By John Emmanuel Kawatt


Those living on the Sepik River at Angoram (downstream from Kanduanum) must by now know that the dynamics of the Lower Sepik River has changed. We now see sand bank formation in middle of where once the river was very deep and the constant flooding (up to 3 times in a year) of low-lying areas at Grass Country, Service Camp, Magendo, Angoram, Imbando, Marienberg and Murik Lakes (refer to Figure).


It is understood that the Grass Country region is now submerged almost the entire year-round.


One must surely pause to ask why that is so; I have therefore tried to provide an explanation on the natural mechanics play causing the Sepik to behave the way it presently is. The impacted area of Sepik in Angoram District is highlighted in the above figure.


 The lower Sepik is disadvantaged by its physical setting. The surface of the water at Moim Village (140kms upstream from river mouth) is only 1m (ASL) above sea level at the Sepik River Mouth.
 The gradient for the Sepik to flow from Moim to the sea therefore is  (1m/ 140,000m) which is an exceptionally low gradient at 0.000714. For comparison civil engineers design roads surfaces to have a minimum gradient of 2% to encourage surface drainage of rainwater from road surfaces during rainfall events.


 There is lots of storage capacity for the Sepik water (if it backs up) at its lower Sepik end at Wangan, Imbundo & Kambaramba Lagoons, the Grass Country, and Lakes at Tambari and Penang. The Sepik itself would swell hence Service camp and other low-lying areas would also get flooded.


 Sea water is denser (or heavier) than fresh Sepik River Water. Salt water has a density of 1.025t/m3, compared to 1.00t/m3 for fresh river water.


That also means that your fully laden “banana boat” would float better is saltwater than in fresh water hence you’d use less fuel for identical distances travelled in saltwater than in fresh water.
And so, when we get King Tides (high tides) in the Bismarck Sea, the sea level at Kopar would rise further reducing the flow gradient, from Moim to Kopar cited above.
Also, fresh river water is light weight compared to  the denser saltwater (i.e., 1.00t/m3 – compared to 1.025t/m3). So, when the Sepik meet the Ocean,  it backs up, its velocity (or flow rate) reduces to zero??

When that happens the sediment load ( silt and sand transported in suspension) sinks to the river bottom, and we get delta formation at areas where a very deep Sepik once flowed all the way up to Moim Village.


If the sea level was to rise by 1m than we could get mangrove swamp development all the way up to Moim. We would lose all our freshwater lakes and lagoons and our sago swamps would also diminish and disappear.


Angoram – We need a plan of action going forward. We are already seeing our Murik folks migrating into Wewak in droves. I am told that the Murik Compound at Wewak has swelled na niupla Karau, Mendam, Darapap now kamap stap long Wewak? I stand to be corrected here please.