By: Edgar Mana-ay
FIRSTLY we welcome all delegates from different countries on this historic International River Summit that will be held for the first time in Iloilo City. This indeed is recognition of the effort of Mayor Mabilog administration to place environmental protection as his priority program.
This writer looks at rivers and streams as a human being. Just like the baggage man at the pier or the cargador in a public market, the river carries the load (both sediments and water) that the watershed imposes on it to deliver towards the seas. A businessman can force its cargador to carry two sacks of rice which the cargador will meekly follow but will throw it when unloading causing the sacks to burst. Just like a human being, rivers react to the load given by the watershed. Within reasonable limits, it can adjust its width, depth and meander if there is an increase in its load. If imposed with load beyond its equilibrium capacity and its physical landscape ERRONEOUSLY revised by man in the name of progress, the river fights back by destroying its banks and overflows to the plains. The recent devastating flood during Typhoon Frank showed how an abused river can vent its ire to the populace. To quote Skylock in the play The Merchant of Venice by Shakespeare, a river would say, “If you wrong us, shall we not revenge?”
Like a growing child, there is a need to “baby” the river. Controlling, restoring and maintaining rivers and streams AT GRADE requires a soft approach without dependence on steel and concrete which is the hard approach of the Japanese, blitzkrieg style, reminiscent of the “shock and awe” U.S. invasion of Iraq. We have to ENHANCE the natural tendencies of rivers to adjust ITSELF in order to seek a quasi-equilibrium between its sediments and water load both at low flow and in flood to return to a river at grade or at equilibrium. The hydraulic variables involve which we have to consider are: the volume and timing of the water load from the watershed, the sediments the water load is carrying and the flow velocity. Then the geometric variables which a river will have to self adjust are: width/depth ratio, gradient, sinuosity and meander geometry.
The pressure of development and the desire of the present society for profits at the expense of anything natural ,wild or free has degraded and abused the landscape of rivers throughout the world by river engineering, river straightening, construction of levees, dams and concrete channel as in the 4 km. man made straight Jica floodway. This has resulted in numerous river bank erosions upstream of the Jica Project in Pavia and Sta. Barbara, endangering bridges and homes along the rivers because of increased water velocity which this writer predicted as early as October 6, 2008 (Bare Facts column of this writer with The Daily Guardian) when the Jica flood control project was just starting. There is therefore the need to shift from the Hard to the Soft approach in river restoration. In the U.S., Dave Rosgen, an expert in Fluvial Geo Morphology or FGM (the land mass that a river affects, influence and form), uses the Soft Approach in river restoration, control and maintenance. This approach uses native materials such as stones, boulders, fallen trees or even used tires applied in ways that enhances the natural tendencies of rivers to be a river at grade or at equilibrium.
In dealing with rivers, never shall we forget the WEATERSHED. It is basic hydro-geology concept that rivers and watersheds are the SIAMESE TWINS of flooding and erosion. If BOTH are sick as in the case of Tigum and Aganan rivers and its corresponding watersheds which is the primary cause of flooding in Metro Iloilo, then healing one twin will not solve the flooding and erosion problem but will only aggravate the conditions of both.
Fifteen years ago, a foreign consultant made a study of the Tigum and Aganan watershed comparing it with what it was a hundred years ago from date of study. Result of that study shows: In 1997, 37 percent of total rainfall flows to the Tigum and Aganan rivers, it was only 20 percent a hundred years ago. Due to reduced forest cover, effective rainfall increased to 46 percent from 32 percent a hundred years ago. Recharge of underground water resource was also reduced from 12 percent to only 8.5 percent. These are disheartening figures showing tremendous load increase to our river system and since 1997, the time of the study, NO improvements was made on the Tigum and Aganan watersheds. We have to understand and identify the processes in the watershed that causes flooding or dis-equilibrium of its river system and effect a healing process.
Norman Maclean (1976) has this to say about rivers: “Eventually, all things merge into one, and a river runs through it. The river was cut by the world’s great flood and runs over rocks from the basement of time. It sings a song of wisdom and life far greater than man can hear.”