[To help readers understand the problem of flooding in Cotabato City and its environs, MindaNews reprints this situation report as of June 17, 2011 prepared by Nathaniel A. Campo, Deputy Executive Director of the Presidential Task Force for the Mindanao River Basin Rehabilitation and Development (PTFMRBRD) Support Office, and chair of the Mindanao River Integrated Management and Development Master Plan (MRBIMDMP) Technical Working Group. With notes from Archbishop Orlando B. Quevedo, chair of the PTFMRBRD]
Background
|
The flooding in the City of Cotabato primarily is a result of the heavy rains that started last May 22, 2011 and continue to fall almost simultaneously in the entire Mindanao River Basin. While the volume of rainwater that fell is just above the normal range of the highest recorded rainfall during the wet season, the abnormality is that the rains fell at almost the same time – in all the areas of the river basin. The two major rivers at all its tributaries coming from headwaters located in Bukidnon, Agusan Sur, Davao Norte, Davao City, South Cotabato and Maguindanao all flow into one catchment lake – the Ligawasan Marsh.
The Ligawasan marsh is composed of three separate marshes, Ligawasan, Libungan and Ebpanan. These marshes defined only during the dry season combines as the entire Ligawasan marsh during the rainy season. The Ligawasan and Libungan marshes empty into the Ebpanan marsh which in turn flows into the Rio Grande de Mindanao whose only two outlets are in Cotabato City.
The continuous simultaneous rain aggravated by emergency releases of water from the NAPOCOR, PULANGUI IV (totally around 98million cubic meters in 20 days) immediately caused the level of the said marsh to rise and as the water rose, it uprooted the water hyacinths that have over the years proliferated in the said marshes. With the swelling of the river mouths and increase in current, huge volumes of said plants began break away and slowly drifted to Cotabato City.
The current water hyacinth clog at the Delta Bridge in Cotabato City was a build-up that occurred in just two days. Given that the three marshes has over 80 thousand hectares of water hyacinth, it is expected that more of these plants will be flowing into the city rivers over the next few weeks. An aerial survey conducted by the Task Force last June 11, 2011 showed that about 20 hectares of water lilies are moving slowly into the city.
Causes, Effects, Action Taken and Recommendations
The Clog at Delta Bridge
The mass of water hyacinth is estimated to be about 10 to 12 hectares as of June 14, 2011. This mass has already hardened and reached the river bed which is estimated to be about three to four meters deep. The said clog has already formed as a natural dam and caused a major portion of the water to overflow into the Matampay River in the right and to Barangay Bulibod, Sultan Kudarat Municipality on the left. While the effects at Barangay Bulibod is relatively small as it is sloped upwards, the water run-off towards the Matampay river is causing havoc to the low lying barangays of Cotabato City. With the Matampay river itself already swollen, the overflow from the Rio Grande has nowhere to go but the city.
To date, 30 of the 37 barangays of the city have been inundated at various levels, the deepest of which was measured to be about 1.6 meters. This was recorded in areas near the riverbank.
While several means can be used to declog the massive accumulation of water lilies, the efforts are hindered by the fact that most of the land based equipment are ineffective as the mass is located in the middle of the river and beyond the reach of said equipment. Therefore, initially only the two WaterMasters (dredging machines) were able to work in this condition.
Eventually, concerted efforts of various government agencies, LGUs (local government units) with the assistance of the AFP (Armed Forces of the Philippines), focused on opening channels along the sides of the river to redirect a major portion of the river flow to its original course. These side channels were made with great effort and completed by evening of June 16. They served as a way to push the arriving water lilies to allow them to flow freely and avoid further accumulation.
However, more water hyacinth arrived during the night. Worse, the whole mass of water hyacinth moved and covered the river edge near Salimbao. The morning, therefore, of June 17 was devoted to clearing this side of the river. Once again, the flow of water hyacinth towards the sea was unobstructed. However, we also believe that imperative to slowly remove the upper portion of the mass is to use a crane to allow the water lilies to float. Doing so would allow water to flow under the lilies and increase the water flow. This will allow the easy break-up of the water lilies while at the same time allowing more water volume into the Rio Grande which in turn reduces the overflow of the water into the Matampay River. Without water from the Rio Grande, most of the waters in the city will eventually flow back to the Matampay River.
The Siltation of Rio Grande
The second issue that needs to be addressed immediately is the heavy siltation of the Rio Grande. While several dredging activities are being conducted, the effects of these projects are so small that unless done in a super massive scale, the dredged silt are easily replaced by new silt coming from upstream. This brings to fore the need to be able to control siltation from upstream.
The silt coming from the Ambal-Simuay River system is the main culprit for the heavy siltation of the Rio Grande. The Ambal Simuay River is similarly silted that after Typhoons Frank and Cosme in 2008, the river has discoursed permanently towards the populated barangays of Bulalo and Salimbao and in many occasions caused the inundation of the national highway linking Cotabato to Davao City.
While a cut-off channel was earlier constructed to redirect a portion of the flow of the water, the channel in itself does not arrest the flow of silt. Further, the design of the channel has to be reviewed and several changes need to be made to make it more effective.
Among the more immediate dangers that have been identified is the current sandbar that has formed at the Katuli junction where the Matampay and the Rio Grande joins. This sandbar is massive and it is feared that as soon as the water flow of the Rio Grande is returned, this sandbar may be pushed into the Matampay river path causing it to form as a natural dam and further cause the water level of Matampay river level to rise.
Down the channel of the entire Rio Grande, several sandbars have been detected and some have been addressed by the dredgers. However, unless and until the siltation feed from the Simuay river is reduced, these dredging activities will be a continuous battle just to stay ahead.
The Ala River
The Ala River System is one of the main culprits in the heavy siltation in the Libungan Marsh. The denuded forests of the Daguma mountain range, the fast current from Lake Maughan and the loose soil from agricultural lands of South Cotabato and Sultan Kudarat provinces are the primary sources of silt of the river.
The heavy siltation of the Ala river is the primary cause of the meandering of the river and creating new river pathways during heavy rains. As evidenced by pictures taken during the aerial survey conducted by the Task Force, the river has breached its banks along its routes and inundated several thousands of rice and corn farms.
In 2008, at the height of Typhoons Frank and Cosme, the town of Lambayong, Sultan Kudarat was flooded when the river breached its banks at Barangay Sadsalan. Over 5,000 hectares of farmlands were damaged during the inundation. The DPWH in response constructed a dike that covered the breach and eventually caused the river to return to its original path.
On the first week of June 2011, caused by the siltation that settled about one kilometer from the dikes, the river again discoursed about 500 meters from the end of the dike. This breach caused the flooding of about 2,000 hectares of farmlands and flooded a four-kilometer stretch of the Dulawan-Marbel National Highway.||| |||buy buspar online with |||
By June 7, 2011, the DPWH District Office at Isulan, Sultan Kudarat reported that 100 percent of the river was flowing through the breach.
In a meeting that was called by the Governor of the province, the Task Force and the DPWH District Office presented options to the LGU. After a series of discussions, the LGU decided to use the allotted project fund, which was supposed to construct a dike along the breached portion, to dig a channel to connect the river to the existing channel at Sultan sa Barongis.
While this action was considered as the most expeditious way to resolve the issue, the Task Force made clear that several repercussions may result from such action. Among those immediately identified are: (a) the action does not address the siltation which will continue and eventually reach the dike project and wash it out, further flooding may ultimately reach the town proper of Lambayong; (b) the river is the source of the communal irrigation of some farms at Esperanza, Sultan Kudarat. By staying with the changed course of the river, the farms dependent on the river will not have the water needed for their farm lands.
The provincial government also reiterated their request to the DPWH to re-assign one of the dredging machines to the area to be able to dredge the portion of the river to allow the river to return to its original path.
Located in the heart of Central Mindanao, the Tunggol cut-off channel was constructed several decades ago to divert a portion of the water flow of the Lower Pulangi River directly to the Ligawasan Marsh so as to avoid the flooding of Pikit, Cotabato that often happened after heavy rains. The channel constructed on clay-loam soil eventually widened from its original 40-meter width to its current 120 meter span.
The heavy siltation of the river and the heavy rains have caused the channel to breach in several portions and the upper portion of the channel has formed into a lake. Pictures taken during the aerial survey showed that the channel has transformed into a lake.
The immediate danger is the possible wash-out of the said bridge which is slowly being encircled by creeks on both sides of the bridge.||| |||buy spiriva inhaler online with |||
