By Engr. Edgar Mana-ay
In 1935, the American Forest journal ran an advertisement for Dupont, one of the earliest companies in the world to manufacture dynamite. The ad ran like this: “Crooked streams are a menace to life and crops in the areas bordering their banks. The twisting and turning of the channel retards the flow and reduces the capacity of the stream to handle large volume of water. Floods result. Crops are ruined. Lives are lost . . . take the kinks out of crooked streams . . . Dupont Dynamite has straightened many thousands of miles of crooked streams . . .”
That was 85 years ago when the Americans were as innocent as a new born babe when it comes to fluvial geo morphology (FGM), the landscape that a river forms and influences. At that time they did not know that sinuosity or the winding of river path was provided by nature to control the speed of water flow from the mountains towards the plain because excess water energy is wasted against the bends and curves of river banks. Common sense dictates that a slow river water flow is certainly less destructive than a fast river water flow. Straighten a river and river flow automatically increase. Today the Americans as exemplified by hydro-geologists and river scientists Luna B. Leopold and Dave Rosgen are the world’s experts on how to assess, then restore rivers to its equilibrium capacity making it a river at grade, so that it will not be destructive to man during flood season.
On October 6, 2008 when the Jica Flood Control Project was in the construction stage, I wrote a column in Daily Guardian titled: “Reservations and Misgivings on the JICA Iloilo Flood Control Project”, which I now quote: “Beyond its equilibrium capacity, the river will fight back by destroying its banks and overflow to the plains. If its end portion is STRAIGHT and CONCRETIZED as in the Jica Flood Control Project in Iloilo City, then it will vent its ire UPSTREAM in Pavia, San Miguel, Sta. Barbara and Cabatuan.”
Very true enough, when the Jica Floodway was operational in 2010, river surface water flow DOUBLED in speed during floods, creating a siphon-effect upstream which has caused tremendous riverbank erosion upstream on the not cemented bank portions.
Aside from upstream river bank erosion, other environmental havoc and destructions that the straight floodway caused during floods are: removed river bed sand exposing the river bed basement rock. At Jibaoan, Sta. Barbara portion of Aganan river, old folks told this writer that the excessive water speed removed all the TEN FEET riverbed sand, thus exposing the concrete foundation of the Jibaoan bridge which the DPWH had to repair four years ago.
The high speed water of main Tigum and Aganan rivers also caused siphon/domino effects on the small streams and creeks that feed the main river, leading to massive erosion as in Maliao creek and that unnamed creek in Tigum connecting to the Tigum river.
Our very diligent and industrious congressmen of the second district – from the late father Cong Cads to the present son Cong Mike – have been providing the budget to concretize the eroded banks, sigue lagas pa concrete nga pakadto na subong sa Sta. Barbara. Kon lagson mo lang ang pag pa concrete basi abot ka sa Maasin head waters for both rivers!
This is where DPWH will have to apply science in solving the river bank erosion upstream of the concreted Jica Flood Control Project, which is really HOW TO REDUCE SPEED OF RIVER WATERS DURING FLOODS CAUSED BY THE STRAIGHT FLOODWAY. Unfortunately, they have remain a greenhorn just like the Americans 85 years ago in addressing the serious geo-morphology problem brought about by the Jica straight floodway. They would rather stick to the Hard Approach of the Japanese “structure mania”, the steel and concrete approach, which is not only expensive but contrary to the river’s central tendency for self-stabilization. This overkill approach is often referred to as “getting nibbled to death by a duck”. There is a German term that often applies to such designs –schlimmbesserung – meaning, the so-called improvements that makes things worse!
Nature (the rivers) has its own way of healing itself even if man has mangle and disfigure it (the straight floodway and massive bank concreting) in the name of progress and flood control. Rivers are created by nature that it has its own way of adjusting itself to the water and sediment load from the watershed but only up to a certain limit. Look at the straight floodway and the concreted upper reaches of Tigum and Aganan rivers. Left alone in the past five years, the channel has:
A. Narrowed itself due to accretion or buildup of geologic materials (soil, sand and gravel); and
B. Cogon grasses up to 8 ft. tall to provide flow resistance have grown on the piled-up sediment.
This is NATURE’S WAY OF ADJUSTING ITSELF so it can reduce the speed of its water flow during flood. But nature can only do so much, for beyond that limit and especially if the river is NOT at grade or at equilibrium, the river becomes destructive upstream of the Jica straight floodway and man has to assist in restoring the rivers.
Fluvial Geo Morphology (FGM) science should therefore be applied in the removal of accumulated soil in the straight floodway – meaning there must be a scientific way of doing it. As it is now, it is money, money and money that is the governing factor so that the aim is TOTAL REMOVAL TO RETURN IT TO ITS ORIGINAL BARE FLOODWAY. Then again we return to the original HIGH SPEED river water flow which will again cause bank erosion upstream of Tigum and Aganan rivers.
As I have stated in my previous article, the Watershed and River are the Siamese Twin of flooding, so let us also not forget the healing of the watershed. We quote Luna B. Leopold (1994), the father of river restoration in the U.S.: “THE RIVER IS THE CARPENTER OF ITS OWN EDIFICE.”
Note: The writer is a professional member of the American Water Works Association (AWWA) and Chairman of the Municipal Water Board and Hydro-geology Consultant during the term of then Pavia Mayor now 2nd district Rep. Mike Gorriceta.
