DEWAN REDAKSI

Ketua Prof. Dr. Ir. Syamsulbahri, MS

Anggota

Prof. Dr. Ir. Moch. Munir, M.S (Unibraw-2008) Prof. Drs. Sutiman B. Sumitro, S.U. D. Sc (Unibraw-2008)

Prof. Dr. Ir. SM Sitompul. (Unibraw-2008) Prof. Dr. Ir. Luqman Hakim, M.S (Unibraw-2008)

Prof. Dr. Ir. Rustidja, M.S (Unibraw-2008) Dr. Ir. Nasir Saleh (Balitkabi Deptan-2008)

Penyunting Ahli

Ir. Arifin Noor Sugiharto, M.Sc, PhD (Unibraw-2008)

Ir. Didik Suprayogo, M.Sc, PhD (Unibraw-2008) Dr. Ir. Moch. Sahid (Balittas Deptan-2008) Brian O Flaherty (Ahli Bhs. lnggris-2008)

Dra. Francien Herlen Tomasowa, Ph.D (Lab. Bhs. Unibraw-2008) Drs. Adiono, M.A., PhD (Lab. Bhs. Unibraw 2008)

Penyunting Pelaksana

Drs. Sofy Permana, MSc, DSc. (Unibraw-2008)

AgustinaTri Endharti, S.Si., Ph.D (Unibraw-2008)

Sekretariat Pujiono SH

Alamat Redaksi/Penerbit

Lembaga Penelitian Universitas Brawijaya

Jalan Veteran, Malang-65145 Telp. (0341) 575824; 551611 psw. 301; Fak. (0341) 575828

e-mail Lemlitub@Brawijava.ac.id

Evaluasi Dan Parameterisasi Model Rains Pada Das Konto.

Resapan Air Sistem Agroforestri Damar (Agathis Dammara L)

Dengan Kedelai Dan Jagung

Syukur Makmur Sitompul,1) A.P. Utama 2) R. Rahman2) dan MTh. Sri Budiastuti 3) 1)Fakultas Pertanian, Universitas Brawijaya, Malang

2)Mahasiswa Fakultas Pertanian, Universitas Brawijaya, Malang 3)Fakultas Pertanian, Universitas Sebelas Maret, Surakarta

Abstrak

Diterima tanggal 26 September 2005

Disetujui tanggal 25 November 2006

Penelitian ini merupakan bagian dari suatu penelitian jangka panjang untuk mengembangkan

model hidrologi DAS Brantas di Jawa Timur dalam studi dan simulasi "rain absorption in natural systems

(RAINS). Penelitian dalam bentuk percobaan lapangan dilaksanakan pada hutan produksi Damar (Agathis

Dammara L.) dengan tekstur tanah pasir berlempung di Dusun Gombong, Ngantang, Malang yang

termasuk DAS Konto untuk menguji dan mendapatkan harga parameter model RAINS. Jenis tutupan lahan

yang dilibatkan dalam penelitian adalah agroforestri Damar+Kedelai dan Damar+Jagung pada lahan

dengan lereng < 10%, >10- 15% dan >15% di samping Damar monokultur pada lahan miring (>15%) yang

masing-masing diulang dua kali. Pengukuran infiltrasi dengan infiltrometer juga dilakukan untuk

mendapatkan koefisien resapan air potensial (Zref). Hasil penelitian ini menunjukkan bahwa tingkat

resapan air sangat bervariasi diantara curah hujan (11-99% dari curah hujan). Secara rata-rata, tingkat

resapan air dengan sistem agroforestri Damar ( 75%) lebih tinggi dari Damar monokultur (<70%). Curah

hujan merupakan faktor utama yang menentukan resapan air yang meningkat secara teratur dengan

peningkatan intensitas curah hujan. Model RAINS dengan (1-A ) = 0,8 yang tetap dapat menggambarkan

resapan air sebagai fungsi dari curah hujan pada semua sistem Damar yang diteliti. Harga parameter Z dari

model RAINS adalah 30,2 cm.nr1 untuk Damar mokultur, 32,6-33,8 cm.m"1 untuk Damar+Kedelai, dan

36,4-39,9 cm.m"1 untuk Damar+Jagung. Hubungan yang erat terdapat antara Zref, yang dihitung dari data

infiltrasi, dengan indeks tutupan lahan ( = Z/Zref). Ini mengisyratkan bahwa harga parameter Z dapat

diturunkan dari data infiltrasi seperti Z = 32,32+Zref atau Z = 30Zref°027 yang masih memerlukan penelitian

lebih lanjut.

Kata kunci: model hidrologi, resapan air, limpasan permukam, infitrasi, sistem agroforestri

Evaluation And Parameterization Of Rains Model On Konto Watershed. Water Absorption Of

Damar Agroforestry

Abstract

Evaluation and parameterization of rains model on konto watershed: Water absorption of damar

agroforestry: The present study is part of a long-term research to develop a hydrological model of Brantas

Watershed in East Java for the study and simulation of rain absorption in natural systems (RAINS). The

study in the form of field plot experiment was carried out at the production forest of Agathis dammara L

(Damar) with a soil texture of loamy sand at Gombong, Ngantang, Malang which belongs to Konto

watershed to examine and obtain parameter values of RAINS model. Land cover types involved in the study

were the agroforestry of Damar+Soybean & Damar+Maize at the slope of 0-10%, >10-15% and >15% in

addition to monoculture Damar at steep slopes (>15%) with two replicates for each combination. The

measurement of infiltration with an infiltrometer was also conducted to obtain the potential of water

adsorption (Zref). Results of experiment showed that water absorption rates varied considerably between

rainfall events (11-99% of rainfall intensity). On average, the rate of water absorption with the Damar

agroforestry systems ( 75%) was higher than with monoculture Damar (<70%). Rainfall was the main

factor determining water absorption which increased steadily with an increase in rainfall. The model RAINS

with a constant of (1- λ) = 0.8 was able to describe the absorpstion of water as a function of rainfall intensity

for the all of Damar systems under study. The value of Z parameter of RAINS model was 30,2 cm.m1 for

monocultre Damar, 32,6-33,8 cm.m1 for Damar+Soybean, and 36,4-39,9 cm.m1 for Damar+Maize. A close

relationship was found between Zref, generated from infiltration data, and land cover index(Ω = Z/Zref).

This suggests that the value of Z parameter is likely to be derived from infiltration data such as Z =

32,32+Zref or Z = 30Zref°027 which needs further investigation.

Keywords: hydrology model, water interception, runoff, infiltration, & agroforestry systems

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Today, October-December: 4-6.