Since 1932, Limboto Lake has been experiencing siltation, in 2006 it was measured that about 4.000 hectare of lake was covered. It was predicted by many that in 2031 Lake Limboto would disappear. The ‘Lake Limboto Revitalization’ has been conducted since 2017 by conducting many activities, including sabo plan implementation (also known as sabo technology). This study was originally conducted to review sabo plan in Limboto Lake, however this particular report was conducted to measure potential of erosion and sedimentation using WaTEM/SEDEM Model. Among 12 upstream rivers/Sub-DAS flowing into Limboto Lake, here were rivers with most potential to bring erosion and sedimentation into the lake to the least: Batulayar 193.662 m3, Biyonga Boluta 123.095 m3, Alo1 120.273m3, Alo 115.204 m3, Molamahu 73.058 m3, Marisa 57.075 m3, Pulubala 53.445 m3, Pone 40.254 m3, Molamahu1 39.585 m3, Pilolalenga 32.306 m3, Talumelito 32.247 m3, Pulubala2 31.267 m3, Tuladengi 28.908 m3, Pone1 27.306 m3, Payunga 26.746 m3, Biyonga Boluta1 25.895 m3, Pilolalenga1 21.841 m3, Tabongo 20.151 m3, Pulubala1 17.741 m3, and Tabongo1 11.031 m3. Considering the river dynamics as well as absence of secondary data about rivers, it was crucial to review sabo plan and to measure sedimentation potential per year.

The lahar flow  that occurred after the 2012  Gamalama Volcano  eruption, leading to the eastern valley flowing downstream  through the Togurara River to the center of Ternate City and Sultan Babullah Airport. To overcome the potential of  lahar  flow in the river since 2013 - 2016, several sabo dams and building facilities have been built. Based on the results of the calculation of deposits that potentially become lahar flows in 2016, the built-in capacity of the Sabodam has not been able to control the volume of sediment in the upstream of the river, then in the year 2017, 2018 constructed several additional Sabodam.  In order to determine the effectiveness, feasibility and conditions of the completeness of Sabodam, is done field assessment on 25 ~ 27 September 2018, the method used was a mathematical approach based on sabo technology. The assessment was in the form of a field survey, simple measurements, interviews with the Sabodam management agency and local residents related to the lahar flow that had occurred. With the capacity of several additional Sabodams built in series, the average river bed slope was originally 9.09% to 6.83%. After the construction of Sabodam, the maximum lahar flow was once as high as 7 m, but now it decreases do 4.2 m.   As the slope of the Togurara River slopes progressively, the lahar flow rate and its destructive power are reduced, so that Ternate City and Sultan Babullah Airport are spared from lahar disaster.Keywords: Lahar flow, sabodam, sabo technology, slope of riverbed, Togurara River.

Rawapening has an area of 2,667 acres, which now ceases to exist. This natural reservoir serves to preserve water, control flood, generate electric turbine, and raw water resource. The depth of this lake decreases 42 cm annually, with the shallowing could cause flooding of the lakeside and and reducing the water supply. This study finds the additional amount of structure and dimension of sabo dam to prevent hazards at each river: at Panjang 2 (B=20m H=2m, and B=25m H=2,5 m), at Galeh 2 (each of B=8m H=2,4m), at Legi 2 (B=10m H=2m, and B=25m and H=2,5m), at Parat 1 (B=13m H=2,7m), at upstream Sraten 1 (B=15m H=2,7m), at downstream Sraten 1 (B=15m H=2,7m), and at Kedungringgis 1 (B=12m H=1,8m). Existing materials are fine and rough sand. Using WaTEM/SEDEM, saboplan guideline by processing the designed capacity, it is estimated that each river’s potential annual yield (in tonnes): Panjang 86.221,8, Galeh/Torong 45.138,24, Legi 42.404,04, Parat 28.579,32, Sraten 25.988,76, and Kedung Ringis 6.955,2. Overall, sabo dam is designed to be a closed type dam located in inlet rivers of Rawapening. Sabo dam construction holds 25% of potential sediment. Collectively, it adds a control volume of 2.885 m3, from 11.539 m3 to become approximately to become 14.424 m3. To cope with sedimentation in Rawapening, the structural approachment (sabodam) should be combined with non structural approachment such as restoring land use in the upstream area for more optimal sedimentation control.Keywords: Sedimentation, rawapening, erosion, WaTEM/SEDEM

Ring net barrier is originally developed as a protection from rockfalls, but some countries have proven that this type is also effective in trapping debris flow sediment. In Indonesia, ring net barrier as sediment control is applied by Sabo Research and Development Center in Lumajang, East Java on a slope of 3.48o and is placed 0.8 m above the river bed surface. To identify the optimal position of the basal opening, a hydraulic flume test is performed with a scale of 1:60, 0.6 cm of diameter of ring, and a variety of discharge (11 liters/sec, 8 liters/sec, and 1.8 liters/sec). These numbers are based on the scaling with 10% sediment concentration and a flow time of 144 seconds. The basal opening position is varied from the same elevation as river bed, placed as deep as 1.66 cm and 3.2 cm The results show that ring net can retain more sediment if the net is placed 3.2 cm deep. Therefore, the sediment trap capacity of ring net barrier that is applied in Lumajang can be optimized by shifting the basal opening’s position to 1.92 meters deep from the river bed.