Evaluasi Sensitivitas Parameter yang Digunakan dalam Model Prediksi Erosi Answers
SUMMARY
VERA AGUSTINA. Sensitivity Evaluation of parameters Used in ANSWERS
erosion prediction model. Supervised by Suria Darma Tarigan and Nailc
Sinukaban.
Many erosion predictions on watershed scale have been conducted by
scientists. The result of predicton will be accurate if the necessary data used in are
also representative. One of the erosion prediction model is Areal Nonpoint Source
Watershed Environtment Response Simulation (ANSWERS). The ANSWERS model
is one that uses distributed parameters to simulate correlations between rainfall and
sediment. The input data of model are rainfall, soil, land use and land surface
condition, characteristic of channel and individual element unit. Those input data
consist of parameters which show the characteristics of each element of the
watershed. The output goined from the model is runoff and erosion. The changing of
values within the parameters of input model effects output in varied levels. To know
the amount of changing levels in parameters values with different methods towards
the output, it is required that output sensitivity be evaluated towards the changing of
model input.
The purpose of the research is to evaluate the sensitivity of model output
towards any value changing of parameters of model input of erosion prediction.
The research began on September 1999 until Mei 2000. The soil example
was taken from research site is used for determining bulk density, total porosity, field
capacity and antecedent soil moisture. The meansure of permeability was conducted
on the site using permeameter.
Sensitivity analysis was done in several scenarios of simulation which are: (1)
the simulation of value changing of model parameters, (2) The simulation of the
chailging of rainfall intensity and (3) the simulation of the changing of watershed
size on runoff and erosion. Sensitivity analysis was conducted for 14 model input
parameters which are: total porosity (TP), field capacity (FP), the steady state
infiltration rate (FC), the different between the maximum and steady state infiltration
rates (A), infiltration exponent (P), infiltration control zone depth (DF), antecedent
soil moisture (ASM), soil erodibility (K), the potential interception volume (PIT), the
actual percentage of cover (PER), the roughness coefficient, the maxinlum roughness
height (HU). Manning's n (N) and relative erosiveness (C). Composition of the
simulation is: (1) parameters increase of 1% (Pl), 5% (P5), 10% (P10) and decreasing
it 1% (Ml), 5% (M5), 10% (M10); (2) rainfall intensity change simulation which
consist of 75 mm/hour (Cl), 100 m d h o u r (C2) and 125 mdhour; ( 5 ) the watershed
size change simulation which consist of 1.725 Ha (Ll) and 10.081.25 Ha (L2).
Sensitivity simulation result shows that runoff and erosion are decreasing
along the increasing of TP, FC, A, DF, PIT, RC, HU, K, C and decreasing of FP, P,
ASM. PER. According to the intensity value of many kinds of parameters value
change level, the 5% change levels is considered representative to determine runoff
and erosion sensitvity order. At the rainfall intensity C1 (75 d o u r ) parameters
order based on the runoff sensitivity is RC>ASM>FC>P>N>TP>FP>PIP
HU>DF>A> PER>K dan C.
Parameters order based on the runoff sensitivity with the increasing rainfall
intensity to C2 (100mm/hour) is RC>ASM>FC>N>HU>P>TP>DF>A>PI?,FP>
PER>K,C and C3 ( 1 2 5 d o u r ) RC>N>ASM>FC>P>TP>A>HU>DF>PI?,FP
>PER> K, C. Parameters order based on the erosion sensitivity with the increasing
rainfall intensity to C2 (100 mmlhour) is RC>FC>ASM>P>TP, A, DF, K, PIT, N,
C>FP>PER and C3 (125 mmhour) RC>FC>K>ASM>C>P>HU >N> FP, A>TP, DF,
PIPPER.
Parameters order based on the runoff sensitivity with the increasing of the
watershed size, with the watershed size L1 (1.725 Ha) and rainfall intensity C1 (75
m d l o u r ) is RC>ASM>FC>P>N>TP>FP>PIPHU>DF>A>PER>K
dan C, rainfall
intensity C2 (100 mmlhour) RC>ASM>FON>HU>P>TP>DF>A>PIPFP>PER
>K, C and C3 (125mm/hour) RC>N>ASM>FC>P>TP, A>HU>DF> PI?,FP>PER>
K, C; at watershed size L2 (10.081,25 Ha) with rainfall intensity C1 (75 rnmhour) is
RC>ASM>FC>P>HU>TP, FP>F, PIT>A>N>K, PER, C; with rainfall intensity C2
(100 mmhour) RC>FC>ASM>P>HU>FP>TP,A,N>DF,PIT,PER>K,C;
and rainfall
intensity C3 (125mrnljam) adalah RC>FC>ASM>N>P>FP,A>TP>DF>PIT>HU>
PER>K, C.
Parameters order based on erosion sensitivity at watershed size L1 with
rainfall intensity C2 (100 mmhour) is RC>FC>ASM> P, HU>TP, A, DF, K, PIT,
N>FP>PER and rainfall intensity C3 (125 mm/hour) RC>FC>K>ASM>C>P>HU
>N>P,A>TP, DF, PIT PER; mean while at watershed size L2 with rainfall intensity
C2 only RC which is sensitive and rainfall intensity C3 is RC>K, N, C.
Soil example taking method shows variaty of bulk density, total porosity and
field capacity. The result of permeability meansurement using permeameter tend to
be variatif. Antecedent soil moisture which was determined from disturb soil
example was less various at the same soil.
RINGKASAN
VERA AGUSTINA. Evaluasi Sensitivitas Parameter yang Digunakan dalam Model
Prediksi Erosi ANSWERS. Dibawah bimbingan Suria Darma Tarigan dan Naik
Sinukaban.
Berbagai prediksi erosi pada skala DAS telah banyak dilakukan para peneliti.
Hasil prediksi tersebut akan akurat apabila data yang digunakan representatif. Salah
satu model prediksi erosi adalah model Areal Nonpoint Source Watershed
Environtment Response Simulation (ANSWERS). Model ANSWERS mempakan
model dengan parameter terdistribusi yang mensimulasikan hubungan-hubungan
hujan limpasan dan hasil sedimen. Data masukan model adalah data curah hujan,
data tanah, data penggunaan lahan dan kondisi permukaan lahan, data karakteristik
saluran serta data satuan individu elemen. Data masukan tersebut terdiri dari
parameter-parameter yang menunjukkan karakteristik setiap elemen dari DAS.
Keluaran dari model adalah aliran permukaan dan erosi. Perubahan nilai parameterparameter masukan model mempengaruhi keluaran dengan berbagai taraf yang
berbeda. Untuk mengetahui seberapa besar taraf perubahan nilai parameter-parameter
dengan metoda berbeda terhadap keluaran, maka perlu dievaluasi sensitivitas
keluaran terhadap perubahan masukan model.
Tujuan penelitian adalah evaluasi sensitivitas keluaran model terhadap
perubahan nilai parameter-parameter masukan model prediksi erosi.
Penelitian dimulai pada bulan September 1999 sampai Mei 2000.
Pengambilan contoh tanah pada lokasi penelitian digunakan untuk penetapan bobot
isi, porositas total, kapasitas lapang dan persentase kejenuhan tanah. Pengukuran
permeabilitas dilakukan pada lokasi penelitian dengan menggunakan alat
permeameter.
Analisis sensitivitas dilakukan dalam beberapa tahap skenario sin~ulasi
sebagai berikut: (1) simulasi perubahan nilai parameter-parameter model, (2) simulasi
perubahan intensitas hujan dan (3) simulasi perubahan ukuran DAS terhadap aliran
permulcaan dan erosi. Simulasi dilakukan pada 14 parameter masukan model yaitu:
parameter porositas total (TP), kapasitas lapang (FP), laju infiltrasi konstan (FC),
selisih antara laju infiltrasi maksimum dan lconstan (A). koefisien eksponen
persamaan infiltrasi (P), kedalaman zone kontrol (DF), erodibilitas tanah (K), \;olcme
intersepsi potensial (PIT), persentase penutupan lahan (PER). koefisien kekasaran
permukaan (RC), tinggi kekasaran maksimum (HU). koefisien kekasaran Manning's
(N)dan faktor tanaman dan pengelolaannya (C). Susunan tahapan simulasi adalah
sebagai berikut: ( I ) parameter-parameter diubah dengan menaikkan 1% (PI), 5%
(P5), 10% (P10) dan diturunkan 1% ( 1 ) 5% ( 5 10% (Ml0); (2) simulasi
perubahan intensitas hujan terdiri dari: 75 mmljam (CI), 100 n~m/jam(C2) dan 125
m d j a m ('23); (3) simulasi peubahan ukuran DAS terdiri dari: 1725 Ha (LI) dan
10.081,25 Ha (L2).
VERA AGUSTINA. Sensitivity Evaluation of parameters Used in ANSWERS
erosion prediction model. Supervised by Suria Darma Tarigan and Nailc
Sinukaban.
Many erosion predictions on watershed scale have been conducted by
scientists. The result of predicton will be accurate if the necessary data used in are
also representative. One of the erosion prediction model is Areal Nonpoint Source
Watershed Environtment Response Simulation (ANSWERS). The ANSWERS model
is one that uses distributed parameters to simulate correlations between rainfall and
sediment. The input data of model are rainfall, soil, land use and land surface
condition, characteristic of channel and individual element unit. Those input data
consist of parameters which show the characteristics of each element of the
watershed. The output goined from the model is runoff and erosion. The changing of
values within the parameters of input model effects output in varied levels. To know
the amount of changing levels in parameters values with different methods towards
the output, it is required that output sensitivity be evaluated towards the changing of
model input.
The purpose of the research is to evaluate the sensitivity of model output
towards any value changing of parameters of model input of erosion prediction.
The research began on September 1999 until Mei 2000. The soil example
was taken from research site is used for determining bulk density, total porosity, field
capacity and antecedent soil moisture. The meansure of permeability was conducted
on the site using permeameter.
Sensitivity analysis was done in several scenarios of simulation which are: (1)
the simulation of value changing of model parameters, (2) The simulation of the
chailging of rainfall intensity and (3) the simulation of the changing of watershed
size on runoff and erosion. Sensitivity analysis was conducted for 14 model input
parameters which are: total porosity (TP), field capacity (FP), the steady state
infiltration rate (FC), the different between the maximum and steady state infiltration
rates (A), infiltration exponent (P), infiltration control zone depth (DF), antecedent
soil moisture (ASM), soil erodibility (K), the potential interception volume (PIT), the
actual percentage of cover (PER), the roughness coefficient, the maxinlum roughness
height (HU). Manning's n (N) and relative erosiveness (C). Composition of the
simulation is: (1) parameters increase of 1% (Pl), 5% (P5), 10% (P10) and decreasing
it 1% (Ml), 5% (M5), 10% (M10); (2) rainfall intensity change simulation which
consist of 75 mm/hour (Cl), 100 m d h o u r (C2) and 125 mdhour; ( 5 ) the watershed
size change simulation which consist of 1.725 Ha (Ll) and 10.081.25 Ha (L2).
Sensitivity simulation result shows that runoff and erosion are decreasing
along the increasing of TP, FC, A, DF, PIT, RC, HU, K, C and decreasing of FP, P,
ASM. PER. According to the intensity value of many kinds of parameters value
change level, the 5% change levels is considered representative to determine runoff
and erosion sensitvity order. At the rainfall intensity C1 (75 d o u r ) parameters
order based on the runoff sensitivity is RC>ASM>FC>P>N>TP>FP>PIP
HU>DF>A> PER>K dan C.
Parameters order based on the runoff sensitivity with the increasing rainfall
intensity to C2 (100mm/hour) is RC>ASM>FC>N>HU>P>TP>DF>A>PI?,FP>
PER>K,C and C3 ( 1 2 5 d o u r ) RC>N>ASM>FC>P>TP>A>HU>DF>PI?,FP
>PER> K, C. Parameters order based on the erosion sensitivity with the increasing
rainfall intensity to C2 (100 mmlhour) is RC>FC>ASM>P>TP, A, DF, K, PIT, N,
C>FP>PER and C3 (125 mmhour) RC>FC>K>ASM>C>P>HU >N> FP, A>TP, DF,
PIPPER.
Parameters order based on the runoff sensitivity with the increasing of the
watershed size, with the watershed size L1 (1.725 Ha) and rainfall intensity C1 (75
m d l o u r ) is RC>ASM>FC>P>N>TP>FP>PIPHU>DF>A>PER>K
dan C, rainfall
intensity C2 (100 mmlhour) RC>ASM>FON>HU>P>TP>DF>A>PIPFP>PER
>K, C and C3 (125mm/hour) RC>N>ASM>FC>P>TP, A>HU>DF> PI?,FP>PER>
K, C; at watershed size L2 (10.081,25 Ha) with rainfall intensity C1 (75 rnmhour) is
RC>ASM>FC>P>HU>TP, FP>F, PIT>A>N>K, PER, C; with rainfall intensity C2
(100 mmhour) RC>FC>ASM>P>HU>FP>TP,A,N>DF,PIT,PER>K,C;
and rainfall
intensity C3 (125mrnljam) adalah RC>FC>ASM>N>P>FP,A>TP>DF>PIT>HU>
PER>K, C.
Parameters order based on erosion sensitivity at watershed size L1 with
rainfall intensity C2 (100 mmhour) is RC>FC>ASM> P, HU>TP, A, DF, K, PIT,
N>FP>PER and rainfall intensity C3 (125 mm/hour) RC>FC>K>ASM>C>P>HU
>N>P,A>TP, DF, PIT PER; mean while at watershed size L2 with rainfall intensity
C2 only RC which is sensitive and rainfall intensity C3 is RC>K, N, C.
Soil example taking method shows variaty of bulk density, total porosity and
field capacity. The result of permeability meansurement using permeameter tend to
be variatif. Antecedent soil moisture which was determined from disturb soil
example was less various at the same soil.
RINGKASAN
VERA AGUSTINA. Evaluasi Sensitivitas Parameter yang Digunakan dalam Model
Prediksi Erosi ANSWERS. Dibawah bimbingan Suria Darma Tarigan dan Naik
Sinukaban.
Berbagai prediksi erosi pada skala DAS telah banyak dilakukan para peneliti.
Hasil prediksi tersebut akan akurat apabila data yang digunakan representatif. Salah
satu model prediksi erosi adalah model Areal Nonpoint Source Watershed
Environtment Response Simulation (ANSWERS). Model ANSWERS mempakan
model dengan parameter terdistribusi yang mensimulasikan hubungan-hubungan
hujan limpasan dan hasil sedimen. Data masukan model adalah data curah hujan,
data tanah, data penggunaan lahan dan kondisi permukaan lahan, data karakteristik
saluran serta data satuan individu elemen. Data masukan tersebut terdiri dari
parameter-parameter yang menunjukkan karakteristik setiap elemen dari DAS.
Keluaran dari model adalah aliran permukaan dan erosi. Perubahan nilai parameterparameter masukan model mempengaruhi keluaran dengan berbagai taraf yang
berbeda. Untuk mengetahui seberapa besar taraf perubahan nilai parameter-parameter
dengan metoda berbeda terhadap keluaran, maka perlu dievaluasi sensitivitas
keluaran terhadap perubahan masukan model.
Tujuan penelitian adalah evaluasi sensitivitas keluaran model terhadap
perubahan nilai parameter-parameter masukan model prediksi erosi.
Penelitian dimulai pada bulan September 1999 sampai Mei 2000.
Pengambilan contoh tanah pada lokasi penelitian digunakan untuk penetapan bobot
isi, porositas total, kapasitas lapang dan persentase kejenuhan tanah. Pengukuran
permeabilitas dilakukan pada lokasi penelitian dengan menggunakan alat
permeameter.
Analisis sensitivitas dilakukan dalam beberapa tahap skenario sin~ulasi
sebagai berikut: (1) simulasi perubahan nilai parameter-parameter model, (2) simulasi
perubahan intensitas hujan dan (3) simulasi perubahan ukuran DAS terhadap aliran
permulcaan dan erosi. Simulasi dilakukan pada 14 parameter masukan model yaitu:
parameter porositas total (TP), kapasitas lapang (FP), laju infiltrasi konstan (FC),
selisih antara laju infiltrasi maksimum dan lconstan (A). koefisien eksponen
persamaan infiltrasi (P), kedalaman zone kontrol (DF), erodibilitas tanah (K), \;olcme
intersepsi potensial (PIT), persentase penutupan lahan (PER). koefisien kekasaran
permukaan (RC), tinggi kekasaran maksimum (HU). koefisien kekasaran Manning's
(N)dan faktor tanaman dan pengelolaannya (C). Susunan tahapan simulasi adalah
sebagai berikut: ( I ) parameter-parameter diubah dengan menaikkan 1% (PI), 5%
(P5), 10% (P10) dan diturunkan 1% ( 1 ) 5% ( 5 10% (Ml0); (2) simulasi
perubahan intensitas hujan terdiri dari: 75 mmljam (CI), 100 n~m/jam(C2) dan 125
m d j a m ('23); (3) simulasi peubahan ukuran DAS terdiri dari: 1725 Ha (LI) dan
10.081,25 Ha (L2).