Abstract
Abstract To meet the demand deficit in Kathmandu Valley, the Government of Nepal has planned to supply an additional 510 million liters per day (mld) of water by implementing the Melamchi Water Supply Project (MWSP) in the near future. In this study, we aim to assess the spatial distribution of groundwater availability and pumping under five scenarios for before and after the implementation of the MWSP using a numerical groundwater flow model. The data on water demand, supply infrastructure, changes in hydraulic head, groundwater pumping rates, and aquifer characteristics were analyzed. Results showed that groundwater pumping from individual wells ranges from 0.0018 to 2.8 mld and the average hydraulic head declined from 2.57 m below ground level (bgl) (0.23 m/year) to 21.58 m bgl (1.96 m/year). Model simulations showed that changes in average hydraulic head ranged from +2.83 m to +5.48 m at various stages of the MWSP implementation, and −2.97 m for increased pumping rates with no implementation of the MWSP. Regulation in pumping such as monetary instruments (groundwater pricing) on the use of groundwater along with appropriate metering and monitoring of pumping amounts depending on the availability of new and existing public water supply could be interventions in the near future.
Highlights
Kathmandu Valley’s (KV) water resources management has been dependent on groundwater supply to meet increasing water demands due to the rapid population growth, deterioration of water-related infrastructure, improper land-use planning, and the rapid increase of built-up areas
The majority of the 379 pumping wells are located in the central part of the valley, where the Kathmandu Upatyaka Khanepani Limited (KUKL) is planning to supply water from off-the-valley source via the Melamchi Water Supply Project (MWSP), with 154 wells in the northern groundwater district (NGD), 212 wells in the central groundwater district (CGD), and 13 wells in the southern groundwater district (SGD)
The average change of heads for the valley is 2.83 m. These results indicate that there is a substantial impact on the groundwater system after the completion of the MWSP, especially if proper regulatory mechanisms are able to curb pumping from the deep aquifer by substituting it with the piped water supply to meet any water deficit
Summary
Kathmandu Valley’s (KV) water resources management has been dependent on groundwater supply to meet increasing water demands due to the rapid population growth, deterioration of water-related infrastructure, improper land-use planning, and the rapid increase of built-up areas. Groundwater is considered to be a safe and reliable source of water, resulting in a steady increase in groundwater pumping from the valley’s aquifers (Pandey et al, 2010). The KUKL (previously Nepal Water Supply Corporation) increased groundwater pumping from 2.3 mld in 1979 to 29.2 mld in 1999 (Pandey et al, 2012) and the total estimated pumping including private withdrawals was 59.1 mld in 1998 (Metcalf & Eddy, 2000). In 2009, the estimated groundwater withdrawals reached 70.9 mld (Dhakal, 2010), resulting in a rapid decline of groundwater levels across the valley from 2.57 m to 21.58 m between 2003 and 2014 (KVWSMB, 2012; Shrestha, 2012; Gautam & Prajapati, 2014) below ground surface. Several studies have reported nitrate and Escherichia coli contamination in shallow groundwater as well as a high level of arsenic and iron in deep groundwater, making the valley’s groundwater unsuitable for drinking without pretreatment (Warner et al, 2008; Chapagain et al, 2010; Pathak et al, 2011; Tanaka et al, 2012; Tamrakar & Shakya, 2013; Shrestha et al, 2015)
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