Phnom Penh/ Why is water-land relationship delicate?
We’ve been saying that Phnom Penh is a city susceptible to flooding. This is largely due to it being located in a low-lying region surrounded by various water bodies, but that is not the only reason. Sure, rainwater increases during the rain season, but this is coupled with abnormally heavy water runoff from the melting of snow in Tibet. Exceptionally heavy rains in the mountains of Szechwan, upper Laos, and the Annamite mountain chain could also cause a drastic change in water flow causing floods in the entire Mekong Valley. If the waters surpass 12m above sea level, the city will be easily submerged in water (note: Phnom Penh has an elevation ranging from 7-14m above sea level depending on which areas of the city one is looking at). So yes, this makes it hard for the city’s water flow to reach an equilibrium, but what’s more that makes such a water-land relationship so delicate?
This can perhaps be reasoned back to the natural land and land use in the city. Floodwaters along the Mekong and Bassac Rivers, as well as long the Tonle Sap and Tauch Rivers, has brought deposits of gravel and sand along with other elements that result in several types of soils:
On the river banks, an alluvial sandy soil is formed especially along “prek” or canals, and at where the “prek” run into the “beng”. Such kind of soil is slightly alkaline, very light, and susceptible to humidity. Water can rise through it by capillary action even during dry season, benefiting trees along the banks all year long.
Where water runs slowly with very little current are water bodies that are the best and richest alluvial soil. These deposits are found along riverbanks that slope away from the river and in some low-lying fields adjacent to these banks. This type of soil has less percentage of gravel and sand compared to the soil mentioned above, and its component consists of more clay. They are also very often accumulated to great depths. This homogeneous and thick soil allows for good water circulation and can also conduct water during the dry season through capillary action.
Behind riverbanks are plains covered with clay-filled soil that is more compact. This type of soil is found only in plains of low-lying areas, and emerge gradually after floods. Areas as such are hard to cultivate during the dry season unless intensive irrigation is involved.
The fertile land along the banks and the plains behind them are prone to annual flooding which renew these areas with silt. Exploitation of land along the Mekong River thus has to be very careful, or the delicate equilibrium between land and water would be destroyed otherwise. Villagers have been adapting to different types of soil cleverly in their cultivation – the top of banks where flooding is least likely were for establishment of villages and orchards, whereas slightly less elevated grounds were for cultivation of perennials and plants that require long term cultivation. Capillary action of soil plays an important role here as it is the means of drawing receding flood waters to soil.
According to statistics, Cambodia is populous but not in each and every corner. People tend to reside near rivers, and this is likely to have to do with the soil types and cultivation they provide. Plateaus are sparsely populated, and forests and areas of alluvial silting have almost no population. Water bodies may cause flooding – but floods can be there for good. Floods are productive in cultivation if they are made use of in a smart manner, and this is likely to account for the people residing around riverbanks even though they may face serious floods at times.
The relationship between water and land is therefore important as it leads to the emergence of different soil types – and Khmer people depend on such soil for living. Any interference in the water flow would interrupt not just the space for living but also land for cultivating. Any modifications in the pre-existing water network to make way for urban development therefore requires a meticulously worked out master plan that could match up with the intricate system.