Bahan Kuliah 3 (Faktor Erosi)

7/29/2019 Bahan Kuliah 3 (Faktor Erosi)

1/22

III. FACTOR INFLUENCING

EROSION


2/22

Secara hubungan fungsional, erosi terjadi

karena interaksi kerja dari iklim, topografi,

vegetasi dan manusia terhadap tanah

yang dinyatakan dalam persamaan

E= (i, r, v, t, m)


3/22

CLIMATE

Climate factors affecting erosion: Rainfall

Temperature

Wind

Humidity Solar radiation

Soil loss is closely related to rainfall partly through the detaching power of raindrops

partly through the contribution of rain to runoff Rainfall parameters related to erosion

Rainfall intensity the quantity of rainfall for a certain time period. i.e: mm/hr


4/22

Rainfall duration

Raindrop size and

distribution

Terminal velocity


5/22


6/22

Rainfall Erosivity

Is the potential ability of rain to causeerosion

Closely related to energy of rainfall (kineticenergy)

Formulas for kinetic energy of rainfall: Wischmeier and Smith (1958)

KE is kinetic energy in J/m2.mm and I is rainfallintensity in mm/h

In metric unit: Where KE in ton.m/ha.cm and I in cm/h

IKElog73.887.11


7/22

Hudson (1965) for tropical area

Zanchi and Torri (1980)

Onaga, Shirai and Yoshinaga (1988)

IKE

5.1278.29

IKE log25.1181.9

IKE log6.1081.9


8/22

Wischmeier and Smith (1958) : soil loss by

splash, overland flow and rill erosion is related to

a compound index of kinetic energy and

maximum 30-minute intensity (I30)called EI30 index

Hudson (1965) : erosion is almost entirely

caused by rain falling at intensity greaterthan 25 mm/h called KE>25 index


9/22


10/22

EI30 = 2,34 (CHm)1,98

Dimana R = erosivitas hujan bulanan,

(Rain) m = curah hujan bulanan (cm), nilai

R setahun diperoleh dengan

menjumlahkan RM selama setahun.


11/22

RE menyatakan rata-rata indeks erosivitas

hujan (unit/bulan), Q menyatakan rata-rata

jumlah hujan bulanan (cm/bulan), Pm

menyatakan rata-rata curah hujan

maksimal per hari (cm), dan D

menyatakan jumlah hari hujan per bulan.

349,0

678,0263,2

*056,40

*

D

PmQRE


12/22

SOIL

Correspond to soil detachability and soiltransportability

Erodibility : the resistance of the soil to erosion

Erodibility will suffer more erosion Erodibility varies with :

Soil texture

Aggregate stability

Organic matters

Shear strength

Infiltration capacity

Chemical content


13/22

Erodibility indices Wischmeier and Mannering (1969)

M : particle size parameter (% silt+% very finesand)x(100-% clay)

a : percent organic matter

b : soil structure code (1. very fine granular; 2. finegranular; 3. medium or coarse granular; and 4.

blocky, platy or massive c : profile permeability class ( 1. rapid; 2. moderate to

rapid; 3. moderate; 4. slow to moderate; 5. slow; and6. very slow)

)3(103.3)2(103.4)12(108.21003314.17

cxbxaMxK


14/22


15/22


16/22

VEGETATION

Vegetation acts as a protective layer or buffer betweenthe atmosphere and the soil

The major effects of vegetation in reducing erosion : Interception of rainfall by adsorbing the energy of the raindrops

canopy cover, and thus reducing surface sealing and runoff Retardation of erosion by decreased surface velocity

Physical restraint of soil movement

Improvement of aggregation and porosity of the soil by roots andplant residue

Increase biological activity in the soil

Transpiration, which decrease soil water resulting in increasedstorage capacity and less runoff


17/22

Varies with:

Season

Crop

Degree of maturity of vegetation Soil

Climates

The mean annual soil loss was 43 t/ha forbare plot, and 3.8 t/ha for the covered plot(Zanchi, 1983)


18/22

TOPOGRAFI

Topographic features thatinfluence erosion: Degree of slope

On steep slope resultingrunoff water is more

erosive and can moreeasily transport detachedsediment downslope

Mc Cool et al (1987) :slope steepness factor

for slope < 4 m for slope> 4 m and s < 9 % for

slope > 4 m and s 9 %where : field slopesteepness in degrees =tan-1(s/100)

s = field slope in percent


19/22

Length of slope

Longer slope were

more runoff

accumulates and

greater erosive forces

McCool et al (1989) :

length factor

l : slope length in m

m

lL

22

05.0)(sin269.0sin

sin8.0

m


20/22

Wischmeier and Smith (1978) formulating

slope and length factor as:

n : 0.5 for convex slope, 0.4 for straight

slope and 0.14 for concave slope

)0065.0045.0065.0(13.22

2

ss

l

LS

n


21/22

Shape of slope

Convex. The intensity

of erosion processes

reach the maximum at

the bottom part Concave. The intensity

of erosion processes

reach the maximum at

the end of the upper

part straight (uniform)

combine


22/22

HUMAN

Dari semua faktor di atas, faktor manusialahyang sebenarnya paling menentukan apakahtanah yang diusahakannya akan rusak ataulestari. Banyak faktor dari manusia yang

menentukan perlakuan manusia terhadapsumber daya tanah, antara lain: (1) luas tanahpertanian yang diusahakan; (2) sistempengelolaan yang dilakukan; (3) statuspenguasaan tanah; (4) tingkat pengetahuan dan

penguasaan teknologi; (5) harga produkpertanian; (6) pajak; (7) pasar dan inputpertanian; dan (8) infrastruktur dan fasilitas.

Bahan Kuliah 3 (Faktor Erosi)

Documents

Transcript of Bahan Kuliah 3 (Faktor Erosi)