Dr. Conrad HeatwoleCenter for Watershed Studies

Virginia Tech, Blacksburg

Study watersheds – Magodi

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#0Luelo

MphiriKamwamphula

Kanyanga

Stream gage Weather station Rain gage Manual raingage

Paired Forest/Ag. Watersheds

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Khuyu school

Chazovu school

Kamwamphul

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Luelo

ZAWA

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Forested watershed

Agricultural watershed

Cropland expansion 1989-2007

1989Landsat

Cropland expansion 1989-2007

2002Landsat

Cropland expansion 1989-2007

2007Ikonos

Cropland expansion 1989-2007

Cropland expansion 1989-2007 1989Landsat

Cropland expansion 1989-2007

1989Landsat

Polygons are cleared areason May 2007 EnsoMosaic

Slope map of area

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Manga

Emusa EDP

Kanga Depot

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dsPaired

watersheds

Slope (%)

Slope calculated from 30m elevation grid derived from SRTM data using cubic interpolation.

Relation of cleared areas to landscape position

Maps of elevation and slope with the Enso cleared areas overlayed

Relationship between slope and cleared areas Cleared areas (digitized from 2007

Enso/Mosaic aerial imagery as seen in above slides) are overlaid on the slope map. Slope data is classified in 1% increments.

Areas at different slope values are tabulated. Cumulative areas determined and graphed as a % of the area.

Comparing slopes of cleared land in hill and plateau regions

Graph of cumulative percent area less than a certain slope

Data is only for cleared area on the 2007 Enso/Mosaic

Example – at 4% slope:45% of hill area and 83% of

plateau area is less than 4% Conversely, 55% of hill area

is greater than 4% slope, but only 17% of the plateau area.

Cumulative distribution of cleared area based on slope

Comparing slopes of cleared land for three watersheds

Observations: Kamwamphula is steeper than

Luelo; both are much steeper than the plateau area

While about 13% of the plateau watershed is greater than 4% slope, 45 to 60% of the hill area is

Cleared areas tend to the lower slopes, but surprisingly represent the range of slopes in the watershed.

cleared areas are not exclusively on the low slopes

The curves for the more fully cleared Luelo are closest, indicating that over time, cleared land represents the whole watershed – not just flatter areas

The curves for Kamwamphula are further apart, showing that initial clearing is on flatter areas. However, the trend seen in the Luelo is to be expected.

Cumulative distribution of area based on slope for a plateau

watershed and two watersheds in the hill region