River sedimentation of Batanghari River, geographically divides Jambi city, has resulted in urban flooding since almost the last 20 years. The river that functions as a source of water and a “water disposal site” from urban areas to downstream areas and finally to the sea. Here’s the report.
Aditya, 30, paused to rest. The motorcycle he was driving to go home every afternoon broke down in the middle of a flood on Jalan Pattimura in Jambi City, in the early afternoon of the second week of July 2022.
Fatigue appeared on the private employee’s face along with the fear that always comes when it rains.
“If it rains, then the flood will come,” he said.
These floods come suddenly and often spill onto the highway. To get home, Aditya has to wait for the motorcycle’s engine to dry. For that to happen, he will have push it out of the flood waters, about 1 kilometer.
“There’s no point in waiting. Floods usually take three hours or so to recede,” he said.
Floods are a threat to the residents of Jambi City, a busy port city along the Batanghari River on Sumatra, and flooding often reaches residential areas.
“Maybe this is called climate change. But, I do not understand,” he said.
According to the Office of Kimpraswil (Regional Settlement and Infrastructure) Jambi Province, the worst floods occurred in mid 2002 to 2003. At that time, flooding occurred in 62,410 hectares of agricultural areas, and 5,504 hectares of residential areas in Jambi City and in the districts of Muarojambi, Batanghari, Tebo and Kerinci.
Data from “Jambi in Figures 2022” published by the Central Statistics Agency states that Jambi Province covers 5.343.500 hectares, with a land area of 5.016.000 hectares. The city itself is in the middle and has an area of 20.543 hectares.
Jambi City is 23 meters above sea level and has an average rainfall of 3,218.4 millimeters per year. It is 150 kilometers from the coast but is downstream from Kerinci Seblat National Park, Bukit Tigapuluh National Park and Bukit Duabelas National Park.
Further downstream is Berbak Sembilang National Park, which stretches to the sea.
Batanghari Watershed
According to data from the Ministry of Environment and Forestry, the Batanghari Watershed (DAS) is the second largest watershed in Indonesia, covering a catchment area of about 4.5 million hectares.
The Batanghari watershed is an area bounded by topography that receives and collects rainwater, sedimentation and nutrients, then drains it through tributaries.
Conversion of land into oil palm plantation areas in many upstream to downstream areas has caused disruption of the “water absorption and storage” ecosystem in the soil.
“Choosing palm oil as a product that is sold to the international market only gives us a momentary advantage. The bad consequences of all of that have happened at this time and in the future,” said Abdullah, director of environmental NGO Walhi Jambi.
According to Walhi Jambi data, the palm oil industry in the province covers 1,363,426 hectares and is run by 186 companies, which are dominated by Muarojambi, Batanghari and Sarolangun Regencies.
“There is also a new trend where the palm oil industry has invaded forest areas, which are 290,378 hectares,” he said.
Not only that, industry has also caused massive forest and land fires in 2019, covering an area of 162,950.61 hectares.
“Jambi City is surrounded by the Muarojambi Regency area [and] its oil palm plantations. So it is only natural that if a flood occurs, the water will go to the central region, namely Jambi City,” Abdullah said.
The normal range for sedimentation, according to the Batanghari Control Agency (BP DAS) is 9 tons to 15 tons per hectare per year. But in the last 20 years, the sedimentation rate is estimated to be more than 100 tons per hectare per year.
Palm oil plantations
The opening of oil palm plantations in Jambi Province began in the early 1990s, and since then there have been forest fires and haze in the area.
Based on World Bank data in 1991, Indonesia has lost 40 million hectares of forest cover, resulting in a 30-percent decrease in forest area and a 180-percent increase in oil palm area from 1975 to 2005.
In the Batanghari sub-watershed, 54,225 hectares of forest have been converted to oil palm plantations from 1990 to 2010.
Without measures for solid and land conservation, planting oil palm on uneven ground will result in sedimentation, which leads to sediment blocking water flow along the river.
Read the first part of this article here (Bahasa Indonesia)
According to data from the Ministry of Public Works and Public Housing in 2021, the sedimentation of the Batanghari River area was at 6,185.25 tons per year.
Meanwhile, 4,588,700.16 hectares is considered critical land and has resulted in land erosion on 4,588,700.16 hectares.
In 2003, the erosion rate in the Batanghari watershed was around 5,891,000 tons and the amount of sediment at the Batanghari River estuary was at 521.86 million tons.
Damage to the river is estimated at 248 kilometers out of a total length of 775 kilometers.
According to the Jambi Province Flood Control and Coastal Protection Project, 608 hectares of the city are considered flood prone. Provincial data shows that flooding in 2021 affected 31 of 59 sub-districts and 30 housing units, more than in 2020, when only 17 urban villages were flooded.
Agus Sunaryo, head of the Jambi Provincial Bappeda regional planning body, said Jambi Province already has a Jambi Flood Control (JFC) program, which was implemented by the Sumatra River Basin Agency (BWSS) VI from 2013 to 2017.
He said the program includes four water systems — Teluk Lake, Tembuku River, Asam River, and Sipin Lake — that help reduce “the impact of flooding in the main river system or main drainage”
Jambi city is crossed by four sub-watersheds —the Kenali Besar River (68.06 square kilometers), the Asam River (28.63 square kilometers), the Tembuku River (24.23 square kilometers) and the Lake Mundung River (25.14 square kilometers) — and, Agus said, these bring hope that urban flooding can be controlled.
According to data from the PUPR Office of Jambi Province, there are 12 flood inundation points in Jambi City. These areas — the smallest has an area of 6.5 hectares and the biggest spans 140 hectares — are always flooded when it rains, with water reaching up to 30 centimeters and that take around three hours to recede.
Biopores for flood management
Kamir R Brata, a lecturer in soil science and land resources at the Bogor Agricultural University, offers a smaller-scale solution.
He says in a YouTube chanel “Video Biopori Official” that the most effective way to deal with urban flooding is to make biopore holes.
These holes, with a diameter of about 10 centimeters and a depth of 1 meter, are filled with organic waste, and work as water catchments in areas covered by asphalt and cement.
“With the biopore method, the biodiversity in the soil can process rainwater that falls and prevent flooding,” he said.
Biodiversity in the soil, he said, would create natural channels that no sophisticated technology could compete with. The organic waste serves as food for that biodiversity.
Aside from improving water absorption capacity of the soil, the holes also provide compost that can be harvested every six months.
As Jambi looks for solutions to its flooding problem, residents like Aditya will have to contend with the fatigue and fear that the rains will continue to bring.*
This report was supported by Earth Journalism Network (EJN) and Climate Tracker.
This article is part of Climate and Water Nexus Fellowship