Monthly Archives: November 2014

The development of a hydrological model for water level forecasting in the Philippines’ deepest lake.

By Arthur M. Amora, Jojene R. Santillan, Meriam M. Santillan

ABSTRACT:

Lake Mainit is considered to be the Philippine’s deepest lake with a maximum depth reaching about 223 m. It is geographically located between the Provinces of Surigao del Norte and Agusan del Norte, in the Island of Mindanao. With a surface area of 149.86 km2, it ranks fourth to Laguna Lake as one of the Philippine’s largest lakes. The lake receives inflows from several major and minor tributaries located in the municipalities of Mainit and Alegria (Surigao del Norte) and Kitcharao and Jabonga (Agusan del Norte). During heavy rainfall events, inflows from these tributaries increase the lake’s water level and causes flooding of barangays located near the shore. This scenario is exemplified recently during the January 2014 Typhoon Agaton. In this paper, we present the development of a hydrologic model of Lake Mainit in order to gain a better understanding of how the various tributaries contribute to the lake’s water level during rainfall events. With the development of this model, the water level in the lake can be simulated or forecasted given the amount of rainfall measured by existing rainfall stations located in the lake’s vicinity.

KEYWORDS: Lake Mainit, reservoir, water level, forecasting, HEC HMS


Publication Details/Metadata:

Paper Title: THE DEVELOPMENT OF A HYDROLOGIC MODEL FOR WATER LEVEL FORECASTING INT THE PHILIPPINES’ DEEPEST LAKE

Authors: Arthur M. Amora, Jojene R. Santillan, Meriam M. Santillan

Publication Date: 2015

Conference Name/Journal/Book Title: 3rd Philippine Geomatics Symposium 2014 (PhilGEOS 2014)

Publisher: Training Center for Applied Geodesy and Photogrammetry, University of the Philippines, Diliman, Quezon City

Link to Full Text: View/Download


 

The development of a hydrological model for water level forecasting in the Philippines’ deepest lake

By Arthur M. Amora, Jojene R. Santillan, Meriam M. Santillan Phil-LIDAR 1.2.14 Project, Caraga Center for Remote Sensing and GIS, College of Engineering and Information Technology, Caraga State University, Ampayon, Butuan City 8600

Background

lake_mainit_map

Figure 1. Map of Lake Mainit

Lake Mainit is considered to be the Philippine’s deepest lake with a maximum depth reaching about 223 m (Lewis Jr., 1973). It is geographically located between the Provinces of Surigao del Norte and Agusan del Norte, in the Island of Mindanao. With a surface area of 149.86 km2, it ranks fourth to Laguna Lake as one of the Philippine’s largest lakes (Tumanda et al., 2003). The lake receives inflows from several major and minor tributaries located in the municipalities of Mainit and Alegria (Surigaodel Norte) and Kitcharao and Jabonga (Agusan del Norte). During heavy rainfall events,inflows from these tributaries increase the lake’s water level and causes flooding of barangays located near the shore. This scenario is exemplified recently during the January 2014 Typhoon Agaton. In this technical report, we present the development of a hydrologic model of Lake Mainit in order to gain a better understanding of how the various tributaries contribute to Lake Mainit’s water level during rainfall events. With the development of this model, the water level in the lake can be simulated or forecasted given the amount of rainfall measured by existing rainfall stations located in the lake’s vicinity.

lake_mainit_3d

Figure 2. Lake Mainit in 3D.

Model Development

We combined various geomatics technologies (remote sensing, GIS, and numerical modeling) in developing the hydrologic model of Lake Mainit. A 10-m Synthetic Aperture Radar – Digital Elevation Model (SAR-DEM),and rivers and stream networks digitized from high resolution satellite images were utilized and processed in HEC-GeoHMS to delineate the sub-basin boundaries and the reach elements of the model. The land cover parameters derived from the analysis of year 2014 Landsat 8 OLI images, and the river roughness characteristics derived from high resolution satellite image interpretation,were integrated and imported to HEC HMS for the setup of the model. As a result of the delineation, the hydrologic model geometry consisted of 120 sub-basins (or watersheds) draining into the lake. The lake itself was represented as a reservoir in the model. Other elements present in the hydrologic model are 110 reaches, 120 junctions and 1 diversion. Figure 3 shows the interface of the HEC HMS model of Lake Mainit.

Interface of the Mainit-Tubay (incl. Asiga) River Basin

Figure 3. Interface of the Lake Mainit HEC HMS model.

Reservoir Parameterization

lake_mainit_functions

Figure 4. Graphs of Elevation-Discharge Function and Elevation-Area Function of Lake Mainit (see text for references of these graphs).

The reservoir element of the HEC HMS model (Lake Mainit) uses the Outflow Curve Routing method which represents the lake with a user-provided relationship between storage and discharge. The Elevation-Area-Discharge method was implemented which utilized Elevation-Discharge and Elevation-Area functions (Figure 4) as inputs. The elevation and discharge relationship of Lake Mainit was derived using the data from the “Master Plan and Feasibility Study of Flood Control and Drainage Projects of Selected River Basins Nationwide”(DPWH, 2011), while the elevation and area relationshipwas obtained from the research study on the “Limnological and Water Quality Assessment of Lake Mainit”(Tumanda et al., 2003).

Final Model Setup and Simulation

The meteorological model, time-series data of rainfall, and control specification indicating the simulation period were created in HEC HMS.The meteorological model, using the inverse distance method, utilizes the rainfall data recorded by fifteen (15) rainfall stations installed by ASTI DOST. These data were downloaded from the Predict server (http://repo.pscigrid.gov.ph/predict). The selected period for control specification is from January 4-17, 2014 (Typhoon Agaton event) in which notable rainfall values were recorded. During the simulation, HEC HMS utilizes the Elevation-Discharge Function to convert the simulated time series of total discharge flowing into the lake into a time series of water surface elevation or stage.

Results

Shown in Figure 5 is the HEC HMS model simulated lake water levels for the Typhoon Agaton event. It can be observed that the hydrologic model was able to simulate the actual lake water level.

simulated_water_levels

Figure 5. Comparison between the edited stage readings at Kalinawan water level station and the simulated stage readings at the reservoir given the rainfall data from three stations (Kitcharao Municipality, Poblacion and Mainit Municipality).

The computed Nash-Sutcliffe Coefficient of Model Efficiency (E) was computed at 0.97 which indicates acceptable model simulated results. Despite of this good model performance, the calibration and validations of the model still needs to be done so that it can confidently utilized as a water level forecasting model during rainfall events. The forecasts provided by the calibrated and validated model can be useful as basis for early warning of communities around the lake. At present, hydrological data needed for calibration and validation of the model is still being gathered. The automation of the model input, simulation, and output generation is also being done as part of the development of a water level forecasting and flood inundation monitoring system for Lake Mainit called “Flood EViDEns”. This system will not only provide water level forecasts but also flood inundation maps that can be used as basis in the determination adjacent areas to the lake that can be flooded when a certain rainfall event occurs.

Acknowledgements

This study is an initial output of Phi-LIDAR 1.2.14 project of Caraga State University. We acknowledge the financial support provided by DOST PCIEERD, and the UP Diliman DREAM / Phil-LIDAR 1 Team for providing the SAR DEM. The bathymetry of Lake Mainit was obtained from the report of Tumanda et al (2003).

References

Department of Public Works and Highways (2011), Master Plan and Feasibility Study of Flood Control and Drainage Projects of Selected River Basins Nationwide.

Lewis Jr., W. M. (1973). A limnological survey of Lake Mainit, Philippines. Internationale Revue der gesamtenHydrobiologie und Hydrographie, 58(6), 801-818.

Tumanda, M. I., Jr., Roa E. C., Gorospe J. G., Daitia M. T., Dejarme S. M., and Gaid R. D. (2003), Limnological and Water Quality Assessment of Lake Mainit, Mindanao State University, Naawan.

USACE (2000), HEC-HMS Hydrologic Modeling System Technical Reference Manual, Hydrologic Engineering Center, Davis, CA.

Web-based Near-real Time Flood EViDEns for Lake Mainit

flood_evidensThe Phil-LiDAR 1.2.14 Team has developed a preliminary version of an application for flood extent visualization/inundation monitoring for Lake Mainit. Called the Web-based Near-real Time Flood Extent Visualization and Damage Estimations (Flood EViDEns), the app utilizes (at the moment) a 10-meter SAR DEM as source of topographic information. The concept behind the Lake Mainit Web-based Near-real Time Flood EViDEns is that lake water inundation extent can be generated by utilizing water surface elevation (WSE) data recorded by water level monitoring stations in combination with a DTM. Since the lake WSE is known, then we can find those areas within and in the vicinity of the lake whose elevations are equal to the lake WSE. These areas can be considered as inundated. Moreover, as lake WSE is constantly provided by monitoring stations, then it is possible to create and update in near-real time a map of lake water inundated areas.

The Google Map below reflects the initial output of the Lake Mainit Web-based Near-real Time Flood EViDEns. To know the date and time of inundation information, please click on the blue lines.

Click here to learn more about Flood EViDEns and what it can do for you.

[googlemaps https://maps.google.com.ph/maps?f=q&source=s_q&hl=en&geocode=&q=https:%2F%2Fdl.dropboxusercontent.com%2Fu%2F32420108%2Flidar1214%2FLakeMainit.kml&sll=8.889919,125.599136&sspn=0.664146,1.056747&ie=UTF8&t=m&ll=9.433954,125.521566&spn=0.239712,0.106664&output=embed&w=900&h=600]

Long-term Deployment of Sensors in Mainit-Tubay River Basin

The Phil-LiDAR 1.2.14 team deployed datalogging sensors in the Mainit-Tubay River Basin last November 12, 2014. The sensors consisted of a rain gauge, a water level logger, and 2D velocity meter. The deployment has the same purpose to the deployment that have been conducted earlier in Cabadbaran River Basin which is to collect long-term hydrological data (rainfall depth, water level, and water velocity) that will be utilized to calibrate and validate the HEC HMS-based hydrologic models of the river basin. The HEC HMS models consist a major component of the flood models that will be produced by the project.

The rain gauge was deployed on the rooftop of Jabonga Municipal Hall while the water level logger and 2D velocity meter were deployed in Calinawan Bridge, Brgy. Colorado, Agusan del Norte (near the outlet of the Lake Mainit).

The deployment was supervised by Engr. Arthur M. Amora (Senior SRS) together with Engr. Ronald Makinano (Research Associate) and was supported by personnel from the Jabonga Municipal Hall and by the locals.

Long-term Deployment of Sensors in Cabadbaran River Basin

Last November 10, 2014, the Phil-LiDAR 1.2.14 team deployed datalogging sensors in the Cabadbaran River Basin. The sensors consisted of a rain gauge, a water level logger, and 2D velocity meter. The purpose of the deployment is to collect long-term hydrological data (rainfall depth, water level, and water velocity) that will be utilized to calibrate and validate the HEC HMS-based hydrologic models of the river basin. The HEC HMS models consist a major component of the flood models that will be produced by the project.

The rain gauge was deployed on the rooftop of Cabadbaran City Hall while the water level logger and 2D velocity meter were deployed in Cabadbaran Bridge (near the outlet of the Cabadbaran River Basin).

The deployment was supervised by Engr. Meriam M. Makinano (Project Leader) together with Engr. Jojene R. Santillan (Chief SRS), Engr. Arthur M. Amora (Senior SRS), and Engr. Ronald Makinano (Research Associate) and was supported by personnel from the Cabadbaran City Hall and by the locals.