DRAINASE SISTEM DRAINASE SISTEM POLDERPOLDER

Wahyu WidiyantoWahyu WidiyantoUnsoedUnsoed

PENGERTIANPENGERTIAN Polder : suatu kawasan atau lahan reklamasi Polder : suatu kawasan atau lahan reklamasi

dengan kondisi awal mempunyai muka air tanah dengan kondisi awal mempunyai muka air tanah tinggi yang diisolasi secara hidrologis dari tinggi yang diisolasi secara hidrologis dari daerah di sekitarnya dan kondisi muka air (air daerah di sekitarnya dan kondisi muka air (air permukaan dan air tanah) dapat dikendalikan. permukaan dan air tanah) dapat dikendalikan. Kondisi lahannya sendiri dibiarkan pada elevasi Kondisi lahannya sendiri dibiarkan pada elevasi asalnya atau sedikit ditinggikan.asalnya atau sedikit ditinggikan.

PolderPolder adalah sebidang tanah yang rendah,  adalah sebidang tanah yang rendah, dikelilingi oleh dikelilingi oleh embankmentembankment / timbunan  / timbunan atau tanggul yang membentuk semacam atau tanggul yang membentuk semacam kesatuan hidrologis buatan, yang berarti tidak kesatuan hidrologis buatan, yang berarti tidak ada kontak dengan air dari daerah luar selain ada kontak dengan air dari daerah luar selain yang dialirkan melalui perangkat manual. yang dialirkan melalui perangkat manual.

SIFAT-SIFAT POLDERSIFAT-SIFAT POLDER Polder merupakan daerah yang dibatasi dengan baik, Polder merupakan daerah yang dibatasi dengan baik,

dimana air yang berasal dari luar kawasan tidak boleh dimana air yang berasal dari luar kawasan tidak boleh masuk, hanya air hujan (dan kadang-kadang air masuk, hanya air hujan (dan kadang-kadang air rembesan) pada kawasan itu sendiri yang dikumpulkan.rembesan) pada kawasan itu sendiri yang dikumpulkan.

Dalam polder tidak ada aliran permukaan bebas seperti Dalam polder tidak ada aliran permukaan bebas seperti pada daerah tangkapan air alamiah, tetapi dilengkapi pada daerah tangkapan air alamiah, tetapi dilengkapi dengan bangunan pengendali pada pembuangannya dengan bangunan pengendali pada pembuangannya (dengan penguras atau pompa) untuk mengendalikan (dengan penguras atau pompa) untuk mengendalikan aliran ke luar.aliran ke luar.

Muka air di dalam polder (air permukaan maupun air Muka air di dalam polder (air permukaan maupun air bawah permukaan) tidak bergantung pada permukaan bawah permukaan) tidak bergantung pada permukaan air di daerah sekitarnya dan dinilai berdasarkan elevasi air di daerah sekitarnya dan dinilai berdasarkan elevasi lahan, sifat-sifat tanah, iklim, dan tanaman.lahan, sifat-sifat tanah, iklim, dan tanaman.

Gambaran Sistem PolderGambaran Sistem Polder

Gambaran Sistem PolderGambaran Sistem Polder

KOMPONEN-KOMPONEN KOMPONEN-KOMPONEN SISTEM POLDERSISTEM POLDER

1.1. Tanggul keliling dan atau pertahanan laut Tanggul keliling dan atau pertahanan laut (sea defense) atau konstruksi isolasi (sea defense) atau konstruksi isolasi lainnyalainnya

2.2. Sistem drainase lapangan (field drainage Sistem drainase lapangan (field drainage system)system)

3.3. Sistem pembawa (conveyance system)Sistem pembawa (conveyance system)4.4. Kolam penampung dan stasiun pompa Kolam penampung dan stasiun pompa

(outfall system)(outfall system)5.5. Badan air penerima (recipient waters)Badan air penerima (recipient waters)

Stasiun pompa

TanggulStasiun pompaRecipient waters

Recipient waters

-2,5

-1,5

-1,25

-1,15

-1,5

ASPEK TEKNIS SISTEM POLDERASPEK TEKNIS SISTEM POLDER

1.1. Pembangunan tanggul lautPembangunan tanggul laut2.2. Penurunan tanahPenurunan tanah3.3. Konservasi pantaiKonservasi pantai4.4. Manajemen polderManajemen polder

Pembangunan Tanggul LautPembangunan Tanggul Laut Tanggul laut dalam sistem polder merupakan Tanggul laut dalam sistem polder merupakan

pembatas hidrologi yang melindungi daerah di pembatas hidrologi yang melindungi daerah di dalam sistem polder dari pengaruh air laut dalam sistem polder dari pengaruh air laut (pasang surut dan gelombang). (pasang surut dan gelombang).

Pembuatan tanggul laut harus memperhatikan Pembuatan tanggul laut harus memperhatikan kondisi tanah setempat. Banyak tanggul laut kondisi tanah setempat. Banyak tanggul laut harus dibuat pada lokasi yang kondisi tanahnya harus dibuat pada lokasi yang kondisi tanahnya sangat lunak, sehingga resiko kegagalan lereng sangat lunak, sehingga resiko kegagalan lereng (slope failure) sering terjadi.(slope failure) sering terjadi.

Penurunan TanahPenurunan Tanah

Banyak sistem polder yang dikembangkan Banyak sistem polder yang dikembangkan di daerah endapan alluvial, dengan kondisi di daerah endapan alluvial, dengan kondisi tanah lunak yang cukup tebal, sehingga tanah lunak yang cukup tebal, sehingga penurunan jangka panjang akibat proses penurunan jangka panjang akibat proses konsolidasi sangat berpengaruh terhadap konsolidasi sangat berpengaruh terhadap elevasi akhir, dan dapat menyebabkan elevasi akhir, dan dapat menyebabkan kerusakan pada bangunan-bangunan.kerusakan pada bangunan-bangunan.

Konservasi PantaiKonservasi Pantai Kawasan pantai merupakan daerah yang Kawasan pantai merupakan daerah yang

sangat potensial untuk dikembangkan.sangat potensial untuk dikembangkan. Keanekaragaman pemanfaatan kawasan Keanekaragaman pemanfaatan kawasan

pantai yang melibatkan berbagai pihak pantai yang melibatkan berbagai pihak dapat menimbulkan konflik dan dapat menimbulkan konflik dan permasalahan bagi pengguna maupun permasalahan bagi pengguna maupun pengambil keputusan.pengambil keputusan.

Perencanaan setiap prasarana harus Perencanaan setiap prasarana harus dilakukan secara terpadu/integral.dilakukan secara terpadu/integral.

Manajemen PolderManajemen Polder Sistem polder merupakan bangunan yang Sistem polder merupakan bangunan yang

beresiko tinggi, sehingga perlu manajemen yang beresiko tinggi, sehingga perlu manajemen yang memadai.memadai.

Manajemen polder yang menyangkut operasi Manajemen polder yang menyangkut operasi dan pemeliharaan, ditujukan untuk mencegah dan pemeliharaan, ditujukan untuk mencegah penurunan fungsi dari semua elemen yang ada penurunan fungsi dari semua elemen yang ada di dalam sistem polder, yang meliputi tanggul, di dalam sistem polder, yang meliputi tanggul, jaringan drainase, kolam tandon, stasiun pompa, jaringan drainase, kolam tandon, stasiun pompa, dan receiving waters.dan receiving waters.

A A polderpolder is a low-lying tract of land enclosed by embankments known as is a low-lying tract of land enclosed by embankments known as dikesdikes, , that forms an artificial that forms an artificial hydrologicalhydrological entity, meaning it has no connection with entity, meaning it has no connection with outside water other than through man operated devices. There are three types of outside water other than through man operated devices. There are three types of polders:polders:

Land reclaimedLand reclaimed from a body of water, such as a from a body of water, such as a lakelake or the or the sea bedsea bed Flood plainsFlood plains separated from the sea or river by a dike separated from the sea or river by a dike MarshesMarshes separated from the surrounding water by a dike and consequently separated from the surrounding water by a dike and consequently

drained. drained. The ground level in drained marshes subsides over time and thus all polders will The ground level in drained marshes subsides over time and thus all polders will

eventually be below the surrounding water level some or all of the time. Water eventually be below the surrounding water level some or all of the time. Water enters the low-lying polder through ground swell due to water pressure on ground enters the low-lying polder through ground swell due to water pressure on ground water or rain fall and transportation of water by rivers and canals. This usually water or rain fall and transportation of water by rivers and canals. This usually means that the polder has an excess of water that needs to be pumped out or means that the polder has an excess of water that needs to be pumped out or drained by opening drained by opening sluicessluices at at low tidelow tide. However, care must be taken in not setting . However, care must be taken in not setting the internal water level too low. Polder land made up of the internal water level too low. Polder land made up of peatpeat (former marshland) (former marshland) will show accelerated compression due to the peat decomposing in dry conditions.will show accelerated compression due to the peat decomposing in dry conditions.

Polders are at risk from flooding at all times and care must be taken to protect the Polders are at risk from flooding at all times and care must be taken to protect the surrounding dikes. Dikes are mostly built using locally available materials and surrounding dikes. Dikes are mostly built using locally available materials and each has its own risk factor: sand is prone to collapse due to oversaturation by each has its own risk factor: sand is prone to collapse due to oversaturation by water while dry peat is lighter than water, making the barrier potentially unstable in water while dry peat is lighter than water, making the barrier potentially unstable in very dry seasons. Some animals dig tunnels in the barrier, undermining the very dry seasons. Some animals dig tunnels in the barrier, undermining the structure; the structure; the muskratmuskrat is notorious for this behavior. For this reason in the is notorious for this behavior. For this reason in the Netherlands it is actively hunted to extinction. No such care is taken in Netherlands it is actively hunted to extinction. No such care is taken in neighboring Germany though, causing the stock to be constantly resupplied neighboring Germany though, causing the stock to be constantly resupplied across the border.across the border.

Polders are most commonly found, though not exclusively so, in river deltas, Polders are most commonly found, though not exclusively so, in river deltas, former former fenfen lands and coastal areas. lands and coastal areas.

Polders and the NetherlandsPolders and the Netherlands The The NetherlandsNetherlands is frequently associated with polders. This is illustrated by the is frequently associated with polders. This is illustrated by the

English saying: English saying: God created the world, but the Dutch created HollandGod created the world, but the Dutch created Holland.. The Dutch have a long history of reclamation of marshes and fenland, resulting in The Dutch have a long history of reclamation of marshes and fenland, resulting in

some 3,000 polders some 3,000 polders [1][1] nationwide. About half of all polder surface within northwest nationwide. About half of all polder surface within northwest Europe is located within the Netherlands. The first embankments in Europe were Europe is located within the Netherlands. The first embankments in Europe were constructed in Roman times. The first polders were constructed in the 11th century. constructed in Roman times. The first polders were constructed in the 11th century. Due to flooding disasters Due to flooding disasters water boardswater boards called called waterschapwaterschap (below sealevel) or (below sealevel) or hoogheemraadschaphoogheemraadschap (above sea level) were set up to maintain the integrity of the (above sea level) were set up to maintain the integrity of the water defenses around polders, maintain the waterways inside a polder and control water defenses around polders, maintain the waterways inside a polder and control the various water levels inside and outside the polder. Water bodies hold separate the various water levels inside and outside the polder. Water bodies hold separate elections, levy taxes and function independently from other government bodies. Their elections, levy taxes and function independently from other government bodies. Their function is basically unchanged through this day. As such they are the oldest function is basically unchanged through this day. As such they are the oldest democratic institution in the country. The necessary co-operation between all ranks in democratic institution in the country. The necessary co-operation between all ranks in maintaining polder integrity also gave its name to the Dutch version of third way maintaining polder integrity also gave its name to the Dutch version of third way politics - the Polder Model.politics - the Polder Model.

The 1953 flood disaster prompted a new approach to the design of dikes and other The 1953 flood disaster prompted a new approach to the design of dikes and other water retaining structures, it is based on an acceptable probability of overflowing. water retaining structures, it is based on an acceptable probability of overflowing. Risk is defined as the product of probability and consequences. The damage in lives, Risk is defined as the product of probability and consequences. The damage in lives, property and rebuilding costs is offset against the cost of water defenses. From these property and rebuilding costs is offset against the cost of water defenses. From these calculations follow an acceptable flood risk from the sea at 1/10,000 years - 1/4,000, calculations follow an acceptable flood risk from the sea at 1/10,000 years - 1/4,000, 1/2,500 years - 1/100 years for a river flood. For comparison the risk of the New 1/2,500 years - 1/100 years for a river flood. For comparison the risk of the New Orleans (repaired) dike system in the future collapsing due to sea flooding is Orleans (repaired) dike system in the future collapsing due to sea flooding is estimated at 1/100 years[2] (i.e. flooding risks in New Orleans remain 100 times estimated at 1/100 years[2] (i.e. flooding risks in New Orleans remain 100 times higher compared to Rotterdam which is set at 1/10,000) The established policy forces higher compared to Rotterdam which is set at 1/10,000) The established policy forces the Dutch government to improve flood defenses as new data on threat levels the Dutch government to improve flood defenses as new data on threat levels becomes available.becomes available.

Polder Tawang, Semarang

1. Tanggul keliling untuk melindungi dari rob

2. Dam untuk membendung sungai. Dam merupakan bagian dari tanggul keliling.

3. Stasiun pompa, untuk mengalirkan air hujan dan menjaga tinggi muka air dalam polder

4. Kolam retensi

Polder Banger, sedang dibangun di Semarang.