Salinity Status in Groundwater : A study of Selected Upazilas of Southwestern Coastal Region in Bangladesh

Transcription

1 Global Science and Technology Journal Vol. 1. No. 1. July 2013 Issue. Pp Salinity Status in Groundwater : A study of Selected Upazilas of Southwestern Coastal Region in Bangladesh Md. Rezaul Hasan*, Md. Shamsuddin** and A.F.M. Afzal Hossain*** Salinityis a crucial issue in coastal area of Bangladesh. To address the status of groundwater salinity for nine upazilas (sub-district) of southwestern coastal region samples from 272 randomly selected tubewells were considered. Qualitative data were also collected to address social implication of the problem. It reveals that the minimum salinity in shallow aquifer was 51 ppm to 338 ppm and the maximum was 294 ppm to 3751 ppm. About 18% shallow tubewells had salinity more than 1000 ppm against 5.6 % deep tubewells. Although most of the respondents (86.7%) used groundwater but 79% did not perceive increase in salinity. Keywords: Groundwater Salinity, Tubewell, Groundwater Quality Parameters, Sociological Indicators, Peoples Perception Field of Research: Environmental Engineering 1. Introduction Bangladesh, lies in the northeastern part of South Asia, has 710 km coastal line. The coastal area covers about 32% of the country (MoWR 2005). Due to influence of tide and presence of salinity in coastal rivers, the livelihoods of over 50 million inhabitants of coast area depend on groundwater for meeting domestic, municipal, industrial and other needs. As salinity in the groundwater is a key factor, a clear idea of the extent of fresh saline groundwater in various depths is required for optimal development and use of this precious potable water resource. The southwestern coastal region is characterized by the Ganges tidal flood plains with low relief, criss-crossed by rivers, tidal marshes and swamps. Although groundwater is abundant in the region, saline water intrudes into the aquifer system due to reduction of upstream freshwater flow, shrimp farming and over abstraction of groundwater makes the situation worse. Department of Public Health Engineering (DPHE) engaged IWM for conducting a study on salt water intrusion in groundwater in a pilot area of southwestern coastal region. In this context, an initiative has been taken to assess the status of groundwater salinity through hydro-chemical investigation and PRA approach for its extent. Although hydro-chemical investigation reflects fairly the degree of salinity in groundwater, the relevant sociological indicators are also useful in understanding the level of impact of salinity from social perspectives. The boundary of the study area mainly follows existing rivers and is not necessarily *Md. Rezaul Hasan, Senior Specialist, Irrigation Management Division, Institute of Water Modeling (IWM), Dhaka 1206, Bangladesh. mrh@iwmbd.org **Md. Shamsuddin, Senior Specialist, Irrigation Management Division, Institute of Water Modeling (IWM), Dhaka 1206, Bangladesh. mrh@iwmbd.org ***A.F.M. Afzal Hossain, Deputy Executive Director (P&D), IWM, Dhaka 1206, Bangladesh 112

2 congruent with the true administrative boundary. The study area covers nine upazilas of Khulna, Jessore and Satkhira districts with an area about 1534 km 2 (Figure 1). The paper is organized based on water sample analyses of randomly selected water points in the study area. Also qualitative information using PRA technique was adopted to supplement the hydro-chemical investigation. Figure 1: Map showing Study Area 2. Literature Review In Bangladesh, very few studies were undertaken on groundwater salinity aspect. Most of the research works to date have been carried out mainly on irrigation, drainage, flood control and diversion of Ganges flows during the dry season. However, salinity in water is a normal phenomenon in the southwestern coastal region. Based on a survey conducted during 2009, SRDI (2010) reported that about million hectares of new land was affected by various degree of salinity during last 9 years from the year 2000 to 2009 only. Salinity is the measure of concentration of dissolved salts in water such as chloride anions. There are two widely used methods for measuring salinity namely electrical conductivity (unit: mmhos) and chloride concentration (unit: mg/l or parts per million, i.e., ppm). The metric equivalent for mho is Siemens (S), where 1 mmhos/cm = 1 ms/cm = 1000 µs/cm. The recommended range of chloride in drinking water is 150 to 600 ppm 113

3 (ECR, 1997). However, Bangladesh government recommended a higher value upto 1000 ppm for problematic areas including coastal belt (DPHE, 2006). The unconsolidated river borne alluviums and semi-consolidated sedimentary sequences form extensive aquifers over most of Bangladesh. Groundwater can be abstracted from aquifers at varying depths. Aquifers may not be classified in terms of depth where the depth would depend on local/regional hydro-geological conditions (DPHE 2000). There should be an aquitard or aquiclude separating the shallow and deep aquifers. During the last four decades thousands of HTWs were installed all over the country. HASKONING & IWACO (1981) found upper aquifer with brackish to saline water in Khulna region. Based on a comprehensive field data collection, the study reported that the fresh-saline groundwater interface lies at depth between 200 m and 300 m. The chloride contents in the deep aquifers ranging from less than 25 ppm to 100 ppm were found at Dumuria. MPO (1986) based on the information of UNDP(1982) mentioned that sufficient groundwater is available in Khulna region with the transmissivity in the range of 1000 m 2 /day to 2000 m 2 /day in the main aquifer. Sir William Halcrow & Partners Ltd (1993) tried to relate freshwater and groundwater interactions at a conceptual state only. In the upper aquifers the position of the saline fronts can be controlled by regional flow of groundwater towards the sea and prevailing recharge conditions. In addition freshwater lenses may occur overlying the saline water. Under natural conditions only minor seasonal changes take place in these relationships between fresh and saline waters. EGIS (2001) reported groundwater salinity between 40 and 200 m below ground surface in the coastal belt. It was revealed from IWM (2002) study that groundwater level varies from 0 m to 2.0 m above mean sea level in the Khulna region. In general salinity level exists ppm. Similar types of temporal variation of groundwater level and groundwater salinity has been found but no significant spatial variations. 3. Methodology 3.1 Study Design The present study was formulated on the basis of field activities conducted during December, The field activities were carried out from hydro-chemical and social considerations. 3.2 Hydro-chemical Investigation For the present study groundwater samples were collected from shallow hand tubewells (SHTW) and deep hand tubewells (DHTW) with varying screening depths from m and m respectively. The number of tubewells selected from each union (sub-upazila) randomly by consulting the list of tubewells available with DPHE. Total number of tubewells was 272 of which 147 numbers represented SHTW and remaining 125 DHTW. The distribution of tubewells is given in the Table 1. Significant quality parameters of groundwater salinity like ph, temperature, EC, TDS and salinity were measured at each selected tubewells using field test kit. In order to check quality of results given by the field testing kit, 10% water samples have been tested at the DPHE laboratory, Khulna. Prior to the selection of the testing laboratory samples of three wells were tested in Bangladesh University of Engineering and Technology (BUET), Khulna University of Engineering and Technology (KUET) and DPHE, Khulna laboratory. It was found that the DPHE 114

4 laboratory analyses matched satisfactorily to those of BUET results, so DPHE laboratory was selected for carrying out lab analysis. Since field test-kit results do not show a high level of accuracy, the field values were modified according to relations derived from the lab test results. 3.3 Social Survey For collecting pertinent data on social aspect, participatory rapid appraisal (PRA) approach was followed which primarily included focus group discussion (FGD) and key informant interviews (KII). The size of sample household was selected based on random sampling technique. Since most of the groundwater samples were concentrated in six upazilas, household samples were taken from these upazilas using area proportionate method. Here multistage sampling technique was used. The stages of multistage sampling were upazila union mouza/village household. In selecting one union from the six sample upazilas one union was randomly selected. Subsequently one village was selected from each upazila, except Dumuria. For Dumuria two villages were selected due to large sample size. The number of household selected for the study area based on systematic random sampling was 270. The distribution of upazilawise household samples is given in the Table 1. A structured questionnaire was used for the collection of household data. Some data were collected by FGDs and KIIs using checklist. The FGDs were conducted at nine unions with local level public representatives and people of different professional groups (farmers, businessmen, service holders, shopkeepers, teachers, housewives, etc). KIIs were held in five upazilas with Sub Assistant Engineers of DPHE. In addition, the Executive Engineer of DPHE subject to availability was discussed. Table 1: Distribution of Tubewells and Household Samples by Upazila District Upazila No of SHTW No of DHTW No of Sample Households Khulna Dumuria Batiaghata Paikgacha PhulTala Khan Jahan Ali Jessore Abhaynagar Keshabpur Manirampur Satkhira Tala Total Results and Discussions 4.1 Groundwater Quality Parameters in Aquifers The water quality data in respect to the parameters as mentioned above were measured and upper and lower limits of each parameter is given in Table 2. In other words, the characteristics of sample water points collected from SHTW represent for shallow aquifer and similarly those collected from DHTW represent for deep aquifer. A relationship has been developed between lab and field test results with respect to EC, TDS and salinity. The EC and TDS values from field test as well as laboratory 115

5 test match satisfactorily and the relationship curves are shown in the Figure 2 and adopted for the study. Table 2: Variation of Groundwater Quality Parameters in Aquifers Upazila ph Conductivity (µs/cm) Salinity, Cl (ppt) TDS (ppt) SHTW DHTW SHTW DHTW SHTW DHTW SHTW DHTW Dumuria Batiaghata Paikgacha PhulTala Khan Jahan Ali Abhaynagar Keshabpur Manirampur Tala Figure 2: Relationship between Laboratory and Field Test Values for EC and TDS. Lab EC y = 0.647x R² = Field EC The salinity was measured with the Hatch salinometer has some limitations. For low values it showed 0.3 ppt and for higher values it showed some relationship but is also erratic to some extent (Figure 3). The two lines diverge at high value. The samples invariably include sodium chloride and some amount of chlorides of other elements. An attempt was made to convert the field test values to laboratory values as chloride but the relationship curves of different types could not account for very low values. The best fit curve obtained from the equation also does not show consistency for the low values (Figure 4 left). Therefore, an equation given in the right hand side of the Figure 4 has been used to obtain the chloride value measured in the field for lower values. Laboratory TDS y = 7E-05x x R² = Field TDS 116

6 Figure 3: Comparison of Salinity in Laboratory and Field 3000 Salinity in ppm Field Lab Well Code Figure 4: Relationship between Lab Value as Total Chloride and Field value as Chloride in the Upper Range (left) and Lower Range (right) Lab Value as Chloride y = 2E-05x x R² = Field Value as Chloride Lab Value as Chloride y = 0.001x x R² = Field Value as Chloride 4.2 Findings of Salinity Level The minimum salinity varied from ppm for shallow aquifer and was around 300 ppm for deep aquifer in different study upazilas. The maximum value in different upazilas varied from ppm and ppm for shallow and deep aquifers respectively. On the other hand, the minimum salinity for each upazila in shallow aquifer assessed in the form of chloride varied from ppm while the maximum value varied from ppm. Similarly, the minimum value in deep aquifer ranged from ppm while the highest limit ranged from ppm. The summary of different upazilas is given in Table 3. For easy visualization, the salinity distribution maps of shallow and deep aquifers are given in Figure

7 Table 3: Range of Salinity (ppm) in Shallow and Deep Aquifers Upazila Derived Salinity as total Chloride % (>1000 ppm of total Chloride) SHTW DHTW SHTW DHTW Dumuria 67-1, Batiaghata 338-1, Paikgacha 51-3,751 4, * PhulTala 77-1, * 0* Khan Jahan Ali * 0* Abhaynagar * 0* Keshabpur Manirampur Tala Total * Scanty data The salinity in the deep tubewells was mostly within 1000 ppm. Only 5.6 % DHTW had salinity exceeding 1000 ppm. In Paikgacha almost all DHTW had salinity exceeding 1000 ppm. The percentage of that in Tala, Dumuria and Batiaghata were 11.1, 5.41 and 2.27 respectively. In the study area 18.37% SHTWs had salinity exceeding 1000 ppm. It is to be noted that deep tube wells virtually does not exist in Paikgacha as the deep aquifer is not suitable for development of water supply in the upazila. Figure 5: Salinity Distribution Maps for Shallow Aquifer (left) and Deep Aquifer (right) 118

8 4.3 Findings of Household Survey Hasan, Shamsuddin& Hossain As stated a total of 270 households were surveyed for collection and analyses of social data of the study area. Information was collected mainly from the heads of households. But where the heads of households were not available for some reason, the same were collected from other knowledgeable members of the households. Only five females (1.9%) are reported as heads. Out of those, majority of them are illiterate. Most of the male heads (29%) are educated up to primary level. The dominant age group of the heads of households was years which consisted of 35.6 % followed by the age group of years (25.2%). The principal occupation pursued was seen to be farming (24.5%). This is followed by selling labour on daily basis (18.1%). Business occupies third position (17.0%). Moreover, it is observed that annual household income group (BDT 100, ,000) was the dominated group consisted of 24.1% of the total income group. This may be indicated a moderate economic condition of the area. Total population of the sample area was 1205, numbers of male and female are 604 (50.1%) and 601 (49.9%). The average household size of the sample area was 4.5, which is close to the national household size. The literacy rate of the population of more than four years is 86%. Male and female literacy rate is almost same. Most of the population (35%) has got primary education which is followed by 6th to 10th level (34%). Higher education is very marginal. 4.4 Water Facilities It is revealed from the household survey that most of the respondents (86.7%) use groundwater. In Khulna, the rate of DHTW use was 48%. Besides, they use Pond Sand Filter, PSF, (22%) and Very Shallow Shrouded Tubewell, VSST, (22%). Most of the people (98%) of Jessore district use DHTW. In Satkhira, majority (60%) people use VSST which is followed by SHTW (30.0%). As for drinking water source irrespective of district, most of the cases (89%), ownership of the sources belong to government. However, in Satkhira, 55% households use own source for it. In agriculture most of the households (48%) use own source and the next ownership belong to neighbors. On the other hand, non-government organizations (NGO) cover 4% of drinking and 1% of agriculture only. No NGO initiative was found in Jessore. Besides, about 24% of the households only get drinking water source within 50 meters. In Rabi and Kharif-1 seasons, most of the agricultural land cannot be brought under cultivation due to presence of high degree of salinity in water sources. However, the Boro cultivation is limited in the upper part of the study area where suitable ground water is available. Most of the households in Khulna practice surface water irrigation in the upper reach since salinity remains low. Here groundwater is abstracted from shallow aquifer by only 1% households. Hand tube wells are used in the upazilas of Satkhira and Khulna districts for providing minor irrigation to vegetables and minor crops in a very small scale. In Jessore, most of the households practice irrigation for agriculture through tubewells. 119

9 4.5 Impacts of Salinity on Health Hasan, Shamsuddin& Hossain All of the sample households were asked about the water quality of different source they use, 94% respondents opined that their drinking water quality is good. About 79% respondents cannot perceive any increase in salinity in groundwater. About 6% respondents of Khulna and 1% of the Jessore stated that they have salinity in drinking water. But 75% respondents of Satkhira stated for iron contamination. About 14% agricultural water sources in Jessore have salinity; it is 6% in Khulna. But ironcontamination is found in all three districts. A marginal level arsenic contamination is also claimed in Khulna and Satkhira. Information on health condition was collected from the households. The most common diseases that they generally suffer most are the cough and cold (84.4%) followed by Influenza (72.6%) in the sample area. The position of dysentery and diarrhea is almost close; it is 52% and 49% respectively. Local people suffer from diseases like diarrhoea, dysentery, skin diseases etc for taking saline water. 4.6 Findings of FGD and KII Salinity exists in the surface water of the study area since long as the area is linked with the sea through estuaries. But reduction of upland fresh water flow has increased since commissioning of Farakka barrage as well as sedimentation has increased in the river system of the region. Water logging is felt in many places. Salinity in Keshabpur and Tala is increasing from detachment of Kobadak from the Ganges via Mathabhanga. Change in groundwater salinity is not prominently perceived but there is apprehension of increase. It is percieved that salinity is increasing in groundwater in the upazilas, namely Tala, Paikgachha, Abaynagar, Manirampur, Batiaghata, etc., as reported in KII and FGDs. In these upazilas, salinity starts from deep aquifer and increase with the increased depth. In some places in the south suitable deep aquifer is not available. In these places people use shallow tube well for domestic purpose. Shrimp is cultured throughout the area. People consider it highly beneficial and economically viable. Here, at some places, shrimp fields are operated in dry months while the same land is used for paddy in wet months. However, it is almost universally felt that shrimp culture by intruding saline water is degrading the soil quality and poor paddy production. With recent outbreak virus infection in shrimp, people have started shrimp culture with STWs with low saline water. This has done away with the problem of virus infection and paddy production is less affected by low saline water of STWs. 5. Conclusion This paper is an attempt to shed some light on the present status of groundwater salinity in the study area. The assessment was based on the outcomes of the limited data collected during December, 2011 on a pilot basis of Khulna region. The study reveals that groundwater of southwestern coastal region is mostly saline. This is more prominent in the shallow aquifer. It was found that about 18.37% SHTWs had salinity more than 1000 ppm. The salinity in SHTWs in the upazilas of Jessore 120

10 and Satkhira was less than 1000 ppm. The situation was found worse in Paikgacha and Batiaghata upazilas of Khulna. In the study area about 5.6 % DHTWs showed salinity above 1000 ppm. In contrast, almost all DHTWs in Paikgacha exceeded salinity level. The percentage of DHTW containing salinity more than 1000 ppm in the upazilas of Tala, Dumuria and Batiaghata were 11.1, 5.41 and 2.27respectively. Most of the respondents (86.7%) use groundwater, but 79% respondents do not perceive any increase in salinity in groundwater. During Rabi and Kharif-1 seasons, most of the agricultural land could not be cultivated due to presence of high salinity. Moreover, shrimp culture has further deteriorated the coastal fragile eco system. Local people suffer from many diseases like diarrhoea, dysentery, skin diseases, etc. for taking saline water. Demand for potable water is increasing globally day by day to meet domestic, agricultural and industrial needs. But availability of potable groundwater is scarce in the entire coastal belt of Bangladesh which is one of the most vulnerable countries due to climate change effect. Sea level rise due to climate change has made coastal ecosystem more vulnerable in respect of livelihood including natural hazards of frequent cyclone, salinity, erosion, poor sanitation, inadequate potable water supply, etc. In this context protection of potable groundwater is crucial for overall socioeconomic development and existence of the country. Therefore, it is imperative to adopt proper measures immediately to preserve fresh groundwater for saving over 50 million people of the coastal belt of Bangladesh. References DPHE (2000), Deeper Aquifers of Bangladesh A Review. Department of Public Health Engineering (DPHE), Dhaka, Bangladesh DPHE (2006), Development of Deep Aquifer Database and Preliminary Deep Aquifer Map, Final Report, Department of Public Health Engineering (DPHE), Dhaka, Bangladesh. ECR (1997), Environmental Conservation Rules, Bangladesh Gazette. Ministry of Environment and Forest, Government of the People s Republic of Bangladesh. EGIS (2001), Integrated Environment Management, A Case Study on Shrimp-Paddy Landuse Strategies in the Southwest Region. Environment and Geographic Information Services (EGIS) HASKONING and IWACO B.V. (1981), Khulna Water Supply Project - Feasibility Study, Final Report, Vol 3, pp. 67, Department of Public Health Engineering, Dhaka, Bangladesh. IWM (2002), Khulna-Jessore Drainage Rehabilitation Project, Special Monitoring of Rivers and Tidal Basins for Tidal River Management, Final Report, Vol-I, pp. 4-20, Institute of Water Modelling (IWM), Bangladesh Water Development Board. MoWR (2005), Coastal Zone Policy (CZPo), Ministry of Water Resources (MoWR), Government of the People s Republic of Bangladesh. MPO (1986),Technical Report No. 5 on Groundwater Resources, Master Plan of Organization (MPO), Ministry of Water Resources, Government of the People s Republic of Bangladesh. Sir William Halcrow & Partners Ltd et al. (1993), Southwest Area Water Resources Management Project TA No BAN, Land Resources, Agriculture and Fisheries (FAP-4),Final Report, Vol-6, Flood Plan Coordination Organization, 121

11 Ministry of Water Resources, Government of the People s Republic of Bangladesh. SRDI (2010),Saline Soils of Bangladesh, Soil Resource Development Institute (SRDI), SRMAF Project, Ministry of Agriculture, Government of the People s Republic of Bangladesh. UNDP (1982), Ground-Water Survey-The Hydrologic Conditions of Bangladesh, United Nations Development Programme (UNDP), New York, United Nations. 122