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Chapter IV A. Groundwater Use inKathmandu Valley

Abstract:

The Kathmandu Valley, bowl shaped of 651 Km2 basin areas, has gently sloping valley floor, valley plain terraces with scrap faces together with the flood plains. The valley has warm temperate-semitropical climate and intended circular shaped drainage basin with only one outlet. The valley is filled with the fluvio-lacustrine sediments of quaternary age, making three groundwater zones. Only one water supply operator, Kathmandu Upatyaka Khanepani Limited (KUKL), is serving water supply in 5 Municipalities and 48 VDCs out of 99 VDCs using 35 surface sources, 57 deep tube wells, 20 WTPs, 43 service reservoirs and operating about 1300 major valves. The portion of groundwater contribution in total production is an average of 35% in dry season and 11% in wet season with yearly average of 19% in 2011, and found decreasing to 7%, 4%, and 3% in 2016, 2019 and 2025 respectively. Water supply is found to be improved with increasing consumption rate from 41 lpcd in 2011 to 126 lpcd in 2025.If supply system is managed with project demand of 135 lpcd, the average supply duration will increase from 7 hr a day in 2011 to 23 hour a day in 2025. Foremost reasons of supplying much less compare to calculated are possibly due to inaccurate forecasting of served populations, absence of effective MIS on water infrastructure systems, and inaccurate estimation of unaccounted for water from system. Outside valley urban centers development, optimum land use planning for potential recharge, introducing micro to macro level rainwater harvesting programs and riverhead forest protection are important alternative options to minimize the gap between demand and supply of the valley.

1. BACKGROUND

The Kathmandu Valley is consisting of Kathmandu metropolitan city, capital of Nepal. Kathmandu, an ancient city with a varied history, consists of Kathmandu, Bhaktapur and Lalitpur districts with five municipalities and 99 Village Development Committees. The significance of its historical development is the rise of conurbation in the valley, the design of Pagoda style architecture and high rising temples with stepped plinth basement. After liberation in 1952, the new phase of development began with remarkable change in social status, migration of people to the valley. The general trends of the urbanization remained slow till the mid sixties. Only in seventies, infrastructures like road networks, water supply systems started to develop rapidly in the city. As a result, the valley is growing rapidly and haphazardly. This is the right time to look seriously at the growing urban problems and available water resource in the valley. It is necessary to systematize the settlement, implement the town planning more scientifically and carry out the land use in proper manner so that available water resource potential could be maintained sustainably. There are various development plans for the valley, namely construction of outer ring road, fast track road, railways, urban settlement development and construction of link roads on the bank of the rivers. The shortages of surface and groundwater availability and flood damage are identified problems in the valley. The valley basin is an ecologically important basin.

2. INTRODUCTION:KATHMANDUVALLEY

2.1 Topography

The Kathmandu Valley is an intramontane basin, situated in the Lesser Himalayan zone. The lofty Higher Himalayan Range is just about 65 km aerial distance north of the Kathmandu. The valley is unique in its shape and is surrounded by the spurs of Lesser Himalayas. The valley basin is 30 km long in the east-west and about 25 km long in north-south direction. Phulchoki Hill which is 2762m above the mean sea level (msl) in the southeast is the highest elevation point in the area. Shivpuri Hill is about 2700m above msl in the north, Nagarkot is 2166m above msl in the east and Chandragiri is about 2561m above the msl in the west. The lowest elevation point located by the side of Bagmati River is 1214 m above msl. About 55 % of the area is occupied by the valley floor, 35% of foothill and the remaining 10% are mountainous areas. In the valley, the forest (mountainous) area is about 30% of the total area having slope range from 20 to 30%, and remaining area (70%) is having average slope of 0 to 4% as shown in Fig.1.

Kathmandu Valley is believed to be a Paleolake. At places outcrops of Tistung Formation are exposed in the valley. There are few other buried hills and river channel in the valley underlying the thick cover of the valley fill sediments. Kathmandu Valley is situated between latitudes 27°32' N and 27°49'N and between longitudes 85° 11' E and 85° 32' E. The configuration of the valley is more or less circular with watershed area of 651 km2.  The topographic features of the study area are gently sloping valley floor, valley plain terraces with scrap faces, and talus cone deposition, together with the flood plains.

2.2 Meteorology

The climate of the area is warming temperate-semitropical, largely affected by monsoon behavior. The maximum temperature is observed about 36° C in summer (May) and the minimum temperature is about -3°C in winter (January). The major forms of precipitation are rain, occasional hail and fog.  Considering the precipitation received record the maximum annual precipitation within the valley was recorded as 3293 mm in 1975 and minimum was 917 mm in 1982. The summer rainfall occurs mainly in the months of June to September and winter rainfall is also common but not heavy. Kathmandu Valley receives an annual average rainfall of about 1600 mm, which is also the average annual rainfall for the whole Nepal.

The mean relative humidity is 75% and the mean wind velocity rises till the month of May up to average of 0.55 m/s and decreases after monsoon until December. The predominant wind directions are west and northwest. Generally the days are rather calm before noon and the wind rises afternoon. The monthly air pressure is almost constant throughout the year, which is about 860 mb. The sunshine duration is in the range between 7 hours and 9.5 hours per day except during the months of monsoon.  The average annual evapotranspiration is 829 mm over the basin.

2.3 Drainage

The valley is situated at the upstream reach of the Bagmati River. The Bagmati River is the main drainage, which drains all the water collected in the valley basin to the south and dissects the mountains of Mahabharat range at the southwest of the valley. It originates from Bagdwar in the Shivpuri Hill in the north and flows from northeast to southwest direction in the northern half part of the valley. The watershed area has an intend shape of circular with the outlet of the basin at Chovar gorge, which is the only outlet of the basin. The fluvio-lacustrine deposit filled in the valley bottom controls the drainage system. The major tributaries for Bagmati river are nine in total namely Mai khola, Nakhu khola, Balkhu khola, Vishnumati khola, Dhobi khola, Manohara khola, Kodku khola, Godavari khola and Hanumante khola. Hanumante khola flows towards the west and Balkhu khola towards the east. Mai khola and Dhobi khola flow towards the south. They meet Bagmati River in the central part of the valley. The Vishnumati, the Bagmati and the Manohara khola, which rise from northern and northeastern of the watershed, join in a place called Teku Dovan in Kathmandu City. Godavari khola, the Kodku khola and the Nakhu khola rise in the southern part of watershed and flow from the south to north to join with the Bagmati River.

2.4 Hydrogeology

Hydrogeological condition of the valley is important things to know the groundwater potential and its yield estimation. The valley is located in the Lesser Himalayan region in central Nepal. Bedrocks are exposed mainly in the hill slopes around and only at few places in the valley.  The valley is filled with the fluvio-lacustrine sediments of quaternary age. These sediments were derived from the surrounding hills. The thickness of the valley fill sediments varies according to the undulated pattern of the basement from 78 m in Bansbari upto 549 m in Bhrikuti Mandap as confirmed by deep bore holes (Kaphle and Joshi, 1998). Metasedimentary as well as metamorphic rocks represent the basement/bedrock of the valley. Shrestha(2001) assigned The Hydrological Soil Group (HSG) for each type of geological formation according to its infiltration potential as per SCS (1975). HSG A was assigned for the soil of high infiltration rate, B for medium, C for slow and D for very slow rate. The HSG of the valley is shown in Fig.2.

There are two types of sediment material namely unconsolidated and slightly consolidated sediment materials. The unconsolidated materials are found mostly in the northern part of the valley and bank of major rivers whereas slightly consolidated materials are found in other portions. In the valley, silty clay lake deposit ranges in thickness from 180 to 220 meters or more from surface and are predominate in the center and south of the valley. On the other hand no thick silty clay lake deposit exists in the northern valley except deep portion of Dhobi khola well field. Un-confined to semi-confined sand and gravel formation predominate in the north and northeast of valley. These formation ranges in thickness from 30 to 80 m with high permeability. On the other hand, the confined water bearing formation is underlined the above mentioned very thick silty clay in the center and south valley. However this deep aquifer has low permeability and high electrical conductance. The ground water wells in the north side have penetrated high permeable water bearing formation.  However, the static water level in well field as observed by Nepal Water Supply Corporation (NWSC) has been showing a decline trend since the groundwater development has started. Almost all the private wells are located in the center and south of the valley, drilled into the confined low permeable aquifer underlined the very thick silty clay formation. In the center of the valley, below Quaternary sedimentary formation, pre-Palaeozoic hard fresh rocks are confirmed by gas wells at 450 m below ground surface.

3. GROUNDWATER ZONE AND RECHARGE

Recharge into groundwater is a complicated phenomenon especially when considering recharge in a deep aquifer. It depends on many factors such as soil, vegetation, geography, and the hydrological conditions. In general, most of rechargeable areas are confined in high flat plains and alluvial low plains in the valley, because the exploitation of groundwater seems to be difficult in the surrounding high mountains. The mountain ranges surrounding the valley have no possibility for groundwater recharge because of the high relief topographical conditions. Due to steep slope, the rainfall will convert quickly to runoff than infiltrate through the ground and joins the nearest tributaries. Most of the permeated rainfall moves laterally and reappears in to the river channel as base flow or lost as evapotranspiration. The remaining part moves vertically and recharges the groundwater basin. So the rechargeable areas are found on the margins of northern and southern part of the groundwater basin boundary. Groundwater basin boundary has area of 327 km2 (Shrestha, 1990). The total rechargeable area in the valley was found 86 km2 which is 26% of the groundwater basin area. The amount of long term average annual groundwater recharge to the Kathmandu Valley basin was estimated as presented in Table 1.

Table 1. Recharge Amount in equivalent depth over the Kathmandu Groundwater Basin

(Shrestha, 1990)

Recharge amount in equivalent depth  over the basin per year

Recharge  Calculation Methods

51 mm

Water Balance Method

55 mm

Base flow separation Method

37.5 mm

Specific Yield Method

59 mm

Chloride Balance Method

41 mm

Groundwater Flow Method

In 1972, the incoming tritium content at Kathmandu valley was estimated by the Atomic Energy Research Establishment (AERE), Harwell, 60 TU (Tritium unit) during summer and 30 TU in winter. The Tritium dating result for the groundwater indicated the recharge water was of pre-1954 (Binnie & Partners and Associates, 1973).

Based on hydrogeological structure the valley can be divided into three groundwater zone, namely Northern, central and southern zone.

  • The northern zone includes 5 well fields ( Bansbari, Dhobikhola, Manohara, Bhaktapur and Gokarna well field)  as principal water sources and of 157 km2 area with estimated recharge area of 59 km2 ( Shrestha, 1990). The northern zone is largest recharge area of the valley. There are unconsolidated high permeable materials deposits in upper part consisting of micaceous quartz, sand and gravel. It can yield large quantity of water. Isotope analysis study made by Jenkins et al, 1987, confirmed that there is more rapid and vigorous recharge in Sundarijal area (Gokarna well field) than elsewhere. This zone is an interbedded aquifer or a series of sub aquifers and the complexity of its structure. It has average transmissivity in range of 83 to 1963 m3/d/m and low electrical conductivity in the range of 100 to 200 ms/cm.
  • The central zone includes most of core urban area with almost all private wells. This zone includes Mhadevkhola well field. The upper part of deposit is composed of impermeable very thick stiff black clay with lignite. Total groundwater basin under central zone is 114.5 km2 and the rechargeable area under this zone is 6 km2. It has average transmissivity in the range of 32-960 m3/d/m and very electrical conductivity of an average of 1000 ms/cm. The existence of soluble methane gas gives an indication of sustended aquifer conditions.
  • The southern zone is characterized by about 200m thick clay formation and low permeable basal gravel. This zone is not well developed and only recognized along the Bagmati River between Chovar and Pharping. Total groundwater basin under this zone is 55.5 km2 and the rechargeable area is 21 km2. This zone includes Pharping Well field.

4. WATER SUPPLY MANAGEMENT STATUS IN KATHMANDU VALLEY

4.1 Institutional Set up and Service Area

The water supply services of Kathmandu Valley have remained poor despite various attempts through many projects during last three decades. It was realized that the poor state of water services in Kathmandu valley was a compounded result of deficiencies in water resources, weaknesses in system capacity, inadequacies in management efficiency and increasing political interferences after 1990 political change. As per agreement made with ADB for Melamchi Water Supply Project (MWSP), the Government of Nepal restructured the existing only one State owned regulator  and operator , Nepal Water Supply Corporation (NWSC) and establishing three separate entities, each for the role of asset ownership and policy setting (Kathmandu Valley Water Supply Management Board (KVWSMB), operation and management of services (Kathmandu Upatyaka Khanepani Limited (KUKL) and economic regulation of the services (Water Supply Tariff Fixation Commission (WSTFC).   KVWSMB issued an operating license to KUKL for 30 years on 12 February 2008 and also signed asset lease agreement for 30 years. Under the Asset Lease Agreement, KUKL has exclusive use of leased assets for the purpose of providing water services over 30 years and is responsible for maintaining the leased assets in good working condition, preparing capital investment and asset management programs to meet the service standards specified in the license and implementing such investment plan as approved by KVWSMB. As provider of the license, KVWSMB is also responsible for monitoring whether KUKL complies with the provisions of the operating license and asset lease agreement. The service area of KUKL includes 5 Municipalities and 48 VDCs as shown in Fig. 3.  Water supply management for remaining 51 VDCs are under Department of Water Supply and Sewerage, Government of Nepal.

4.2 Population Projections

The Kathmandu Valley is the most densely populated region in Nepal. Its population has also been increasing rapidly. This population is largely in Kathmandu, which is the centre of administration, industrial, commercial, social and economic activities. During the last three decades, the growth in population has been significantly driven by in-migration. The in-migration is largely due to better employment and business opportunities, better educational and medical facilities, but also insurgency and security concerns of recent years.

(Source: KUKL 2011 Third Anniversary Report, 2066/67)

The rapid unplanned urbanization of the Kathmandu Valley has brought negative impact to its overall development. Water became scarce as demand exceeded supply. Lack of operational wastewater system facilities converted the holy Bagmati River into a highly polluted river. Congested and crowded roads brought hardship to travelers and road junctions became garbage dumping sites. Despite these negative impacts, the urbanization of the valley has still continued at a similar rate to the past 10 years. According to urban planners, from urban basic service management and disaster relief management aspects, the Kathmandu Valley only has a carrying capacity of 5 million populations.

In 1999, the Ministry of Population and Environment (MOPE) estimated that the population in 1998 was 1.5 million, assuming an urban growth rate of 6.3% and 2.32% for the rural sector. This is consistent with the 2001 Census of 1.67 million. Using separate growth rates for the urban and rural population, the population of the valley was estimated to reach 3.5 million by 2016 under a "do-nothing scenario" according to MOPE (1999), as shown in Table 2.

Table 3 shows the projected population in the Kathmandu Valley and KUKL service area upto 2025. Population in Kathmandu Valley will be saturated with maximum capacity of 5 millions in 2025. Thus alternate planning and development of urban settlements are needed after 2025.

Figure 4 shows comparison of the KUKL service area permanent population projections adopted with those provided by SAPI (2004) and the Bagmati Action Plan (BAP) (2009). The BAP projection is higher because the area taken is for the whole of the Kathmandu Valley and includes areas outside the KUKL service area.

Table 2. Population Projection for Kathmandu Valley under "Do-nothing Scenario"

Year

Total

Urban1

Rural2

1991

1,105,379

598,528

506,851

1996

1,369,403

800,965

568,438

2001

1,709,380

1,071,872

637,508

2006

2,149,378

1,434,407

714,971

2011

2,721,406

1,919,560

801,846

2016

3,468,082

2,568,805

899,277

Note: 1 Growth rate at 6% per annum, 2, Growth rate at 2.32% per annum.

Urban population includes municipal population and population of 34 rapidly urbanizing VDCs, Source: MOPE, 1999

Table 3: Projected Population for Kathmandu Valley and KUKL Service Area Year

Year

2001 (census)

2010

2015

2020

2025

Kathmandu Valley

1,579,737

2,712,000

3,486,000

4,481,000

5,761,000

KUKL Service Area

1,285,737

2,135,000

2,713,000

3,242,000

3,963,000

Source: Kathmandu Valley Water Supply & Wastewater System Improvement ( PPTA 4893- NEP)  May 2010)

5. WATER INFRASTRUCTURES (KUKL)

Figure 5 shows 6 major water supply schemes, namely, Tri Bhim Dhara, Bir Dhara, Sundarijal, Bhaktapur, Chapagaun, and Pharping schemes, which include surface and groundwater sources, WTPs, and major transmission lines.

Surface Water Sources: At present, there are 35 surface sources being tapped for water supply mostly situated at hills surrounding the valley as spring in the valley. There is considerable seasonal fluctuation in water discharge. Most water sources have a reduced flow in the dry season by 30 to 40% with some by as much as 70%. Almost all the sources have some potential additional yield in the wet season. The total wet season supply of 106 MLD reduces in the dry season to 75 MLD.

Groundwater Sources: Deep tube wells are the main means of extracting groundwater for use in the water supply system. Out of 78 existing deep tube-wells only 57 are currently in operation mainly from 7 well fields, namely, Manohara, Gokarna, Dhobikhola, Bansbari, Mahadevkhola, Bhaktapur, and Pharping well fields. Most of the tube wells electro-mechanical parts are in a poor condition with most flow meters missing or broken. Tube wells used to be operated only in the dry season in order to supplement reducing surface water sources, but, due to demand exceeding supply, they are now also used in the wet season. Total dry season (4 months: February to May) rated production 33 MLD with a reduced wet season (remaining 8 months) production of 13.7 MLD. Additional subsurface flow has been extracting through 15 dug wells. Table A1 (in Appendix) presents inventory of deep tubewells currently in operating condition in KUKL.

Water Treatment Plants: At present, there are 20 water treatment plants (WTPs) in the system with a total treatment capacity of about 117 MLD treating surface water and groundwater due to high iron content. Six WTPs are of capacity between 3 to 26.5 MLD. The largest is at Mahankal Chaur with a treatment capacity of 26.5 MLD and the smallest is at Kuleswor with a treatment capacity of 0.11 MLD. Most of the WTPs are in poor condition and none has operational flow meters or properly operating chlorination equipment.

Service Reservoirs:  There are a total of 43 service reservoirs in the system with capacities ranging from 4,500m3 down to 50m3. Most of the reservoirs are in reasonable condition but two are leaking. The total storage capacity is 41500 m3.

Pumping Stations:There are 31 water supply pumping stations in the system that are used to draw water from sump wells to treatment plants or service reservoirs, and to fill up reservoirs located on higher ground or overhead tanks. Of these only 11 are in satisfactory condition. Few have operational flow meters or pressure gauges. Major operation and maintenance problem in the pumping stations are lack of skilled technician and absence of proper monitoring mechanisms.

Transmission Mains and Distribution Lines: At present, the total length of transmission mains is about 301kms,aging between 20 to 115 years, and distribution mains of about 1115 kms of aging between 2 to 115 years, with pipe diameter varying from 50mm to 800mm. The pipe materials used include Galvanized Iron (GI), Cast Iron (CI), Steel (SI), Ductile Iron (DI), High Density Polythene Pipe (HDPE) and Polyvinyl Chloride (PVC). The majority type of pipe used is 50mm diameter GI.

Operating Mechanism:  The system has about 1300 major valves of different sizes. Most of the large sizes valves are situated inside WTPs and operating daily. All valves are being operated manually. Water leakage from the valve chamber or valves contributes major portion in the total counted leakage percentage. Other than piped water supplied through the valves, water tankers are also serving water especially in water scared area by injecting into the distribution line usually smaller size (50 mm) and filling in publicly established polytanks. Water tankers are also being used for emergency condition such as pipeline breakage, fire fighting and sudden malfunctioned systems. Water tankers are also used as private trip charging approved rate. There are many problems in the distribution system. These problems include: ad hoc laying of pipes and valves, involvement of users' group and their intervention in the operation of valves, multiple service pipeline connections, direct pumping from distribution lines, illegal connections, high percentage of leakage and wastage, and direct distribution from transmission mains. The majority of consumer lines are leaking at the connection to the distribution mains and few customers have properly operating consumer meters.

6. WATER DEMAND AND GROUNDWATER USE FORSUPPLY

6.1Current Water Demand and Supply

Water demand is usually derived from the population within service area, population growth, domestic water consumption level assumptions, and a provision for non-domestic water consumption. The permanent population is forecast to rise from present population of 2.1 million in 2010, 2.7 million in 2015 and 3.2 million in 2020 and 3.9 million in 2025. Out of the total population forecast 77%, 87% and 96% of the population will be served, as a result of the MWSP and future investments, in 2015, 2020 and 2025 respectively. Predicting the exact number of temporary population in the valley is a challenging task, as there is no reliable data. Kathmandu Valley Water Supply & Wastewater System Improvement-PPTA 2010, undertook a sample survey to count temporary population. The sample surveys were focused on three categories of the temporary population viz street vendors; students, service holders and labours seeking job in the valley; and house servants/keepers. The survey indicated that temporary population amounted to approximately 30% of the permanent population. The proportion of temporary population varies between municipal and VDC wards. It has to be taken into account in population projections and service demands.

However, demand is also a function of price, household income availability and accessibility of water supply, but accurate estimates of the impact of these factors require extensive analysis of historical data. The present permanent population of the valley water supply service area is estimated at over 2.1 million. Adding 30% the total population to be considered for gross demand forecasting will be 2.73 million. It is reasonable to assume 40 % of total water consumption rate for temporary or floating population. Considering household sanitation system in the service area, it is reasonable to take per capita demand in the range of 85 to 95 lpcd. Kathmandu Valley Water Supply & Wastewater System Improvement-PPTA, 2010, has considered 93 lpcd. For the demand taking 135 lpcd which is consumption rate considered in MWSP for total population including temporary population, the total water demand at service level or point of use is found to be 315 MLD, which is similar to KUKL estimated demand of 320 MLD (KUKL, 2011). Estimated unaccounted for water (UfW) considered for the system is 35-40% (KUKL 2011). Considering UfW as 40 %, net water supply would be decreased by 40%.

Figure 6 shows maximum production of 149 MLD on the month of September and minimum of 89 MLD on March. It gives yearly average production of 119 MLD and dry season average production of 94 MLD whereas wet season average is 131 MLD.

Considering 20 % real losses as process loss on water flow incorporating transmission loss, treatment plant operation loss, quantity of water supplied and deficiencies is estimated as shown in Fig.7 and Table 4. 20 % loss is assumed to be occurred in distribution system, i.e. from service reservoir to a tap or point of use.

Table 4. Current Average Monthly Demand, Supply and Deficiencies

Month

Demand, MLD

Production, MLD

Supply, MLD

Deficiencies , MLD

Jan

315

114 (13.5)

91

224

Feb

315

99(33)

79

236

Mar

315

89(33)

71

244

Apl

315

95(33)

76

239

May

315

96(33)

77

238

Jun

315

114(13.5)

91

224

Jul

315

141(13.5)

113

202

Aug

315

145(13.5)

116

199

Sep

315

149(13.5)

119

196

Oct

315

142(13.5)

114

201

Nov

315

132(13.5)

106

209

Dec

315

116(13.5)

93

222

( ...) Groundwater contribution in MLD

Figure 7 shows dry season average supply as 76 MLD and 105 MLD for wet season. Yearly average supply is 96 MLD. Thus the water supply in the Kathmandu Valley via KUKL piped network at present is an average 35 litres per capita per day, whereas supply in KUKL service area is average of 46 lpcd.

6.2Groundwater Depleting Trends

The portion of groundwater contribution in total production is an average of 35% during dry season (4 months from Feb to May) and 11% during wet season (remaining 8 months). The pumping rate of the private wells in the valley is smaller compared to KUKL's  tubewell abstraction. The trend of groundwater extraction volume from private wells and gas wells remains almost constant during the last several years. But the production from KUKL wells is increasing greatly. Deeper groundwater is being over-extracted and extraction is unsustainable. It is estimated that there are over 10,000 hand dug well which are used to supplement the KUKL water supply. More reliable water supplies will reduce the need for groundwater pumping, thus allowing more sustainable use of this valuable water resource.

JICA (1990) had used historical well hydrographs to assess the seasonal fluctuation of groundwater level and recharge into main aquifer in the study of groundwater management of Kathmandu Valley. Tank Model (Sugawara et al.1974) was used for simulation to develop the relationship between rainfall and groundwater level. The annual fluctuations (maximum groundwater level- minimum groundwater level) of long-term average at two sites were estimated. In the study, they estimated mean annual fluctuation on well WHO 7A (Sundarijal) by taking average over the period 1940-1986 as 1500mm and on well B12 (Maharajgunj) over 1947-1975 as 457 mm. Both wells are located in the northern part of the basin. The groundwater level has an annual cycle.

The Kathmandu Valley groundwater basin can be isolated from other groundwater bodies outsides the valley. The recharge through outside the valley is assumed to be negligible. The groundwater levels have been in nearly steady condition in the early stages of the 1980's, because no large well was operated at that time in the basin. JICA (1990) has developed relationship by trial-and-error method in order to make the calculated groundwater level of the main aquifer to coincide with the observed one. Extraction of groundwater by pumping has found to be increased since 1984 so it is worth to assume that groundwater level was in a steady state condition on and before 1983.

Groundwater assessment model developed by Shrestha (2001), has found groundwater level  decreasing sharply from 1985 onwards and balanced water available was abruptly changed from 1986 onwards. The model had assumed initial groundwater storage as 1000mm to calculate relative drawdown of the groundwater. The model predicted the maximum soil moisture content as 225 mm which had been found in the range of 200 mm to 250mm estimated by Binnie & Partners and Associates (1973) for the Kathmandu Valley. He used mean annual actual evapotranspiration calculated by Shrestha (1990), as 829 mm while the mean annual potential evapotranspiration was 1074 mm. An annual actual evapotranspiration was found almost constant for the valley. Some recharge areas, which are on the northern part of the valley, is converting to urbanization rapidly. On the other hand, extraction of groundwater is also increasing to fulfill the demand of water. These are the main reasons for rapid reduction of groundwater storage.

The drawdown was calculated with reference to the year 1975. The initial condition of groundwater level is taken as of the year 1972. The drawdown depth observed in the valley basin was much closed with observed drawdown for all observed years. The model has found three distinct trends of drawdown such as decreasing trend from 1977 to 1981, increasing trend from 1981 to 1985 and sharp increasing trend after 1986. Main reasons behind sharp increasing trend of drawdown were listed as three to four fold increasing in new house constructions and over extraction of groundwater to cope shooting water demand due to rapid and unplanned urban growth. The total basin equivalent drawdown was found to be increased by 2.75 m in year 1984 and 7.5 m in year 1989 when compared to that in the year 1978. The model predicted drawdown only due to groundwater extraction was found to be increased by 2 m in the year 1984 and 6m in the year 1989  compared with the drawdown during 1978. Shrestha (2001) concluded that drawdown of 0.75m in the year 1984 and 1.5 m in the year 1989 could be attributed to the hydrological change due to land-use modifications.

7. POST MELAMCHI SCENARIO AND EXPECTED STRESS IN FUTURE

It will be reasonable to assume that The Melamchi water will be served its first phase to the alley by 2016. According to the prediction (Referring Figure 4), the permanent population of the service area will be 2.8 millions in 20016. According to urban planners, from urban basic service management and disaster relief management aspects, the Kathmandu Valley only has a carrying capacity of 5 million populations and it would cross the capacity by 2025.

MWSP is a comprehensive multi donor water supply mega project that aims to improve the health and well-being of the people in Kathmandu Valley. It will achieve this impact by diverting water from the Melamchi River to the Kathmandu Valley and thus deliver its overall outcome of alleviating the chronic shortage of potable water. MWSP is implemented under two subprojects. Subproject-1 delivers bulk potable water to the head of the Kathmandu Valley (Melamchi Diversion Scheme). Its major civil components are the 26 km tunnel and the new water treatment plant at Sundarijal. MWSP subproject-2 has major civil components of water distribution system and wastewater system improvements in the valley. MWSP has aimed for 24 hours water supply of 135 lpcd and structured water infrastructure rehabilitation and development programs under subproject-2 as listed below, to reduced UfW to 20% from 40%. It can be divided into two portions. 10% loss is assumed to be occurred in transmission and treatment process and another 10 % in distribution system.

  • Rehabilitation and Development of Surface Water and Groundwater Sources
  • Rehabilitation and Development of WTPs
  • Bulk Distribution System
  • Water Supply Service reservoirs repair and New construction
  • Distribution Network Improvement (DNI)
  • Land Acquisition for the programs

MWSP has been conceived to divert 510 MLD of water to the Valley in three phases. In the first phase a total of 170 MLD of water would be diverted and followed by subsequent development of Yangri and Larke river system to the tune of 170 MLD each in next two phases. It is expected that first phase Melamchi Water will be added in 2016 and other additions of 170 MLD in 2019 and in 2025.

Table.5.Pre and Post Melamchi Scenario on Demand, Production, Supply, Groundwater Contribution and Supply Hour per day for 2011 and 2016

Table 5 presents calculated water demand after first phase of MWSP completion  i.e. on 2016, as 423 MLD serving permanent population of 2.8 million and temporary population of 0.84 million (30% of permanent population ) with 135 lpcd 24 hour supply. Average Water Production including additional 170 MLD with average groundwater contribution of 7% is 288.96 MLD. Supply is calculated considering 10% transmission and treatment process loss and average supply as 260.06 MLD. Liter per capita per day (lpcd) is evaluated considering supply quantity for total effective population (2.8 +0.3 x 2.8 = 3.64 millions), but only 40% of consumption rate is considered for temporary population. It shows an average lpcd of 82.9 lpcd serving the total population with 24 hour supply. If supply is managed with project demand of 135 lpcd, the average supply duration per day will be of 14.74 hours.

Table.6.Pre and Post Melamchi Scenario on Demand, Production, Supply, Groundwater Contribution and Supply Hour per day for 2019 and 2025

Figure 8 shows the MWSP will increase average lpcd from 40 lpcd in 2011 to 126 lpcd in 2025.  If supply system is managed with project demand of 135 lpcd, the average supply duration per day is also increased from 7 hr a day in 2011 to 23 hour a day in 2025. Table 6 Figure 9 show decreased average groundwater contribution from 19 percent in 2011 to 3 percent in 2025.

8. CONCLUSIONS

Considering water supply scenario of 2011, average water supplied at the point of use will be 57 MLD taking 40% UfW (KUKL, 2011) and consumption rate of the supply is 24.27 lpcd. Supply duration per day is calculated as 4 hour if considered 135 lpcd. But the supply hour is much less than calculated as present condition of KUKL water supply. Major possible reasons which make difference with actual conditions might be listed as:

  • Inaccurate forecasting of served population
  • Absence of effective MIS of Water Supply System
  • Inaccurate estimating UfWs ( transmission, treatment and distribution)

It is found that MWSP alone is not sufficient providing water supply to cover forecasted served populations. Alternative sources should be planned and added. Another option will be, if outside the valley urban settlement development planning is formulated and implemented, the population growth rate will be controlled or it may be decreased mainly due to migration of new population to outside the valley.

Effect of land-use modification is more predominant in groundwater than on the surface water (Shrestha, 2001). This is due to fact that the extraction of groundwater to fulfill the demand of growth urbanization is increased and portion of water infiltrating for groundwater is reduced due to increase in imperviousness. Hence rechargeable area of the valley importantly northern groundwater zone should have land use planning providing more open area with less paved.

To control rapid drawdown of groundwater level, excessive extraction of deep groundwater should be controlled providing alternate options such as introducing rainwater harvesting techniques from micro (private) to macro (institutional) level, and water demand management. Riverhead forests surrounding the existing surface sources should be protected so that persistent surface flows could be observed throughout the year.

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