Analysis Of Hydrological Erosion Risk

ANALYSIS OF HYDROLOGICAL EROSION RISK FOR THE ST. MARY BASIN, MONTANA, USA
Silvia Vittozzi
Master di 2° Livello in
“GIS e telerilevamento per la pianificazione Geoambientale”
UNIVERSITA’ DEGLI STUDI DI ROMA “ROMA TRE”
30 Giugno, 2008

THE PURPOSE OF RESEARCH
IS TO ESTIMATE
THE MOST EXPOSED AREAS TO SOIL EROSION
IN THE UPPER ST. MARY BASIN, MONTANA, USA
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WATERTON-GLACIER INTERNATIONAL PEACE PARK
Source: www.wikipedia.org
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Hydrology
Saskatchewan River watershed. Source:www.wikipedia.org
St. Mary River Km 200
Oldman River Km 362
South Saskatchewan Km 1,392 kilometers
Upper Old Man River watershed; in the South of the map, the affluent St. Mary river. Source: www.uoguelph.ca
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THE SOIL
Isbasicforall life’s form.
Encloseselements:
biological
mineral
Is a naturalresource
itneed long timetobecreated (geologicalages!)
Itneedtobeconserved
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Soilerosionby water
RAINFALL causesrills and sheeterosion
Fonte: Marco AcutisDiProVe, marco.acutis@unimi.it, www.acutis.it
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SOIL LOSS CAUSED BY WATER
Depend on:
amount and intensity of rainfall and runoff.
land cover which reduce the direct forces of rainfall
susceptibility to erosion (texture, composition,…)
topography of the landscape as described by slope length, steepness and shape.
Artificial conservation practices (terracing, canalizations) and land use.
THE GIS
IS A POWERFUL TOOL WHICH CAN MANAGE TOGETHER ALL THESE ELEMENTS
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DEM resolution 10 m
Fonte : USGS
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Mosaic of Natural-Color Aerial Photos, 2005These photos are in MrSID format and Montana State Plane coordinates, units meters, datum NAD83. Source: U.S. Farm Services Agency National Agricultural Imagery Program (NAIP).
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20 %
Subalpine fir Engelmann Spruce
15 %
Cliff/Talus Sparse Vegetation
16%
Dwarf-shrub/Herbaceous Complex Dry - Mesic
Source photos: USGS-NPS, 2007
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USLE
= UNIVERSAL SOIL LOSS EQUATION
Long terms (annual)
In a determinate area
In this case: Upper St. Mary watersheed
A standard methodtomapthe potentialrisk and erodibilityofsoil
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USLE
Itwasconceived:
In USA
In 1978
Wischmeier and Smith (USDA)
For the field.
Subsequently was applied also at not only agricoltural areas
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USLE
A = R * K * LS * C * P
A = potentialmeanannualsoil loss
R FACTOR = rainfallfactor
K FACTOR = soilerodibilityfactor
LS FACTOR = topographicfactor
C FACTOR = land cover factor
P FACTOR = conservationpractices (terracing)
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THE USLE MAP
It show:
The Potentialerosion
The areaswhere rise RILL EROSION and SHEET EROSION
UNITA’ In English Units: tons /hectar/year
DATUM: NAD83
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Shape file ottenutodallaclassificazione del data set: Vegetation Map - Waterton-Glacier International Peace Park Vegetation Mapping Project. USGS-NPS 1999 Glacier National Park-
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MEASURE UNITS
Conversion of USLE factor values to U.S. customary measure units.
Source: Wall et al, 2002.
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DATA SOURCES ofrainfall data:
United States Mean Annual R-factor,
1971-2000 spatial grid

Unitàdimisura : (100’s ft-tons in h-1 ac-1 yr-1) * 10
DATUM : WGS72
PRISM Group (Parameter-elevation Regressions on Independent Slopes Model) climate mapping

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DATA SOURCES soil
USDA State Soil Geographic (STATSGO) Data Base
for Montana

Coverage
NAD1927

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LS FACTOR
LUNGHEZZA DEL VERSANTE (length)
È un indice espresso sulla base di una condizione standard di:
9 ° di pendenza e 22 m di lunghezza
= Distanza compresa tra il punto in cui si origina lo scorrimento ed il punto in cui si ha una deposizione di materiale trasportato, per una diminuzione della pendenza.
PENDENZA del versante (stepness)
è espressa in GRADI
Definition of slope length (Renard, et al. 1987)
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Metodo Shulze (1995)
Formula per calcolare la lunghezza:
L =
where:
22.1 = misura standard dellalunghezza del versante
m = = esponenterelativo al rapportoerosionedaflusso e da rainfall
Where:
β =
Where:
SD = slope in degree
ʎ = - 3.0S + 100 for S < 25%
ʎ = 25 for S ≥ 25%
where:
S = slope gradient in percent
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ʎ = A
A = con (S ≥ 25,25,(5*(-3))+100)
β = B3
B3 = B1/B2
B1 = sin (SD div deg)
B2 = 0.0896(3*(pow(B1,0.8)) + 0.56)
m = M
M = B3/(1+B3)
L = pow(A/22.1,M) LENGTH
Formula per calcolare la lunghezza del versante: procedimento con rastercalculator:
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St = 10.8 sin (SD div deg) + 0.03 for S < 9%
St = 16.8 sin (SD div deg) – 0.50 for S ≥ 9%
St = 3.0 [sin(SD div deg)]0.8 + 0.56 for slope lengths < 5m
Con raster calculator:
S2 = con (SD < 9,(10.8*B1) + 0.03,(16.8*B1) – 0.5)
S3 = con (L < 5,(3*(pow(B1,0.8)) + 0.56,S2) STEEPNESS

Dopodichèsicalcolal’indice del fattoretopograficomoltiplicando la lunghezza per la pendenza del versante:
LS = S3 * L SL FACTOR
Formula per calcolare la pendenza del versante secondo queste condizioni:
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DATA SOURCES Landuse
USGS-NPS 1999 Glacier National Park Vegetation Map - Waterton-Glacier International Peace Park Vegetation Mapping Project. Shape file, NAD 83 .
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CANOPY