Topography - BWCDDillustrate the topography of a field on a flat map; the height of each contour line is indicated on the map so that the hills or depressions can be identified depressions

TopographyTopographyTopographyTopographyBWCDD Zanjero TrainingBWCDD Zanjero Training

Session #5Session #5Session #5Session #51/30/20081/30/2008

SlopesSlopesSlopesSlopesA slope is the rise or fall of the land A slope is the rise or fall of the land s ope s t e se o a o t e a ds ope s t e se o a o t e a dsurface. It is important for the farmer or surface. It is important for the farmer or irrigator to identify the slopes on the land. irrigator to identify the slopes on the land. A l i i i hill A l i i i hill A slope is easy to recognize in a hilly area. A slope is easy to recognize in a hilly area. Start climbing from the foot of a hill toward Start climbing from the foot of a hill toward the top, this is called a rising slope. Go the top, this is called a rising slope. Go the top, this is called a rising slope. Go the top, this is called a rising slope. Go downhill, this is a falling slopedownhill, this is a falling slope

Expressing SlopesExpressing SlopesExpressing Slopes Expressing Slopes

The slope of a field is expressed as a The slope of a field is expressed as a The slope of a field is expressed as a The slope of a field is expressed as a ratio. It is the vertical distance, or ratio. It is the vertical distance, or difference in height between two difference in height between two difference in height, between two difference in height, between two points in a field, divided by the points in a field, divided by the horizontal distance between these horizontal distance between these horizontal distance between these horizontal distance between these two points. two points. The formula is: The formula is: The formula is: The formula is:

Slope NomenclatureSlope NomenclatureSlope NomenclatureSlope Nomenclature

SlopeSlope %%SlopeSlope %%

HorizontalHorizontal 0 0 –– 0.20.2HorizontalHorizontal 0 0 0.20.2

Very FlatVery Flat 0.2 0.2 –– 0.50.5yy

FlatFlat 0.5 0.5 –– 1.01.0

ModerateModerate 1.0 1.0 –– 2.52.5

SteepSteep < 2.5< 2.5

Cross SlopeCross SlopeCross SlopeCross Slope

Bench MarkBench MarkBench MarkBench MarkA bench mark is a permanent mark established in A bench mark is a permanent mark established in ppa field to use as a reference point. A bench mark a field to use as a reference point. A bench mark can be a concrete base in which an iron bar is can be a concrete base in which an iron bar is fixed, indicating the exact place of the reference fixed, indicating the exact place of the reference , g p, g ppoint. point. A bench mark can also be a permanent object on A bench mark can also be a permanent object on the farm such as the top of a concrete structure the farm such as the top of a concrete structure the farm, such as the top of a concrete structure. the farm, such as the top of a concrete structure.

Contour LinesContour LinesContour LinesContour Lines

A contour line is the imaginary horizontal A contour line is the imaginary horizontal A contour line is the imaginary horizontal A contour line is the imaginary horizontal line that connects all points in a field line that connects all points in a field which have the same elevation. A contour which have the same elevation. A contour line is imaginary but can be visualized by line is imaginary but can be visualized by taking the example of a lake. taking the example of a lake. Contour lines are useful means to Contour lines are useful means to illustrate the topography of a field on a illustrate the topography of a field on a flat map; the height of each contour line is flat map; the height of each contour line is flat map; the height of each contour line is flat map; the height of each contour line is indicated on the map so that the hills or indicated on the map so that the hills or depressions can be identified depressions can be identified depressions can be identified. depressions can be identified.

33--D MapD Map33 D MapD MapSuch a representation gives a very good idea of what the field looks like in reality. Unfortunately, it requires much skill to draw and is almost useless for the designing y q g gof roads, irrigation and drainage infrastructures. A much more accurate and convenient representation of the field, on which all data referring to topography can be plotted, is a map

22--D MapD Map22 D MapD MapIn hilly areas, the In hilly areas, the y ,y ,contour lines are contour lines are close together close together while they are while they are yywider apart on wider apart on flat slopes. The flat slopes. The closer the contour closer the contour lines, the steeper lines, the steeper the slope. The the slope. The wider the contour wider the contour lines, the flatter lines, the flatter the slopes. the slopes.

Map ScaleMap ScaleMap ScaleMap Scale

To be complete and really useful, a To be complete and really useful, a To be complete and really useful, a To be complete and really useful, a map must have a defined scale. The map must have a defined scale. The scale is the ratio of the distance scale is the ratio of the distance between two points on a map and between two points on a map and their real distance on the field. A their real distance on the field. A

l f 1 i 5000 (1 5000) l f 1 i 5000 (1 5000) scale of 1 in 5000 (1:5000) means scale of 1 in 5000 (1:5000) means that 1 cm measured on the map that 1 cm measured on the map corresponds to 5000 cm (or corresponds to 5000 cm (or corresponds to 5000 cm (or corresponds to 5000 cm (or converted into meters, 50 m) on the converted into meters, 50 m) on the field field field. field.

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Topography - BWCDDillustrate the topography of a field on a flat map; the height of each contour line is indicated on the map so that the hills or depressions can be identified depressions