Rainwater Harvesting and Stormwater Management

Urban flooding from even small storms is increasingly becoming a problem worldwide. In addition, this problem contributes to sewage spills, even in developed countries with extensive sewage treatment networks. This is especially a problem in Kathmandu. During a rainstorm, people avoid the Jamal area because it can be flooded with up to half a meter of water, enough to even go into shops along the road. The main road next to Kupondole becomes a river during storms (see photos) as do several other areas.

Why? The goal of current “modern” stormwater systems is to dispose of the rainwater as quickly as possible. This means sending it directly to the sewer. In developed countries, where sewers are maintained, this occasionally results in sewage spills because more water inflows than the sewage treatment can handle. In developing countries, the drains are clogged and it results in localized flooding that many times includes sewage. Both problems exist in Nepal. The only treatment plant that is functioning semi-well in Guheshwori, is non-functional during the monsoon because of heavy rainfall. Flooding is common in every urban area because of poor drainage.

 

 

What is the solution? The point of this post is not to prescribe a solution, but to initiate a discussion and provide information. The irony of Kathmandu’s flooded areas, is that next to them are traditional ponds which are dry in the dry season. Additionally, many of the residents nearby have shallow wells that are dry, sometimes even in the monsoon. Before the paving of roads and the construction of these “sophisticated” sewer systems, these ponds had year round water and the wells provided good water supplies to users. The traditional ponds (pokharis) and stone spouts (dhunge dharas) relied on an interlinked system of groundwater and spring/groundwater-fed canals (rajkulos). Many of these ponds and stone spouts are drying up along with the shallow groundwater depletion.

Currently there are some discussions about improving the drainage in Jamal to send it to the sewer in a better way. This would help the flooding (if it works), but would be extremely expensive. The solution is NOT to send it directly into Rani Pokhari as some suggest, either, untreated and polluted water wouldn’t help the already struggling historical landmark.

Modern cities like New York and Philadelphiaare turning their stormwater into resources, inserting rain gardens, permeable pavement, and other natural technologies to manage and treat stormwater instead of sending it to the sewer. Why are they doing it? Because it is cost-effective. Their current sewage treatment plants can’t handle the rainwater and it is expensive to expand them. The alternative technology works and will save these cities money. They aren’t the only cities following this path.

The current “plan” to improve Jamal’s drainage and send it to the sewer is expensive and will only contribute to the groundwater decline. Instead, perhaps it is worth considering ways to merge modern and traditional technologies and recharge groundwater. If cities such as New York and Philadelphia are finding these to be economical, perhaps they are for Kathmandu as well. The paradigm of stormwater management needs to be re-visited; it’s a resource, not something to dispose of.