Energy Technology Expert

How to help your government and people solve life-threatening and property-damaging events

As a sequel to my earlier blog on “how to predict pre-emptive safe discharge of dam water in anticipation of an incoming storm”, allow me to share my own findings, conclusions and recommendations in order that authorities could formulate a workable and acceptable plan for all the stakeholders in charge of operating and managing dams as well as the affected residents situated at the downstream communities.

This is my own little way of sharing my knowledge, expertise and experience to help my government and country overcome the recurring problem of devastating flooding during the typhoon season.

1) Dams are constructed primarily for flood control with power generation, water supply, water quality control and irrigation during summer as secondary objectives.

2) In a given watershed without the benefit of a dam, flood control will be difficult, if not impossible, since any rainfall that falls on the watershed will immediately inundate the low-lying flood plains of the river system since the volume of water captured in the water basin will surely exceed the maximum safe discharge rate of the river system.

3) Hence, providing ample space for anticipated rainfall in the dam by operating it at a lower level is of most paramount importance than providing storage of water for future power generation, water supply and irrigation.  This main concept has been clearly exemplified by the great damage wrought upon the downstream communities of the Agno River System, Pampanga River System and Angat River System, including that of the Marikina River System.

4) As explained in my blog, it is best to do pre-emptive discharge at a safe rate of around 500-1,000 cubic meters per second (cms) to provide ample space for a significant storm event such as Ondoy or Peping that brought about 120 x 10^6 cubic meters (120 million). A rough calculation showed that around 1 day and 9 hours would be needed to provide this ample storage space when water is spilled from San Roque Dam at 1,000 cms.  Doing a lower discharge of 500 cms will simply double the time of pre-emptive discharge to 2 days and 18 hours or roughly less than three (3) days.

5) In as much as PAGASA is fairly accurate in providing 3-4 day weather forecast from international satellite photographs, even the absence of DOPPLER RADAR at this time should not prevent PAGASA from informing the dam operators to begin a safe discharge and to maximize power generation at the same time.

6) Dam operators should avoid second-guessing the low rainfall from a storm in the event that dam levels have stabilized or in the absence of precise rainfall predictions from PAGASA.  Rather, the use of rain gauges in the watershed plus previous experience should allow dam operators to do simulations to ensure that dam levels are kept at safe levels capable of handling flood waters from an incoming storm.

7) Whenever PAGASA provides rainfall data in millimeters, it also should provide the time frame (i.e. 300 mm/hour or 1,000 mm during a 24 hour period) so that the rate of rainfall and the watershed area will provide the water volume that need to be accommodated by the dam.

8) JICA feasibility study reports normally include a bibliography that provides leads on the source of data, year of measurement and its flood frequency (10, 25, 50, 75 or 100 year flood).

9) There is a need to standardize dam design and downstream dike and flood control systems to withstand a minimum of 25-50 year flood.  With the recent experience of severe damages and loss of lives, surely the benefit to cost analysis by the NEDA should begin to show feasibility of 25 year flood structures and beyond.  NDCC should be able to provide the needed damage reports on a yearly basis.

10) As the river changes in cross section over time, the maintaining of safe velocity should be of primary concern, hence, the need to recalculate the maximum allowable flow of each section of the dike system, and to calculate again the safe discharge of the dam in the event of a spillway discharge.

11) WESM trading rules should be suspended during the adoption of a STORM PROTOCOL so that financial losses of the dam operator will not cloud judgment that will put at risk the safety of the dam and the residents along the floodplain.

12) There are dam management, operation and optimization software in the market for ready use by the dam operators.  There is a need to harmonize data, techniques and identifying downstream discharge constraints so that operating plan and schedules, including discharge rates, duration and time of day, do not coincide with storm events and pre-emptive discharge actions are made part of the operating plan.

I am also attaching my 2008 data on all power plants in the Philippines which needs to be updated with additional information on dam height, area, volume of 1 meter of dam water, design discharge at rated capacity, etc.

Please post your comments and suggestions on how to improve the STORM PROTOCOL to be followed by dam operators before the arrival of a storm event.  The overall objective of the revised PROTOCOL on dam discharge is to allow pre-emptive discharge in anticipation of a storm event in addition to generating power at maximum capacity in order to have adequate flood control capability without resulting in cost penalties to any of the stake holders and dam operators for following the revised PROTOCOL that prioritizes safety over economic issues.

Marcial T. Ocampo

Energy Technology & Pricing

Project Finance & Modeling

Energy & Business Development Consultant