EXPLANATION OF WATERSHEDS

Watersheds are formed from a collection of rivers in a basin system with a outflow or single estuary. Watersheds are water container areas that enter into larger river water areas and end at an output (estuary). The watershed area boundary is measured by connecting the highest points between the watershed with one another. Between one watershed and other watersheds are usually restricted by ridge paths in the form of hills or mountains. The two boundary areas of the watershed are known as the River Flow Limits.

Many watershed areas in Indonesia are now in critical condition. Some forest areas, especially in the upper reaches of the river, have turned into shrubs, even bare or almost without trees. Until now the watershed damage continues.

The problem of watersheds in Indonesia is now mostly focused on floods that repeatedly afflict areas that occur in the lower / flat areas. This not only caused land productivity to decline, but also caused problems of deposition of mud and soft sand in reservoirs, irrigation canals and hydropower projects. This is a result of inappropriate land management, such as shifting cultivation and dryland farming, without proper conservation treatment and does not follow land use patterns.

So, to cope with floods, in the upstream area there must be a lot of plants or vegetation because of the position of the upstream area as a buffer zone. This needs to be maintained so that water flows remain (balanced), both in the dry season and in the rainy season. In addition, to maintain the balance of the watershed ecosystem, it must also be considered the problem of waste, both household and industrial waste.

The factors that affect the watershed are climate, the type of rock that the watershed goes through, and a lot of water falls into the groove during rain. Whereas fast or slow rain water collected in a groove is strongly influenced by the shape of the slope of the watershed. Within the watershed area there are natural forms such as meanders, floodplains and deltas.

Calculation of the amount of rain in a watershed can be done using two ways, namely:

1.      Isohyet, used when the watershed area is greater than 5,000 km2. Isohyet is a line in a map that connects places that have the same amount of rainfall in a given period.

2.      Thiessen, used if the watershed is not elongated and narrow, with an area between 1,000 - 5,000 km2.

Isohyet

Object Source: https://www.youtube.com/watch?v=n9eKQQiD86Q

Thiessen

Object Source: https://www.youtube.com/watch?v=ztiBYCMY4PI

The watersheds are divided into three, namely in the upstream area of ​​the river, the middle river area, and the downstream area of ​​the river.

Generally, the watershed in the upper reaches of the river is hilly and steep, so many rapids and waterfalls are found. Upstream river valleys generally resemble the letter V with steep cliffs, because the river flow is still very heavy so that the erosion process erodes into the riverbed. Around the river body there are many large and relatively pointed boulders. This area is widely used for vegetable fields, plantations, or forests which are buffer zones. Around the river there are residential settlements.

The watershed in the middle of the river, the situation is in the form of a relatively flat sloping area so that transportation and communication routes are relatively easy. The sloping area conditions allow the erosion process to take place vertically and laterally in a balanced manner, so that the shape of the valley usually resembles the letter U. Around the river body there are many stones whose surface is relatively round and not as large as upstream rock. Stones whose surfaces are relatively round occur due to polishing by material transported by river water, especially gravel and sand. In the middle area there are rarely found rapids or waterfalls, even none. This area is a place of population activity.

In the downstream area, the watershed is a sloping and fertile area. Therefore, this area is widely used for settlements and agricultural areas (for example rice, corn, and coconut). The area is very flat and approaching the river mouth. River water flows very slowly and many meanders are found. Horseshoe lake (oxbow lake) that is cut off meander flow can be found in the downstream area. The downstream area is a vast flood plain and the shape of the valley is very wide. Downstream there are also many river banks as a result of sedimentation of mud and soft sands.

In Indonesia, there are many disasters related to rivers, such as floods. Floods occur because there is damage to the function of the river. This is a sign that the condition of the Watershed is also problematic. Development that is not in accordance with the environment is the cause, but there is no total problem solving and the integration between parties is not good. According to the KLHK (Ministry of Environment and Forestry) Minister, Siti Nurbaya, once stated that 2,145 Watersheds in Indonesia must be restored. There needs to be strategic and concrete actions from various parties to restore a damaged environment.

Environmental sustainability will benefit all parties. If the Watershed can be restored, it will be able to support the resource needs of both current and future generations.

Wiroko river (one of the upper reaches of Bengawan Solo, the largest river in Java) during the rainy season

Wiroko River during the dry season

Reference:

·         Wardiyatmoko, K. 2004. Geografi SMA Jilid 1 untuk Kelas X Kurikulum 2004 Berbasis Kompetensi. Jakarta: Erlangga.

·         Rahayu, Saptanti and friends. 2009. Nuansa Geografi 1: untuk SMA/MA Kelas X. Jakarta: Pusat Perbukuan Departemen Pendidikan Nasional

·         Utoyo, Bambang. 2009. Geografi 1 Membuka Cakrawala Dunia untuk Kelas X Sekolah Menengah Atas/Madrasah Aliyah. Jakarta: Pusat Perbukuan Departemen Pendidikan Nasional.

·         https://news.detik.com/kolom/d-4436027/integrasi-pengelolaan-daerah-aliran-sungai