The following are the questions I seek to ask as a researcher: 1) how can we improve our understanding of hydrology?, 2) how can we improve our methods of flood inundation mapping and risk assessment?, and 3) how can we leverage existing technologies for hydraulic and hydrologic modeling?
Presently, my research focuses on the Natural Resources Conservation Service (NRCS) Curve Number Method - which is a procedure for determining runoff depths given precipitation. I am involved in the Curve Number Hydrology Committee of the American Society of Civil Engineers (ASCE). My current research revolves around investigating the effect of duration on curve number estimates. Previously, I co-authored a paper on establishing a rationale for choosing the appropriate initial abstraction ratio. In the past, the debate has been mostly binary - either choose 0.05 or 0.2; however, this contribution provided conservatism, as a defensible, and objective criterion with which to choose the value of the initial abstraction ratio.
My work as a PhD student at Texas A&M University involved developing a new approach for determining the peak discharge of a storm hydrograph (graph of flow with time) for Texas. This work was part of, and partially funded by, a Texas Department of Transportation (TxDOT) project “Peak Rate Factor Estimation for Hydrological Modeling”. The peak rate factor (PRF) is a parameter in the NRCS Unit Hydrograph method. The PRF was derived to be 484; however, the initial study that suggested this value (Mockus, 1957) was conducted considering watersheds in the Midwest United States. Part of my research aimed to investigate this value for Texas watersheds. Results showed that PRF is less than 484 for Texas watersheds, and PRFs in Houston are even lesser, which means that the hydrographs for Texas – and especially in Houston – are more front-loaded than the shape of the recommended NRCS hydrograph. This result would be significant in reducing overdesigned infrastructures and thereby saving millions of dollars in infrastructure development.
In the past, I have also been involved in other hydrological studies. For my master’s work at The University of Texas at Austin, I developed a new method for determining flow directions and flow accumulations in an urban area. Knowing where water flows and accumulates is important in flood mapping; however, most methods in determining these parameters uses a static elevation model. Flow directions, however, may be complicated in urban areas. Using a small area in Austin, I used a hydraulic model to simulate the flow and from the model results, process datasets on flow directions and flow accumulations. The most significant finding in this research is that while the general direction of flow is from a higher elevation to a lower elevation, the localized flow can be in all directions. This finding permits continued application of flood inundation mapping using static elevation models but at the same time encourages the use of hydraulic models in determining more accurate flow directions and accumulation, and therefore, more reliable flood maps.
For my undergraduate thesis which I did at the University of the Philippines Los Banos (UPLB), I investigated on the compressive strength of concrete hollow blocks with polypropylene pellets as partial replacement for sand. This study was motivated by plastics being non-biodegradable, which creates a problem of disposal. In the Philippines, this problem is exacerbated because of lack of sanitary landfills. In this study, polypropylene (PP), which is a subset of these plastics, were pelletized and incorporated in concrete hollow blocks as partial replacement for sand. Tests such as determination of the specific gravity of the materials, and sieve analysis and fineness modulus of the aggregates were performed before molding. Five batches of specimens, each with 0%, 10%, 20%, 30%, 40% PP replacement (by volume) were molded and cured for 28 days. The compressive strength and bulk density of the specimens from these batches were determined and compared. Results showed that, generally, compressive strength and bulk density decrease as percent replacement increases; however, an exception to the trend was observed in that the compressive strength of the specimens from the batch with 10% PP replacement were higher than that of the specimens from the batch with 0% PP replacement. It was concluded that PP pellets, up to 10% replacement, has potential as partial replacement for sand, provided that financial constraints are satisfied. This research has also become my resource for advising undergraduate students at UPLB.
Finally, I have also conducted a number of isolated research studies. One of this is the application of the Height Above Nearest Drainage (HAND) flood mapping methodology on the Philippines. In this effort, I showed that using free online data sources, and a GIS software, one can produce an approximate terrain-based flood map for a large region such as the Philippines.
