One question that I encounter a lot is “What will happen to rainwater harvesting after Melamchi comes?” Until recently, it was a question fairly easily ignored since Melamchi seemed like a literal pipe dream. Then as the years went on, Melamchi progressed very quickly including the equally necessary distribution pipe improvements.This means that the targeted 2018 completion date and delivery of water is likely.
Melamchi is a much-needed project for Kathmandu. Better municipal water means a healthier population and less groundwater extraction. One must applaud the progress of the project, although we would have wished for a little less dust.
But once snow melt from Melamchi starts flowing into our taps, does it mean rainwater harvesting is no longer necessary? No.
Melamchi is years late, it was originally forecast to meet the demand at the beginning of the new millennium. Now the demand is approaching 400 million liters per day, with a current wet season supply of 150MLD before leakage. That is a shortage of 250MLD, excluding leakages, which is more than Melamchi Phase 1 will bring. Rainwater harvesting for direct use is still needed to reduce continued groundwater extraction.
Even before 2000, groundwater over-extraction from deep wells in Kathmandu was already a problem. Additionally, shallow groundwater depletion is obvious with household and community wells, dhunge dharas, and local pokharis going dry.
Before cities were made, stormwater infiltrated into the ground through farms, forests and grassland. Now stormwater washes pollutants off the roads and (sometimes) flows into wastewater treatment systems. In a monsoon climate, like Nepal where nearly 1.5 meters of rainfall is packed into six months, this creates an undue burden on wastewater treatment systems. It also makes a high risk for combined sewer overflows, where heavy rainfall causes untreated wastewater from working wastewater treatment systems to overflow into the river. Already, there are problems with the few existing, partially functional, systems in Kathmandu stormwater flows make them worse.
Combined sewer overflows are a problem even in cities like New York and Philadelphia which are investing billions into natural retention and recharge systems (Green Infrastructure) to minimise wastewater costs and sewage spills. These interventions were chosen because of their cost-effectiveness, both in up front capital and operation costs, and the many secondary benefits.
Green Infrastructure includes various technologies to trap and replenish rainwater, including green roofs, rainwater collection and recharge, bioswales, permeable pavement, rain gardens and more. Many of these technologies are attractive and cost-effective, and rainwater harvesting is already well-recognised and practiced in Kathmandu.
Kathmandu is blessed with an amazing network of historical water infrastructure, from stone spouts to pokharis to community wells. This infrastructure should be restored as well. One way to help do this, especially for many of the historical ponds and some stone spouts, is increasing recharge again. This can be done in a combined way through modern green infrastructure like other cities are investing in, and restoring old, historical sites with a bit of creativity.
In addition, Green Infrastructure have many secondary benefits including carbon sequestration, urban heat island mitigation and green spaces, reduced energy demand through shading from vegetation, improved air quality and quality of life. There are other good examples of rain gardens being used to offset areas for pedestrians and cyclists from the roads.
Kathmandu Valley has a good opportunity to do this right now, especially with newly elected Mayors and Ward Committees. All of them are talking about water, energy and sustainable transport and this can be one way to help clean up Kathmandu. Since everything is being dug up, the right time to invest in this infrastructure, instead of the large sewers which are coming later, is now.
Kathmandu has an advantage because rainwater harvesting (left) has gained momentum over the past decade and a growing body of data on groundwater and recharge potential is also becoming available. The only thing remaining is continued coordination between government agencies including the road, electricity and wastewater treatment works.
Five wastewater treatment plants are being built, so integrating stormwater planning, rainwater harvesting and other green infrastructure (including household incentives for their own systems, including already built ones), and historical water infrastructure planning with the future plans for wastewater treatment will be the next step.
Tyler McMahon is an adviser at One Planet Solution and SmartPaani
Melamchi not a mirage anymore, Sonia Awale
Pipe water still a pipe dream, Kenji Kwok
What to do while waiting for the Melamchi mirage, Bhrikuti Rai
Going with the flow, Liew Yu Wei
No water? No power? No problem, Bhrikuti Rai
Investing in rain, Bhrikuti Rai