Investigation of Fresh Water Cultivation from Vadamaradchy Lagoon: A Case Study of Jaffna District

GRD Journals | Global Research and Development Journal for Engineering | Emerging Research and Innovations in Civil Engineering (ERICE - 2019) | February 2019

e-ISSN: 2455-5703

Investigation of Fresh Water Cultivation from Vadamaradchy Lagoon: A Case Study of Jaffna District 1MH.

Mohammed Suhail 2Rasenthiram Athavan 3Darshan J Mehta 1,2 UG Student 3Assitant Professor 1,2,3 Department of Civil Engineering 1,2,3 DGGEC Surat, Gujarat Abstract

The current state of globalization had increased the demand for ground water due to the growth in the population. In order to be more responsible in protecting the ground water resources various artificial methods had been adopted. The areas located around the Vadamaradchy lagoon in Jaffna peninsula of northern part of Sri Lanka are highly vulnerable to water scarcity and saline ground water issues due to the lack in the proper utilization of available sources. This exploration is concerned on quantitative estimation of storage capacity of Vadamaradchy lagoon and to find the most efficient hydraulic structure which can be easily accessible to solve the salinity of groundwater and to increase the water level in a productive manner of these prone areas. The study area is characterised by an average rainfall of 1298Âą683 mm. The catchment runoff from average rainfall (1298 mm) is 78.72 MCM and from 65% dependability rainfall (1128 mm) is 61.08 MCM. The capacity of ponds and waterways in the catchment area of Vadamaradchy lagoon is 13.66 MCM. Vadamaradchy lagoon is directly receiving 101.25 MCM from average rainfall and 87.99 MCM during 65% dependability rainfall. The lagoon is incapable to store 166.31 MCM and 135.40 MCM of water during average rainfall and 65% dependability rainfall respectively. So, in order to retain the surcharge water, it is necessary to construct 3 m height embankment around lagoon boundary. Annually pond can hold maximum 140.4 MCM of water which can easily satisfy the water requirement (30.66 MCM) of total population.

Keyword- Vadamaradchy Lagoon, Ground Water, Fresh Water Cultivation, Jaffna __________________________________________________________________________________________________

I. INTRODUCTION Various solutions have been considered in different studies to supplement the shortfall in fresh water which has been caused by increasing agricultural activities and contamination of ground water in Jaffna district. Increasement in nitrate, salinity and bacterial levels above the national standards is a tremendous concern necessitating a definite solution immediately. The increasing retrograde quality of ground water disclose the need of possible alternative sources of supply and for preservation. Most of the runoff drains to the sea through the intermittent rives and through lagoons. It has been shown that the salinity of water in underground reservoirs increased when the recharge from the rainfall was reduced. Hence, steps should be taken to increase the recharge to the underground resources by conserving more of the rainwater (Navaratnarajah, 1994). Recharging the ground water reservoir and protecting it from salt-water intrusion are great importance to the existence of Jaffna Peninsula.

II. OBJECTIVES The objective of the study is to store the excess runoff, to improve the ground water quality and to develop a model in Vadamaradchy lagoon.

III. STUDY AREA AND DATA COLLECTION Jaffna Peninsula in northern Sri Lanka has an area of 1036 Sq. Km and an annual mean rainfall of 1298 mm and a population of about 600,000 people of whom only a small fraction is supplied with potable water (http://www.jaffna.dist.gov.lk/index.php/en/).

Jaffna is located in between 9.66150N, 80.02550E (see figure 1). Water Resources development in the Peninsula has been attempted from the time of the Dutch empire over 300 years ago. More lately, the British Govt. Agents starting with Sir William Crofton Twynam in 1879 worked on the conversion of the two internal lagoons namely Vadamaradchy and Upparu to fresh water lakes (Sivakumar, S. S.2013). Though these efforts were abandoned later due to damages to the system during cyclonic weather, some benefits such as cultivating previously abandoned as unsuitable lands and cattle drinking water from the lagoon during dry

All rights reserved by www.grdjournals.com

307

Investigation of Fresh Water Cultivation from Vadamaradchy Lagoon: A Case Study of Jaffna District (GRDJE / CONFERENCE / ERICE - 2019 / 061)

season (Webb, 1943) proved the concept as sound and this project is to develop it further with a little bit of new technology to have a robust system on the ground which is very unlikely to be damaged during extreme weather.

Fig. 1: Map of Vadamaradchy lagoon Source: Land use Department, Jaffna

Jaffna receives 75% of its rainfall between September and December during North-East monsoon each year while most of the rainfall is in November (www.meteo.gov.lk). Vadamaradchy lagoon is located in the interior of the Jaffna peninsula and having the surface area of 78 Sq. Km which is described as brackish to saline lagoon connected to the Indian Ocean by a narrow channel at Thondaimanaru, with an average depth of the lagoon in wet season around 2 m. Vadamaradchy lagoon comprise a catchment area of 298 Sq. Km. Principal vegetation consists of sea grass beds, salt marsh, mangrove swamps, Palmyra and coconut palms, forest scrub rice fields and croplands in the surrounding areas. There are extensive mangroves swamps and sea grass beds in the north-west and south-east part of the lagoon, while extensive mudflats dominate the eastern and western ends. However, surrounding areas of the lagoon are used for agriculture. The figure 2 shows Vadamaradchy lagoon at Thondaimanaru barrage.

Fig. 2: Vadamaradchy lagoon at Thondaimanaru barrage Source: Irrigation Department, Jaffna

A. Methodology In this exploration, analysis is carried out by using Lacy’s formula for estimation of catchment runoff from rainfall. Here Lacy’s formula is used because he has considered monsoon duration factor and catchment class characteristic to calculate the runoff precisely (Lacey, G., 1930).

All rights reserved by www.grdjournals.com

308

Investigation of Fresh Water Cultivation from Vadamaradchy Lagoon: A Case Study of Jaffna District (GRDJE / CONFERENCE / ERICE - 2019 / 061)

R=

P 1+304.8f/PS

(1)

Where R is runoff in cm, P is rainfall in cm, f is monsoon duration factor which is considered as mentioned below 0.50 – very short 1.00 – standard length 1.50 – very long And S is a value dependent on catchment class characteristic as 0.25 – flat, cultivated B.C. soil 0.60 – flat, partly cultivated soil.

1.00 – average 1.70 – hills and plains, little cultivated The preliminary dimensions of low embankment dam up to the height of 4.5 m is shown in table 1 using Strange’s recommendation (Strang G,1973).

Sr. No Design parameters Strange’s recommendation 1 Top width (m) 1.85 2 Upstream side slope (H:V) 2:1 3 Downstream side slope (H:V) 1.5:1 4 Maximum free board (m) 1.2 to 1.5 Table 1: Strange’s recommendation for preliminary dimensions of embankment dam Source: Irrigation engineering and hydraulic structures by SK.Garg

IV. RESULTS AND ANALYSIS Vadamaradchy lagoon receives an average rainfall of 1298 mm and 65% dependability rainfall of 1128 mm during North-East monsoon. The inflow from direct rainfall and catchment runoff (from equation 1) to lagoon are 101.244 MCM and 47.420 MCM respectively. The capacity of ponds and water ways in the surrounding of catchment areas is 13.656 MCM (Department of Agrarian Development- Jaffna). The total inflow to the lagoon without any utilization is 135.405 MCM. Sr. No 1 2 3 4 5 6

Parameters During average rainfall Annual rainfall 1298 mm Direct inflow to the lagoon 101.25 MCM Runoff from catchment area 78.72 MCM Capacity of ponds and waterways in catchment area 13.66 MCM Runoff to the lagoon 65.07 MCM Total inflow to the lagoon 166.31 MCM Table 2: Summary of result analysis

During 65% dependability rainfall 1128 mm 87.99 MCM 61.08 MCM 13.66 MCM 47.44 MCM 135.41 MCM

To hold the unused water flowing in to the lagoon, maximum hydraulic height of embankment during average annual rainfall and 65% dependability rainfall are 2.13 m and 1.74 m respectively needed. Figure 3 shows the cross section of embankment having base width of 12.35 m, top width of 1.85 m, hydraulic height (HFL) of 1.8 m, free board of 1.2 m, total height above lagoon bed level is 3 m. The upstream side slope and downstream side slope are 2:1 and 1.5:1 respectively (Spencer E, 1967).

Fig. 3: Cross section of embankment with dimensions (in mm)

V. CONCLUSION The present study of Vadamaradchy lagoon reveals the preliminary dimensions (see figure 2) of the low embankment from Strange’s recommendation. Therefore, the hydraulic height of embankment is chosen as 1.8 m from 65% dependability rainfall.

From Strange’s recommendation maximum freeboard of 1.2 m is provided, top width 1.85 m, upstream side slope 2:1 (H:V),

All rights reserved by www.grdjournals.com

309

Investigation of Fresh Water Cultivation from Vadamaradchy Lagoon: A Case Study of Jaffna District (GRDJE / CONFERENCE / ERICE - 2019 / 061)

downstream side slope 1.5:1 (H:V). For this above dimension we can store a maximum 140.4 MCM of water up to a rainfall of 1281 mm (65% dependability rainfall). Vadamaradchy lagoon in the Jaffna Peninsula have sufficient resources to meet the water demand of 30.66 MCM of whole population and above proposed model of embankment will prevent the intrusion of stored water in lagoon to the low-lying areas like Idaikadu and Tampalai moreover, it can be easily accessible way to solve the salinity of groundwater and to increase the water level in a productive manner of these prone areas like Karaveddy, Kapoothu and Mandan.

REFERENCES [1] Department of Agrarian Development- Jaffna.

[2] District secretariat, Jaffna. http://www.jaffna.dist.gov.lk/index.php/en/ [3] Janen, S. S., & Sivakumar, S. S. (2014). Ground Water Quality Improvement of Jaffna Peninsula of Sri Lanka by Regulating Water flow in the lagoon Mouths. International Journal of Scientific & Engineering Research, Vol. 5, 973-978.

[4] Lacey, G., (1930). Stable channels in alluvium. Minutes Proc., Inst. Civ. Engrs, Lond. 229, 259–292.

[5] Metrological Department of Sri Lanka. (2012). Climate in Sri Lanka. Retrieved from Metrological Department: www.meteo.gov.lk [6] Navaratnarajah, V. (1994). Water Problems in the Jaffna Peninsula. Affordable Water Supply and Sanitation, Proceedings of the 20th WEDC Conference. Colombo, Sri Lanka: WEDC Loughborough, UK. [7] Sivakumar, S. S. (2013). Reclamation of Land and Improve Water Productivity of Jaffna Peninsula of Northern Sri Lanka by improving the water quality of the lagoons. Irrigation Department.

[8] Spencer E (1967) A method of analysis of the stability of embankments assuming parallel inter-slice forces. Geotechnique 15:11– 26.

[9] Strang G, Fix J (1973) An analysis of the finite element method. Prentice-Hall, Englewood Cliffs.

All rights reserved by www.grdjournals.com

310