that shortens a meandering stream. The purpose of _______ is to increase the velocity, to shorten the channel length, and to decrease the length of levees

Cut-offs

is a synthetic permeable textile material used with soil, rock, or any other geotechnical engineering related material.

Geotextile

entrainment of solid material into a water body or channel and its further effects and consequences

Sediment Transport

process of deposition of sediment to downstream location

Sedimentation

rate of sediment flow (mass/time, i.e. kg/s)

Sediment Discharge

total mass of sediment, usually expressed per year (i.e. tons/year)

Sediment Yield

sediment or soil particle suspended in the water body and has more harmful effect due to its higher transportability

Suspended Load

sediment near or few inches from the stream bed and move by crawling or sliding

Bed Load

sediment transported by “saltation” or “jumping”

Saltation

the percentage of incoming sediment retained in the reservoir

Trap Efficiency

is a conduit in which a liquid flows with a free surface.

Open Channel

flow having a free surface and subjected to atmospheric pressure

Open Channel Flow

flow confined in a closed conduit, has no free surface and exerts no direct pressure but hydraulic pressure only

Pipe Flow

if the depth of flow does not change or if it can be assumed to be constant during the time interval under consideration.

Steady Flow

if the depth changes with time

Unsteady flow

if the depth of flow is the same at every section of the channel refers to Steady Uniform Flow

Uniform Flow

if the depth of flow changes along the length of the channel

Non-uniform Flow

together with gravity, they are the factor that basically affect open- channel flow

Viscosity

water particles appear to move in definite smooth paths or streamlines; and infinitesimally thin layers of fluid slide over adjacent layers.

laminar

viscuous forces are weak relative to inertial forces - water particles move in irregular paths which are neither smooth nor fixed

Turbulent

its effect upon the state of flow is represented by a ratio of inertial forces to gravity forces, given by the Froude Number

Gravity

include all watercourses that exist naturally on the earth

Examples: rivulets, brooks, stream, rivers, tidal estuaries, underground, streams

Natural

– those constructed or developed by human

Examples: navigation canals, power canals, irrigation canals, flumes, drainage ditches, spillways, floodways, chutes, roadside gutters

Artificial

usually a long and mild-sloped channel built in the ground which maybe lined or unlined

Canal

is a channel made of wood, metal, or concrete supported above the surface of the ground to carry water across a depression

Flume

channel having a steep slope

Chute

similar to chute, but the change in elevation is effected in a short distance

Drop

a covered channel of comparatively short length installed to drain water through a highway and railroad embankments.

Culvert

comparatively long covered channel used to carry water through a hill or any obstruction on the ground.

Open-Channel Tunnel

is the vertical distance of the lowest point of a channel section from the free surface

Depth of Flow (y)

is the elevation or vertical distance of the free surface above a datum * If the datum is the lowest point of the channel section, the _____ is equal to the depth of flow)

Stage

is the width of channel section at the free surface

Top Width (T)

is the cross-sectional area of the flow normal to the direction of flow

Water Area (A)

the length of the line of intersection of the channel wetted surface with a cross-sectional plane normal to the direction of flow.

Wetted Perimeter (P)

ratio of water area to its wetted perimeter, R= A/P

Hydraulic Radius (R)

ratio of the water area to the top width, D=A/T

Hydraulic Depth (D)

The flow specific energy is minimum for a given discharge and the discharge is maximum for a given specific energy

THE CRITICAL FLOW

1. The depth, water area, velocity, and discharge at every section of the channel reach are constant

2. The energy line, water surface, and channel bottom are all parallel, that is, there slope are equal.

THE UNIFORM FLOW

It is the formula generally used in open channel conditions.

Manning’s Formula.

These are lined and built-up channels which can withstand erosion satisfactorily. Lining material maybe stone masonry, steel, cast iron, timber, glass, and plastic.

Non-Erodible Channel

It is the velocity that will not start sedimentation and will not induce the growth of aquatic plants and moss.

Minimum Permissible Velocity

is governed by,

a. topography

b. the energy head required for the flow of water

c. purpose of the channel (for water-distribution purposes such as for irrigation, domestic water supply, and hydropower project, channels require a high level at the point of delivery, thus, a small slope is desirable in order to keep the loss in elevation to a minimum.)

Channel Slope and Side Slope

It is the vertical distance from the top of the channel to the water surface at the design condition. This is provided to prevent waves or fluctuations in water surface from overflowing the sides.__________ used in the design vary from 5% to 30% of the depth of flow.

Freeboard

is the greatest mean velocity that will not cause erosion of the channel body.

Maximum Permissible Velocity Method

is the pull of water on the wetted area. In a uniform flow, the tractive force is apparently equal to the effective component of the gravity force acting on the body of water, parallel to the channel bottom.

Tractive Force Method

The presence of grass or vegetation in channels will result in considerable turbulence which means loss of energy and retardance of flow. For earth channels used for carrying water on farm lands, however, a lining of grass is often found to be advantageous and desirable. The grass will stabilize the body of the channel, consolidate the soil mass of the bed, and check the erosion on the channel surface and the movement of soil particles along the channel bottom

Grassed Channels