Reconstructing the Tropical Storm Ketsana flood event in Marikina River, Philippines

Abstract

Abstract. In September 2009, Tropical Storm Ketsana (local name: TS Ondoy) hit the Manila metropolitan area (Metro Manila) and brought an anomalous volume of rain that exceeded the Philippines' forty-year meteorological record. The storm caused exceptionally high and extensive flooding. Part of this study was a survey conducted along the stretch of the Marikina River, one of the major rivers that flooded. Postevent resident interviews were used to reconstruct the flooding in the absence of stream gauge data. Hydraulic and hydrologic modeling were carried out to understand the mechanism that brought the flood. Peak floods occurred at different hours along the river resulting from the transmission of water from the main watershed to the downstream areas. Modeled peak flood and flood timing coincided well with actual observations except for downstream stations where actual peak floods were observed to have occurred at a later time. Compounding factors such as other flood sources and stream backflow could have caused this discrepancy. Nevertheless, prediction of flood heights and the use of the known time lag between the peak rainfall and the peak runoff could be utilized to issue timely flood forecasts to allow people to prepare for future flooding.

SCS-CN parameter determination using rainfall-runoff data in heterogeneous watersheds – the two-CN system approach

“…Simple methods for predicting runoff from watersheds are particularly important in hydrologic engineering and hydrological modelling and they are used in many hydrologic applications, such as flood design and water balance calculation models (Abon et al, 2011;Steenhuis et al, 1995;van Dijk, 2010). The Soil Conservation Service Curve Number (SCS-CN) method was originally developed by the SCS (US Department of Agriculture), to predict direct runoff volumes for given rainfall events and it is documented in the National Engineering Handbook, Sect.…”

Landslide-amplified flash floods—The June 2008 Panay Island flooding, Philippines

“…There are unpublished reports of flash floods associated with short-lived landslide dams, such as the 1991 Ormoc and the 2004 Quezon-Aurora flash floods. While the 2009 Ketsana floods that severely affected Metro Manila and adjacent provinces were mainly attributed to extreme rainfall (348 mm in 6 h) (Abon et al, 2011), some areas experienced flash floods due to breaching of landslide dams (unpublished data by authors). However, the contribution of the damming to these flood events has not been quantified.…”

Volcanoes magnify Metro Manila's southwest monsoon rains and lethal floods

“…To the east of Metro Manila is the Marikina River Basin (582 km 2 ) (Abon et al, 2011), which drains into a highly urbanized portion of the metropolis. The Marikina River joins the Pasig River, and drains directly toward Manila Bay and Laguna de Bay.…”

“…The one day maximum rains during the Habagat 2012 and 2013 are near the daily maximum rains of the fatal Tropical storm Ketsana (448.5 mm) (Lagmay et al, 2010;Abon et al, 2011) and Hurricane Katrina (417 mm) (Knabb et al, 2005;Roth, 2008) events, which devastated Metro Manila and New Orleans, respectively. While Tropical storm Ketsana and Hurricane Katrina are both cyclone events, Habagat 2012 and 2013 are simply enchanced monsoon events, and as such, no typhoon warnings were raised.…”