| Summary: | Research for riverbed sediment was conducted in the Pabelan River Basin,
Progo Sub-basin, Central Java Province. The rivers in Pabelan River Basin
partially located in Merbabu Volcano, as a dormant volcano, and partly located in
Merapi Volcano, as an active volcano. Apu River, Tringsing River, and Senowo
River flows from Merapi Volcano and empties into the Pabelan River. In these
rivers, lahar frequently happens and always threatens farmland, settlements, and
public facilities. Therefore, since 1969 to 2009 has been constructed sediment
control. Community activities on the rivers that frequently happens lahar flow
include: agriculture, and sediment mining. The aims of this research are: (1) to
study the characteristics of granulometris distribution of the riverbed sediments in
Pabelan River Basin, (2) to study the characteristics of granulometris distribution
of the riverbed sediments in the upstream and downstream waterfall or Sabo Dam,
(3) to analysis the characteristics of granulometris distribution of the riverbed
sediments due to sediment mining, and (4) to determine riverbed sediments
management.
This research was done by using survey method with observation and
measurement, either in field and in laboratory. Observations were made on the
rivers at Merapi Volcano, rivers at Merbabu Volcano, and Pabelan River. The
sampling method was purposive sampling, while the analysis was performed with
descriptive statistical analysis.
The results are: (1) There is similar characteristics on distribution of
granulometris riverbed sediment in Merbabu Volcano, Merapi Volcano and
Pabelan River, i.e.: a) percentage of grain sediment size was highest in fractions
of small pebble, b) percentage of grain riverbed sediment sphericity was highest
in spherical class, and c) percentage of grain riverbed sediment roundness was
highest in round class. (2) The effect of Sabo Dam on the riverbed sediment
characteristics are: a) grain size riverbed sediment in the upstream is smaller than
downstream, except if there is any process differences, b) Sabo Dam have less
influence for distribution of grain riverbed sediment sphericity and grain riverbed
sediment roundness. (3) The sand mining on the upstream led to the scarcity of
sand in the downstream. (4) River management can be done by: a) a) Using
innovation technology for increasing of sand and stone value. b) Enforcement of
laws and regulations related to the river. c) Improving education for miner
families, so they can work outside the field of mining. d) Preservation of sediment
control and structuring of mining so did not cause rivers damage. e) Placement of
supervisors mining officer, who highly dedicated, honest and capable as a
negotiator.
|
|---|