The Impact of sedimentation of mud, sand and rubbish on sustainability of the Asahan River, North Sumatera

The Asahan River, burdened by thick sedimentation, severely impacts the socio-economic fabric of Asahan Regency and Tanjungbalai. Shallow waters disrupt community life, particularly for fishermen, while the river’s estuary facilitates smuggling due to inadequate police and navy patrols. This study investigates the extensive social, economic, and environmental consequences of sedimentation on riverside communities and assesses its toll on economic activities at Teluk Nibung Port and Bagan Asahan Harbor.Conducted in four phases, the research involves data collection from local governments, a physical examination of the river, surveys and interviews with farmers and fishermen, and a Focus Group Discussion with community leaders. Findings highlight adverse effects on socio-economic life, including annual floods and a shift in livelihoods for some fishermen. Escalating rainfall trends over the past decades signal increased flood risks. Port activities show a decline, projected to cease within five years if unaddressed. Proposing dredging as a solution, the study advocates for restoring the economic conditions of Asahan Regency and Tanjungbalai while concurrently revitalizing the river’s ecosystem. The cost of flood mitigation underscores the urgency of intervention.


Introduction
Asahan River has been the source of livelihood for the community living by the both sides of the river and business, given the functionality and benefits of the stream.Asahan River is also a cheap, effective and efficient mode of transportation for business, export and import and social activities.However since the last 10 years Community life around the river is increasingly difficult, the river no longer provides a decent life especially for fishermen.Asahan River become sallow and at risk when high volume of rainfall combined with sediment at the bottom of the river that occupy the river's body, making the river shallower than it supposed to be.Water could no longer channel to the sea normally.Consequently, flooding often submerges settlements and surrounding areas.Flood has destroyed settlements, plantations, rice field, industries, schools, and road and bridge infrastructures [1].
The sedimentation of Asahan River obviously disturbs the system of local and national economy for its injuring impact to the export of commodities from Asahan and its surrounding districts.Moreover, it also IOP Publishing doi:10.1088/1755-1315/1302/1/012069 2 interfere the activities of sea patrols as Navy and Police experience obstacles in their work routine, Asahan estuary has been known as a smuggling area for goods and drugs.The objectives of this article is to explore a clear picture of sedimentation impacts on the social, economic and environmental issues faced by the community and also the impacts toward the economic activities at Teluk Nibung Port.

Materials and methods
Research was carried out in four stages.Phase 1, the researcher collected information from the Asahan district government and Tanjungbalai Government and collected data on economic activities at the Teluk Nibung Port.Rainfall data were obtained from the Bunut meteorology stations in Asahan downstream and Marihat in Simalungun upstream river.Phase 2, the researchers traced the Asahan river to see the river's physical condition and observed community activities around the Asahan river and Teluk Nibung port and Bagan Asahan Harbor.Phase 3, researchers conducted a survey by conducting interviews with farmers and fishermen using questionnaires.Phase 4, the researchers held a Focus Group Discussion (FGD) to determine community perceptions of sediment and flood problems.The FGD was held with community leaders, village head, NGO's and traditional figure at the Sei Kepayang sub-district office [3].
In executing the third step, researchers in particular collected primary data by interviewing community representatives through questionnaires.Purposive sampling is used in determining the respondent samples by following these criteria: Firstly, districts experiencing the impacts of sedimentation that the rivers pass through are determined.Secondly, from those districts, villages located exactly by the rivers are identified.The villages are chosen based on the discussion result between researchers, district chiefs, Agency of Environmental Affairs, and community elders of Asahan and Tanjungbalai.Thirdly, samples of farmers and fishermen are taken from each village to be interviewed with questionnaires.All villages selected are identified with geographical coordinates.Fourthly, a focus group discussion is held, engaging community representatives, district chiefs, sub-district chiefs, neighborhood chiefs, and the Agency of Environmental Affairs to capture ideas from relevant stakeholders.

Issue and the impacts of sedimentation 3.1.1. Rainfall intensity
The increasing rainfall intensity is seen from the data recorded on rain intensity in the upstream and downstream sides of Asahan River.In the river upstream, the condition is represented by the data retrieved from Marihat Research Station that has been recording rainfall intensity for 46 years (1972 -2018) [2].Meanwhile, rainfall intensity in the river downstream -Asahan Regency and Tanjungbalai City to be exact -is recorded by Bunut Research Station that has conducted data record for 27 years (1992 -2018).From both records given by those stations, the trends of rainfall and the monthly peak is presented on the graph below (see Figure 1 and Figure 2).Figure 2 shows a similar phenomenon on rainfall intensity between Bunut and Marihat.The peak points are as well happened on March, April, August, November and December.A high caution takes place at times when heavy rain happen simultaneously in both upstream and downstream sides of the river.In addition to that, the sedimentation that occurs in Asahan River would avoid the water flows, causing severe floods in Asahan Regency and Tanjungbalai City.Extreme weather phenomenon represented by rainfall parameter is hard to avoid as climate change is happening globally.However, efforts on dredging the Asahan River could reduce the harmful effect to the community.Dredging is one of the ways in adapting to the As shown in Figure 3, it is projected that for years to come, passenger and cargo ships would not be able to enter the Teluk Nibung Port.Two cold storage companies visited by the authors delivered complaints on their shrinking operations.To maintain their business, they have to send their commodities, such as frozen fish and shrimp, to Belawan Port using containers.This is a costly situation as they could not utilize Asahan River for exporting their products.Moreover, a captain of a passenger ship enroute to Malaysia under the line of PT.Pacific Jet star admitted this declining trend.Back in 2014, the company operated 5 ships.However, at present, only 2 ships left are operating at Teluk Nibung Port.This fact is accountable to the reports from the authority of ports and harbors as presented in Figure 4.
The load of exports and imports constantly falling.Starting in 2018, there are no more entry for imported goods at Teluk Nibung Port as shown in Figure 4 above.

Impacts on the community livelihood
A straight impact from physical sedimentation is not merely the obstructed flow of accessibility for cargo ships and fishermen boats.It also has a strong impact on the community living by the sides of Asahan River, notably when periodic floods (Rob flood and Keling flood) appear, with the upstream part of both rivers becomes the source.Also, two bridges built across Asahan River is unpassable for fishermen boats.
As this situation becomes a continuous problem, the autonomous government of Asahan Regency and Tanjungbalai City have repeatedly proposed to have the Asahan River be dredged.However, the implementation is still not present up to this report written.These evident impacts have been interrupting the daily livelihood of the fisherman and giving barriers to the activities in both Teluk Nibung Port of Tanjungbalai and Bagan Asahan Port.

Brief history of silting and dredging in Asahan River.
Previously, the Sultanate Asahan was centered at Bandar Pulau.The city of Tanjungbalai at that time 1620 was well known as a trading center and became one of the most significant ports for exports and imports in the eastern shore of Sumatera.As silting kept going in Tanjungbalai, the port was later moved to a closer area near the river downstream, presently identified as Teluk Nibung Port [4].
Furthermore, the Mayor of Tanjungbalai through a letter Number 050/19922/Bappeda/2014 has requested for support from the Governor to dredge the Asahan River.Unfortunately, until this report is written, the Governor has not responded to it yet.The most recent request was made through a letter from both the Regent of Asahan and the Mayor of Tanjungbalai Number 050/2722 on July 30, 2019 to the Minister of Environmental Affairs, the Minister of Public Works, and the Minister of Trade asking for immediate act on dredging.Yet, at times when low tides happen, the sand overlays in the downstream of Asahan River that looks like a wide desert.

The problems of legal basis of dredging the Asahan River
Recalling the Ministerial Decree of Public Works No. 04/PRT/M/2015 concerning the criteria of river areas (article 5), it is written that Asahan River is set as a strategic river area for national interest.Based on this decree, the previously mentioned Ministerial Decree of Trade No. 02/M-DAG/PER/I/2007 is not applicable on this case.Sedimentation has raised serious failures on the shipping line as well as caused flood in the community's settlements along the river [5].The Minister of Public Works could use his authority in managing water resources.The researchers conclude that this is the legal basis that strengthen the argument to dredge the river's sedimentation as explained below.Subsequently, after the local government obtains the principal permit from the provincial government, the proposed company that would perform the dredging must satisfy certain requirements.Besides having business approval, the company is obliged to have competent human resources.The company must implement the project by obeying the applied environmental and spatial laws as regulated on the Law No. 32 Year 2009 concerning protection and management of the environment; the Indonesian Government Regulation No. 27 Year 2012 concerning permission on environmental impacts (AMDAL); the Law No. 26 Year 2007 concerning spatial plans; and the Government Regulation No. 15 Year 2010 on the implementation of spatial plans.

Community perception towards the impacts of sedimentation.
For the last 20 years, endemic fishes have been hard to find.This situation is a serious disadvantage for the state because the sedimentation issue has caused the loss on biodiversity, river silting, and water contamination.As stated by the community's elders, some fish species, namely Siakap, Terubuk, Baung, Sibara, Benggong, Tapah, Tilan, Paitan, and Kalus that were abundantly present back then, are now scarce and rare to find.Some of these species are presumably faced extinction as discussed on the FGD session [6].
The major factor that caused stagnancy in economic and environmental development of the river's community is the flood as a result of sedimentation.Rob flood occurs every two years, while Keling flood -a flash flood -that create considerable damage happens 1 -2 times a year.During the flood, almost all houses are shrinking up to knee-long in height as discussed in the FGD session.Moreover, bad hygiene condition due to careless littering influences the environment as well.When the flood happens, the water carries solid wastes, attacking the residents' homes.This piling garbage is a threat that could trigger water borne diseases [7].
However, in the districts located at the downstream of the plaster -such as Tanjungbalai Selatan District and Teluk Nibung District in the city, as well as Bagan Asahan Village in the regency administrative areathe embankment is not constructed yet, thus these mentioned locations suffer from Rob flood and Keling flood whenever they happen.The disastrous risk is high as the flood would destroy the residents' settlements [8].Considering the climate phenomenon, the higher rainfall intensity gets, the bigger risk from flooding threatens the districts settled in the river banks, as presented on the graphs.Community awareness on this potential flood risk is already present, proven by their desire for the government to immediately work on dredging the sediments in Asahan River (based on the structured interview conducted for this study).The FGD that was held in the District Head's office hall [9].The FGD session has accommodated the community's voices on their expectation for the government to restore the ecological condition of the river.A 20% of the observed villages want to go back to the sea to catch fishes once the dredging in Asahan River has taken place (based on the interview).

Conclusions
If dredging does not take place immediately, the situation will continuously get worse.Floods will frequently happen that could destroy settlements, farms, schools, roads, bridges, and public facilities.The indication of this worsening situation comes from the rainfall prediction that lead to Rob flood and Keling flood from the rivers' upstream.The rainfall peaks are getting higher compared to previous decades, as seen from the graph that in the months of April, May, October, and November the highest intensity of rain fall.Meanwhile, on January, February, June, and December, awareness must be set as high alert as the weather could possible to happen due to climate change.Asahan Regency and Tanjungbalai City is highly vulnerable for disastrous events, bearing in mind the accumulation of sediments and the high intensity of rainfalls.Actually, if we interpret the concept of cost and benefit analysis, dredging will carry bigger economic value as sediments could be utilized domestically or to be sold to neighboring countries.The benefit of sediment has also non-monetary value such as flood will no longer occur, healthier and cleaner environment, and safer river traffic.In short, the benefits will flow for years, while the dredging costs will only be incurred once.

Figure 1 .Figure 2 .
Figure 1.Graphic on monthly water intensity for the last 46 and last 10 years

Figure 3 .
Figure 3. Trend of vessel in and out of Teluk Nibung Port

Figure 4 .
Figure 4. Volume of Domestic Good Loads at Teluk Nibung Port