• Bear with floods, PNoy asks public

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    PRESIDENT Benigno Aquino 3rd on Thursday asked for more patience as government agencies attempt to resolve the problem of perennial flooding especially in Metro Manila.

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    He admitted his government’s “limitations” in addressing such serious concern.

    Aquino spoke on two occasions during the day and in both gatherings he talked about what the government is doing to prevent floods based on their supposed master plan.

    “Nagsisikap nga tayong tugunan ang lahat ng kayang tugunan, at ang panawagan ko po: Makiisa at dagdagan ang pang-unawa at pasensiya,” he said in his speech before school officials and students of the Rizal Technological University. Prior to this, Aquino inspected the Manggahan Residences Phase I in Pasig City.

    Aquino explained that there is a “simple” explanation as to why Metro Manila and its environs are prone to flooding. First, he said that water from the Sierra Madre mountain ranges flow down to small rivers and tributaries that are not large enough to contain the volume of rainwater.

    Second, he said catch basins like the Laguna de Bay and even Manila Bay are heavily silted.

    “Aaminin ko po: Lahat ng prob¬lema, gusto nating tugunan—at kung puwede, nagawa na sana natin ito kahapon pa. Pero may mga limitasyon sa kung ano ang maaari nating gawin, at hindi naman puwedeng agad-agad ang pagpapatu¬pad sa isang hakbang,” said Aquino.

    The president bewailed that in Me-t¬ro Manila, only Manila and Ma¬kati City have sewerage and septic systems.

    Besides these structural deficiencies, Aquino noted that the government is facing a number of litigations on the issue of “right of way.”

    Because the National Capital Region has not enough drainage systems and clogged spillways, Metro Manila and surrounding provinces are flooded when there’s a downpour.

    “Ngayon, ang solusyon po natin: Kailangang komprehensibo, buo, at malinaw na Flood Management Master Plan na iprinesenta ni (Public Works) Secretary (Rogelio) Babes Singson kanina. Kasama po dito ang ginagawang Main Drainage Project para sa Mandaluyong,” Aquino further said.

    The Manggahan Spillway housing program is a series of housing projects aimed at relocating residents away from the spillway to prevent clogging and risk to lives and health.

    The project is being implemented by the Department of the Interior and Local Government and National Housing Authority that also aims to keep people away from “danger zones” and for their communities to “build back better” after calamities.

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    1. The solutions to flood problem requires understanding of the hydrologic process and its synergy to the built environment. Mulitiple solutions – because there’s no ‘one-size-fits-all’ solution to the problem. To understand flood phenomenon, you need to understand the impact of the following hydrologic process:

      1.) When precipitation (rainfall intensity) exceeds the rate of absorption of natural ground and the vegetation cover (infriltration) and the environments’ capacity to evaporate (evapo-transpiration) its ambient water/moisture thus producing excess rainwater in the surface (surface run-off)

      2.) Due to natural terrain (topography), surface run-off and infiltrating water (groundwater) will flow to the lowest portion either to the sea/ocean or basins (lakes/ponds/). The transportation mechanism will be the following:
      2a.) For surface run-off, by drainage (gravity flow) through natural conduits and waterways (i.e. rivers and its tributaries)
      2b.) For groundwater, by percolation to the aquifer/aquitard/aquifuge.

      3.) Flood occurs when either or in any combination of the following conditions are satisfied:
      3a.) The intensity of rainfall exceeds the capacity of natural or catchment basins (eg.lakes, flood plain, dams / reservoirs) to contain the volume thus the overflow of surface run-off.
      3b.) The intensity of rainfall exceeds the rate of infiltration/percolation to the ground, and it also exceeds the capacity of the aquifer/aquitard/aquifuge to store water, thus surface run-off.
      3c.) The rate of flow of surface run-off to natural conduits exceeds the capacity of the waterways to discharge/drain to the basins/lakes or open sea/oceans.
      3d.) Extreme change in weather patterns such as strong storm surges, and increasing mean sea level.

      The parameters for flood to occur are:

      A.) Capacity to contain surface run-off
      Factors:
      -Insufficient reservoirs
      -Lack of retention ponds/lakes

      B.) Capacity to store surface run-off
      Factors:
      -Insufficient water sheds and vegetative cover (deforestation, indiscriminate land conversion, etc.)
      -Surface run-off not percolating to the ground aquifer/aquitard/aquifuge
      -Ingress of saline water to the groundwater aquifer/aquitard/aquifuge due to grounwater drawdown or pumping from development areas (eg. residential subdivision using groundwater pumps)

      C.) Capacity to discharge surface run-off
      Factors:
      -Inefficient sewer/stormwater network and system
      -Diminishing natural waterways due to economic development (eg. riverside development, informal settlers)
      -Clogged waterways either by garbage or siltation

      D.) Climate Change
      Factors:
      – Change in weather patterns (extended and/or wetter rainy season,extended and/or drier/hotter summers)
      – Rising sea levels
      – etc.

      Having defined the parameters for flood to occur, the structural solution therefore should address each or in any combination of the following the parameters.

      A.) Capacity to contain Surface Run-off
      – Typical solutions are as follows:
      a.1) Provision for dams and reservoirs
      a.2) Provision for retention ponds & lakes

      B.) Capacity to store
      -Typical solutions are as follows:
      b.1) Watersheds and vegetative cover
      b.2) Artificial Recharging wells
      b.3) Swales

      C.) Capacity to discharge
      -Typical solutions are as follows:
      c.1) separate network for each of the stormwater, residential sewer and industrial sewer lines.
      c.2) increasing waterways capacity either, or in any combination of the following: dredging the river bed, widening the waterways, raising the embankment by providing dikes or levees.
      c.3) reduce the potential of siltation and scouring either or in any combination of the following: bioswales along embankment, baffle chutes to reduce velocity,riprap/gabions/rock armours along embankment,etc.
      c.4) diversion for other purposes such as irrigation, power generation, water supply, transportation, etc.

      D.) Climate Change
      – Typical solutions include:
      d.1) Scenario Planning
      d.2) Improved forecasting techniques
      d.3) Infrastructure adaptation

      As described above, the solutions to flood problem requires a multi-pronged approach and that’s just the infrastructure solutions. The hard solutions should also be complemented by ‘soft’ solutions – i.e. a water policy. This water policy should be a comprehensive water management framework (similar to Water Act in the UK) that addresses water-related issues (such as water supply, flood, drainage, sewerage, wastewater, water shed management, etc.) in a regional or national scale and should be incorporated in the land use zonation planning,natural hazard & disaster risk mitigation plan, infrastructure development plan, and economic development plan of the region concerned.