A retired DPWH design expert who now works as a consultant has proposed a number of innovative projects that would address climate change, promote resiliency and recycle agricultural as well as medical waste.
In his proposal, civil engineer Manuel V. Mapa said rural communities are most exposed to water scarcity as well as flooding, due to erratic weather brought by climate change.
“Innovative designs can abate its disastrous impacts,” he disclosed, “with the inclusion of multiple divergent functions in a single structure.”
For example, he pointed out, an impounding basin that retards flooding can also be transformed into a source of water supply, with the top of the dam structure utilized as spillway road link or bridge to enhance the transport of agricultural products.
This can be an option in the light of the current national policy on El Nino that seeks to mitigate the impending water crisis, Engr. Mapa pointed out.
“This can be done with the use of least-cost soil-cement barrier in impounding flood water in basins and allow the proliferation of fast-growing bamboo and tree species,” he added.
One such innovative flood flow reduction structure would involve a saw-toothed front spillway and concrete baffle barrier on top of the low dams built in series along the river’s path, the former DPWH Bureau of Design chief said.
On the other hand, biochar can be integrated into the innovative designs, as material for concrete, in wastewater treatment and pollution control.
Made by burning organic matter from agricultural waste in a controlled process, biochar is like charcoal but it is lightweight, fine-grained and highly porous.
During pyrolysis, organic materials such as wood chips, leaves or dead plants are burned in a container with very little oxygen and thus release little to no contaminating fumes.
In the process, the organic material is converted into biochar, a stable form or carbon that cannot easily escape into the atmosphere.
Why does this help mitigate climate change?
When materials burn in the presence of an oxygen-rich atmosphere, Green House Gases (GHGs) composed mostly of carbon dioxide are released into the air.
In contrast, pyrolysis traps most of the carbon in the original biomass trapped in solid dorm.
If a fallen tree is chopped up and fed into a kiln, most of the carbon that the tree absorbed from the atmosphere during its life would remain in the resulting biochar.
Research shows that one ton of biochar sequesters or stores carbon that would have otherwise generated 3.6 tons of carbon dioxide if left to degrade by natural processes.
Engr. Mapa said biochar as an innovation catalyst has the value-added capability of imparting more benefits such as: adding compressive strength to concrete structures; providing a plant-based pre-treatment in wastewater treatment using a modified horizontal-flow constructed wetland; promoting sustainable agriculture and food security through increased soil health and water retention; and, reducing pollutants in water that would benefit the fishery sector through better harvests and safe seafood.
In rural areas where the terrain is characterized by mountainous features bounded by narrow and wide coastal plains, at the foothills numerous waterways, either dry or with flowing water exist, he notes.
Small, multiple floodwater weir-type dams constructed in series will be appropriate for such a terrain, Engr. Mapa points out.
The Retarding Weir-Type Rubble Concrete Overflow Gravity Dam
This will have the innovative dual-function of addressing water supply scarcity and floodwater inundation at any given point in time, he stresses.
The gravity overflow dam will be made of concrete with a front side slope of 2:3 ratio. It will have a saw-tooth spillway floor and blocks or baffles on top of the structure to dissipate on-rushing upstream floodwater flow, thus reducing devastating flashfloods downstream.
One or two dams will be best for a flatter riverbed profile while at least two or more will be appropriate fpr a steeper terrain, built in series along the waterway.
The structure has the latent capacity to provide beneficial effects such as impounding floodwater and the river’s natural flow to hasten the recharging of aquifers and groundwater as well as develop forest cover through fast-growing trees and bamboo along the banks of impounded river water.
It will provide additional water source to support permaculture, which is the harmonious integration of landscape and people that will give them food, energy, shelter and other material and non-material needs in a sustainable way.
Permaculture is a practice in land management that adopts compositions discerned in the flourishing natutal ecosystem and is being done in some Asian countries like India and Timor Leste.
Based on the total raw water requirement of 280 liters per hour per person, about 8-10 barangays with a total population of 10,000 need only a discharge flow of approximately 0.50 cubic meters per second form a small river or stream, Engr. Mapa stated.
Supplemented by impounded floodwater, this would be enough to sustain the villages in a “rain or shine” situation.
Adding the innovative decentralized water treatment system for the impounded water as source will be a radical move in any existing water supply treatment system.
In the process, 15 percent of the raw water requirement or 60 liters per day will pass through ultrafiltration water treatment while the rest will be taken up as pretreated floodwater effluent transformed to class C water.
(to be continued)