River degradation leads to huge economic and financial losses. It also makes traditional river activities no longer possible, increases risk to flooding, and reduces land value along the river.
Everyone knows that rivers must be preserved or, if need be, rehabilitated. Yet rivers continue to flounder. Is it a lack of legislation, enforcement, awareness and education, leadership or a combination of all these?
Rivers are surface waters receiving all discharges from runoff, wastewater, and even solid waste. As with other water bodies, they have a self-cleaning capacity that can be measured and quantified. In Western countries, this is used to define the effluent discharge standards and the maximum admissible pollution load in a river catchment, which indicates the level of treatment needed. Pollution - from both point and non-point sources - damages rivers by reducing their self-cleaning capacity.
Why rivers get dirty
Rapid urbanization sparks the first phase of river pollution. The increased density of population and more intensive agricultural activities raise the total pollution load of the river well above its self-cleaning capacity. In addition, the drive to increase local economic development usually results in factories peppering the riverside and discharging non-biodegradable pollutants in the rivers. With such pressures from various sources, rivers cannot cope any longer and a slow degradation process begins, one that is very expensive to reverse.
The sediments, measured as suspended solids in the wastewater, settle at the bottom of the river and slowly change the ecosystem within the river. Bacteria and micro-organisms that live at the bottom of the river either die or adapt through a change in metabolism - from aerobic (uses oxygen and discharge carbon dioxide to metabolize pollution) to anaerobic (in absence of oxygen, converts pollution to methane).
Increased biodegradable pollution loads, measured as biochemical oxygen demand or BOD, takes away the oxygen that's naturally available from the river and also changes the river's ecosystem. Finally, when very little or no more oxygen is left because of the accumulation of pollution or discharge of toxins, all the fauna and flora from the river eventually die. The dead flora and fauna accumulate at the bottom of the river, generating foul smell and a typical black color indicative of anaerobic activities. The accumulation of sediments has another side effect - the reduction of the river's volumetric capacity, which results in more frequent flooding.
Tough decision-making
Procedures in cleaning up a river are almost formulaic. However, some crucial steps are either ignored or forgotten, leading to significant cost overruns and delays. In a nutshell, river cleanups should involve the following:
- Prioritize which river section to clean-up; priority should be from upstream to downstream.
- Identify and intercept all discharges points to the river through a comprehensive sewerage and drainage project.
- Conduct a specific environmental impact assessment to remove and to dispose of the sediments. The level of treatment of the sediments will depend on its physico-chemical characteristics. An appropriate discharge site needs to be identified (existing or new landfill), with possible valorization of the sediments for construction.
- Remove the sediments.
After the river cleanup, the river banks would have become very expensive assets. It is now major decision time for the decision-maker. Which direction should the redevelopment of the river lean towards? Should it focus on:
- recalibration of the river to increase flood conveyance;
- construction of wetlands along the river;
- beautification of the river banks, through public parks, foot and bicycle paths, and more high residential development, which maximizes the increased land value commercial development;
- improved transportation, through scenic road along the river or connecting nearby villages;
- ... or a combination of different options?
Undoubtedly, each of these options would have their benefits. But they will also have their trade-offs, often with economic gains and environmental progress at opposing ends of the continuum. Which one should the community or country favor?
Deciding between options may be tough, but it is always good to remember that there have been cases of river cleanup that combined many of these options and came up winners - Marikina River in the Philippines, Suzhou Creek in the People's Republic of China, Singapore River in Singapore and many more.
River cleanups are always an expensive proposition and rivers take a very long time to recover. While economic analyses may demonstrate the economic benefits of river cleanups, at the end of the day, it is still prevention - through advocacy and awareness campaigns - that will save communities lots of money and efforts.
