Optimal sand removal capacity for in-stream mining
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Date
2016-09-01
Authors
Syamsul Azlan Salleh
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Abstract
River degradation due to excessive in-stream sand and gravel mining can be
attributed to lack of sustainable management. Sand is usually extracted directly from
river without proper guidance from concessioners which can lead unstable river
channel and excessive erosion in rivers as well as river banks due to uncontrolled
extraction of sand. In this study, the Acoustic Doppler Current Profile (ADCP) was
used to project river profile. By deploying the ADCP, the profiling of large river
cross section could be done easily and would improve the data accuracy in sediment
transport study. The characteristic in four rivers from soil laboratory analysis are
mostly sand and fine gravel (d50 = 0.8 to 2.0 mm). Three equations namely Ariffin,
Sinnakaudan et al. and Molinas-Wu were used to estimate total bed material load.
Ariffin equation has given the best prediction for four rivers with to 94.12%
accuracy for Sungai Perak, 71.43% for Sungai Kemaman, 66.67% for Sungai Pergau
and 75% for Sungai Kurau. The determination of suitable equations would be useful
for design stable channel, develop rating curve and determine sediment discharge in
river. From analysis, Sungai Perak was found to yield the highest sediment load
indicating its suitability for sand mining actvities. Electrical Resistivity Survey
(ERT) shows that riverbank subsurface consist of sand between 5 to 15 meter depth
based on projected profile. This implies that both floodplain and river islands can be
alternative sand mining sources. The sediment rating curve is used to estimate the
sediment recovery period and capacity of sand extraction from river. This study
infers that the sediment recovery period for two (2) meters extraction is about six (6)
days for a small river island and 98 days for a large river island.