Thesis of master degree: Numerical simulation for the assessment of groundwater safe yield in red river delta, Viet Nam

In Red River Delta, there are many important economic regions located on the

coastal areas The growth of both the economy and the population in these areas during the last decades, which is based on the availability of water resources, and the extensive exploitation have strongly increased the pressure on this finite and vulnerable resource Since surface water is unevenly distributed and increasingly affected by human activities, groundwater has become the major source of potable water.

This thesis therefore focused on contributing to the improvement of groundwater management in RRD by determining groundwater safe yield using modelling method Nam Dinh Province was selected to be the study area.

In the northern areas of Nam Dinh Province, due to the the high concentration of

contamination in the groundwater aquifers, surface water is used as the main source of water for the region Groundwater usage in these areas is mainly for other purposes than domestic use Small scale groundwater extraction can be found near the main rivers with shallow wells in the uppermost aquifer due to the high level of contamination Deeper aquifers are the main subject for extensive extraction in the province Significant extractions are found in the south of Nam Dinh, where large freshwater lens in Pleistocene aquifer are located Therefore in this thesis, the

Pleistocene aquifer is the main area of interest.

It was decided to use the Visual MODFLOW for the setting up of a numerical model of the Nam Dinh Area The 3D hydrogeological structure for the model was created from strata data of 83 boreholes, including 27 boreholes from Nam Dinh, 15 boreholes from Ha Nam, 17 boreholes from Ninh Binh, 23 boreholes from Thai

Binh and | from Thanh Hoa Natural neighbors method was used to interpolate the

elevation of surface and bottom of the layers.

The 3D structural model was built with 5 layers, representing 4 aquifers and 1aquitard, including Upper Holocene aquifer (qh2), Lower Holocene aquifer (gh1),Pleistocene aquitard (qp2), Pleistocene aquifer (qpl) and Neogen aquifer (n) with

the order from top to botlom respectively The finite difference grid used for the model has the size of 181 x 160 (181 columns x 160 rows, the size of each cell is approximate 400m x 400m).

Observed water heads from 19 wells were used to calibrate and verify the model The normalize root mean squared of the calibrated model is 6.296%, which is considered to be good enough to simulate the future uses of groundwater for the

study area

‘To show the impacts of groundwater utilization on the qp aquifer in Nam Dinh Province, enarios of future situations were simulated using the calibrated model

Extraction rates were extrapolated until 2050 and three versions were considered: 1) Extraction rises constantly until 2050 in the same manner than from 1994 to 2012; 2) Extraction stays on a 2012 level, which means that no additional water is going to be extracted; 3) Extraction gradually declines to 0 by 2050.

‘The simulation results of these scenarios were used to estimate the groundwater safe yield for Nam Dinh Province It showed that the safe yield for the area is

estimated to be 70300 m'/day

1 hereby certify that the work which is being presented in this thesis entitled, ‘Numerical simulation for the assessment of groundwater safe yield in Red iver Delta, Viet Nam” in partial fulfillment of the requirement for the award of the Master of Science in Integrated Water Resource Management, is an authentic record of my own work carried out under supervision of Associate Professor Dr Vu Minh Cat and Dr Bui Du Duong.

‘The matter embodied in this thesis has not been submitted by me for the award

of any other degrees or diplomas,

Date: 28 November 2014

ACKNOWLEDGEM NTS

This thesis was completed at Faculty of Water Resources Engineering, Thuy Loi University.

First and foremost, I would like to thank my advisor, Assoc Prof Dr Vu Minh Cat for his invaluable guidance Ï am deeply grateful that I had the opportunity to learn from his knowledge.

1 would like to thank Dr Bui Du Duong for his helpful contribution to the hydrogeology field and his supervision of my study.

Tam very grateful to Assoc Prof Dr Pham Quy Nhan, MSe, Dang Tran Trung

and MSc Tran Thanh Le for their valuable advices and help with the preparation of

spreadsheet data for the boreholes and well logs.

‘To Ms Mariette van Tilburg, I am very thankful for the English corrections, suggestions for my thesis and for providing me useful writing resources.

Lastly, a word of thanks is extended (o NICHE-VNM-106 project team for providing a 18 months MSc scholarship.

Again, I would like to express my sincere gratitude for all these valuable help!

Objective & scope of study

1.3 Previous studies & state of knowledge 13.1, Inthe world

132 In VietNam 1.4 Methodology

LS Structure of thesis

CHAPTER II - CHARACTERISTICS OF NAM DINH PROVINCE 2.1, Physical settings of Nam Dinh Province

2.1.1, Geographical location 2.1.2 Topography

2.1.3, Climate conditions 2.14, Surface water bodies 2.1.5 Soils and land use

2.1.6, Population & Socio-Eeonomy

2.1.7, Water supply and groundwater utilization 2.2 Geological characteristics of study area

2.2.1, Structural characte ties 2.2.2 Stratigraphy characteristics 2.3, Hydrogeological characteristics

2.3.1 Hydrogeological units

2.3.2 Groundwater dynami 39 2.3.3 Groundwater salinity 4 CHAPTER II - CONSTRUCTION OF NUMERICAL MODEL TO ASSESS GROUNDWATER SAFE YIELD IN NAM DINH PROVINCE 44 3.1, Introduction of MODFLOW model 44

4.1.1, Extraction rises constantly 66 4.1.2 Extraction remains constant 67 4.1.3 Extraction gradually reduces 6 4.1.4, Estimation of groundwater safe yield 70 4.2, Discussion of model results 72 CONCLUSIONS AND RECOMMENDATIONS 74

REFERENCES 16

APPENDICES 8

LIST OF ABBREVIATIONS Generral abbreviations

MONRE Ministry of Natural Resources and Environment NAWAPL National Center for Water Resources Planning and

NDWRPI Nonhem Division of the National Center for Water Resources Planning and Investigation

N,S.E,W North, South, East, West

RRD Red River Delta

UNICEF United Nations International Children’s Emergency Fund ‘Technical abbraviations

mbgl Meter below ground level man Meter above modem sea level

‘TDs otal dissolved solids (mg/L)

LIST OF FIGURES.

Figure 1.1; Steps of study, 19 Figure 2.1: The outline map of Nam Dinh Province 21 Figure 22: Monthly averaged data for temperature, precipitation and potential evaporation in period from 1959 to 2007, measured at Van Ly station, coastal area of Nam Dịnh 23 Figure 2.3: Land use distribution in Nam Dinh province, status 2007, 35 Figure 2.4: Bar chart showing official data for communal and private water supply (ws) in

Nam Dinh from 2005 to 2009 27

Figure 2.5: Quaternary geology and topography of the Red River delta and adjacent

areas (Source: Tanabe et al 2006) 29 Figure 2.6: Geological Sketch map including major struct

boundarie of the Holocene, Pleistocene and Neogene sediments (Source: NAWAPD 30

features and basis

Figure 2.7: Sketch map showing location (orange line) of typical hydrogeoloại ‘ross section of Nam Dinh Province 31

‘gure 2.8: Cross section from Vu Ban to Hai Hau (140x vertical exaggeration,

modified after Hoe et al., 2003) 31

Figure 29: Time-series of monthly averaged Groundwater level of Holocene (gh),

Pleistocene (qp) and Neogene (n) aquifers 41 Figure 2.10: Contour map ofthe hydraulic groundwater heads (m asl) in Pleistocene (qpl) aquifer in the Nam Dinh province in May 2010 (eft) and November 2010 (right) (Source:

NDWRPD, 41

Figure 2.11: Salinity distribution map (TDS) in qp pore water 43

Figure 3.1: Three-dimensiomal finite difference grid used in MODFLOW 45

Figure 3.2: Sketch map showing locations of boreholes used to construct the 3D structural model 48

te 3.3: Finite difference grid and extent border of the model 48 Figure 3.4: 3D hydrogeological structure of Nam Dinh Province 49

Figure 3.5: Sketch map showing bottom elevation contours of Š layers: a) Upper Holocene aquifer, b) Lower Holocene aquifer, e) Pleistocene aquitard, 6)

Pleistocene aquifer, e) Neogen aquifer 52 Figure 3.6: Hydraulic conductivity (m/day) for each aquifer: a) Upper Holocene, b) Lower Holocene, c) Upper Pleistocene, đ) Lower Pleistoce! €) Neogene 3 Figure 3.7: Distribution of aificial well locations in study area sẽ Figure 3.8: Estimated groundwater withdrawal rat from 1994 to 2009 in Nam Dinh

Province 59

Figure 3.9: Sketch map showing the locatio

Nam Dinh Province 6

of groundwater monitoring wells in

Figure 3.10: Calculated versus measured water heads in Q108, 109 and 110 62 Figure 3.11: Best fit simulation water level contour in qp aquifer (December 2012)

63 Figure 3.12: Calibration residuals histogram 63

‘igure 3.13: Calculated versus measured water heads in Q221-Q229 from 2010 to

2012 `

Figure 3.14: Scattered plot showing the relation between calculated and observed head 65 Figure 4.1: Estimated groundwater level until 2050 at Q109 with a constant rise of extraction as postulated until 2012 66 Figure 4.2: Sketch map showing the groundwater level contour in qp aquifer in December 2050 with a constant rise of extraction as postulated until2012 67 Figure 4.3 stimated groundwater level until 2050 at Q109 with a constant level of

extraction as in 2012 68 Figure 4.4: Sketch map showing the groundwater level contour in qp aquifer in December 2050 with a constant level of extraction as 2012 68 Figure 4.5: Bstimated groundwater level until 2050 at Q109 with a constant decline of extraction, 69

Figure 4.6: Sketch map showing the groundwater level contour in qp aquifer in December 2050 with a constant decline of extraction 70 Figure 4.7: Estimated groundwater level until 2050 at Q109 in different scenario 72

LIST OF TABLES

‘Table 2.1: Stratigraphy and Hydrostratigraphy ofthe strata in the Nam Dinh area, 32 ‘Table 3.1: Amount of water wells in Nam Dinh in 1999 and 2009 sr ible 3.2: Table for statistic parameters of calibrated model result 65 ‘Table 4.1: Estimated safe pumping rate in Nam Dinh Province n

CHAPTER I~INTRODUC' ION 1.1 Background information

In Red River Delta, there are many important economic regions located on the coastal areas The growth of both the economy and the population in these areas during the last decades, which is based on the availability of water resources, and the extensive exploitation have strongly increased the pressure on this finite and vulnerable resource, Since surface water is unevenly distributed and increasingly affected by human activities, groundwater has become the major source of potable water"

Understanding and quantifying groundwater resources, especially in coastal areas, is a very complex and difficult task, considerably more problematic and uncertain than surface water hydrology Various studies have been conducted using điiferent types of models, including empirical, probabilistic and deterministic models, Since empirical models are limited in scope and probabil ie models require large data sets and cannot be used to solve many problems in practice (e.g

effects of a future pumping) ''”, numerical deterministic models are increasingly

applied, especially within GIS environments However, in contrast to the developed

‘countries (e.g., Europe, Australia, Japan, and North America), where a vast majority

of projects ave been carried out due to the availability of a wide range of

information and where technical and financial resources are available“), few

projects have been in Viet Nam with very limited results This has led tô an inadequate understanding of the aquifer system characteristics as well as to unwise

groundwater management in Viet Nam, especially in RRD.

‘This thesis therefore focused on contributing to the improvement of groundwater management in RRD by determining groundwater safe yield using modelling method, However, within the limited time, it is not feasible to construct the model for the whole Delta In this study, Nam Dinh Province was selected to be the case

study There are 3 reasons for this selection:

© Nam Dinh province is located in the south of the Red River flood plain In

general, the physical settings of the province are quite in common with that

of the Red River Delta: 1) Adjacent to the ocean in the SE border; 2) The SW border is where clastic sediments of the Cenozoic meet the Mesozoic graben shoulders of the elongated Red River graben; and 3) Agriculture ‘dominated land use with an extensive system of dykes and canals constructed to itrigate the paddy fields with river water

« Nam Dinh Province is facing the same groundwater problems with RRD, including: 1) Continuous declining of groundwater tables on a regional scale; 2) Potential salinization of coastal groundwater resources by seawater intrusion; 3) Potential pollution by unsuitable handling of domestic, agricultural and industrial waste, waste water and sewage; and 4) Unwise management and inadequate understanding of the aquifer system characteristics leaded to serious problems, such as the drying up of shallow wells, land subsidence, ete

‘© Nam Dinh is the province which has the highest groundwater drawdown rate

‘compare to the other provinces/cities in Red River Delta

(For more details, see Chapter 2)

Nam Dinh Province is principally endowed with a subtropical climate and abundant surface water resources, However, economic and social developments,

‘combined with the population growth over the last decades, have strongly increased

pressure on available water resources Surface water is the traditional water source and still used in Northern and Eastern areas of Nam Dinh In South and West of Nam Dinh deeper groundwater resources has been increasingly exploited for domestic as well as economic utilization.

ded Monitoring data since 1995 showed that the groundwater extraction e)

Is in Pleistocene and the recharge resulting in drawdown of groundwater le

Neogene aquifers up to 0.6 myear, A regional abstraction cone has developed in

Pleistocene as well as the underlying Neogene aquifer In this area, the natural

coastward directed groundwater flow has tumed towards the centre of the abstraction cone with horizontal apparent veloci of 0.6 m/year This results in migration of brackish and saline groundwater from East of Nam Dinh as well as from the ocean towards the fresh groundwater area The consequences are that nowadays hand pumps must be replaced by electric pumps in order to pump the ‘groundwater to the surface and, thus, increasing the costs for water supply.

Groundwater will be increasingly important for Nam Dinh’s future water supply

strategy, since surface water is vulnerable and increasingly affected by climate sustainable change, untreated sewage water and industrial waste water, Thus,

‘groundwater exploitation and management is crucial for life, development and the

‘environment in Nam Dinh

1.2 Objective & scope of study

‘The overall goal ofthis thesis isto provide a rough assessment on the safe yield ‘of groundwater for Nam Dinh Province on the basis of numerical modeling method ‘To achieve the overall goal ofthe research, these following specific objectives have been addressed!

+ Clarify the spatial characteristics of groundwater in Nam Dinh

+ Investigate the impacts of pumping activities on the flows and hydraulic heads of groundwater in Nam Dinh

+ Roughly estimate the safe groundwater yield for Nam Dinh,

+ Proposing recommendations to improve groundwater management for the province by analyzing the simulation results

In the northern areas of Nam Dinh Province, due to te the high concentration of ‘contamination in the groundwater aquifers, surface water is used as the main source ‘of water for the region, Groundwater usage in these areas is mainly for other purposes than domestic use Small seale groundwater extraction can be Found near the main rivers with shallow wells in the uppermost aquifer due to the high level of ‘contamination Deeper aquifers are the main subject for extensive extraction in the province Significant extractions are found in the south of Nam Dinh, where large

freshwater lens in Pleistocene aquifer are located Therefore in this study, the Pleistocene aquifer was lected as the main area of interest This study examines cena groundwater-related items in great details for the whole province, in which, ‘groundwater pollution and salinization process were not taken into account due to the limitation of time and collected data, Furthermore, detailed evaluation of alternative groundwater management strategies was also included in this research 1.3 Previous studies & state of knowledge

1.3.1 In the world

Worldwide applying of modelling methods to study the subjects of groundwater

e the former

began in the 19th century, especially in industrialized countries il Soviet Union (Russia and others Republic countries now), the US, France, Denmark History of groundwater modelling can be divided into two stages

“The first stage lasted from the 19th century to the late 50s ofthe 20th century At this stage, modelling method was applied to study the basie seepage problem Several laboratories, which studied soil permeability, were formed in the Sovis Union as VNHG, VODGEO, MGRI This stage is characterized by a strong development of EGDA method (Analogue EGDA), which was developed and used predict groundwater dynamics, balance of groundwater in irrigated areas in Davogia, Dovongie, North Keprad, Central Asia, Ukraine.

‘The second stage extended from the 60s of the 20th century to the present In this stage, modelling method was strongly developed and applied to interpret many complex problems as: Assessment of exploitable re serves of underground wate

Prediction of groundwater dynam in irrigated areas, ete Developed countries like the United States, Russia (former USSR), Denmark, Canada, Australia have used numerical models to serve the integrated management of water resources, Countries in Asia, Southeast Asia have also applied the model to assess and manage water resources in their territory.

For the last decades, several methodologies for groundwater management and vulnerability a ‘sment have been developed to deal with groundwater problems.

‘These issues include: groundwater depletion, groundwater contamination, land subsidence, and seawater intrusion

‘Thomsen et al (2004) presented a highly advanced approach which included spatially dense geophysical/hydrogeological mapping, dense perforation grids as well as numerical modelling, GIS and advanced database technology for

‘groundwater management and protection in Denmark Í”_ Other advanced

approaches include quantitative aquifer modelling for entire catchment areas using numerical groundwater flow modelling as a basis for sustainable aquifer

nent" However, in contrast to the

exploitation and vulnerability a

availability of data in developed countries, the reduced availability of the necessary input data in developing countries require that a significant part of the basic input variables has to be estimated, As ä result, these approaches lean towards a growing

uncertainty "!

13.2 In Viet Nam

In Vietnam, several studies have dealt with groundwater problems Minh, (2004)

used weak Galerkin finite element method to simulate the movement of saltwater

wedges into the coastal aquifer in Hoa Khanh, Tien Giang '"", Postma’s research in

2007 under the Danida Enreca Project provided a set of sources as well as

rmitigations for arsenic contamination in the groundwater of the Red River Delta "''

Nguyen (2011) used finite element modelling for the assessment of seawater intrusion into the ground aquifer in Thai Binh province, Erban (2013) provided an extensive study on arsenic releasing into deep groundwater in the Mekong Delta,

which is linked to pumping-induced land subsidence However, there has been

less improvement in groundwater management in Vietnam, since groundwater problems were still reported to happen in many areas of Vietnam according to

MONRE, 2013 '9

Previous studies in Nam Dinh Province:

Since the 1990s, groundwater resources in the Red River Delta (RRD) including Nam Dinh area were subject of mapping and exploration projects carried out by

{governmental authorities Moreover, Vietnamese universities have published several scientific sudies about groundwater related issues in Nam Dinh and upstream areas, partly in cooperation with international partners The most relevant studies and information sources ate namely

“Characteristics of geology, natural resources and geochemical environment of sediment on tidal estuary of Xuan Thuy and Nghia Hung, Ha Nam Province” report by staffs at Hanoi University of Mining and Geology, 1995.

"Geological mapping for Nam Dinh area ratio 1:50,000" ~ project by Division

47 of Hydrogeology ~ Geology Engineering, 1996 In this project, 27 boreholes

were drilled, including 8 boreholes in Holocene aquifer (qh), 17 boreholes in Pleistocene aquifer (qp) and 2 boreholes in Neogene aquifer (n) Strata data collected from the boreholes was used for the mapping process Slug tests were also conducted in 26 boreholes to determine the hydrogeological parameters of the

aquifers and the chemical composition of water !'.

"Planning of water supply and sanitation in Nam Dinh province in 1999 ~ 2010

period” ~ report by the Center for Water and Sanitation, Nam Dinh Department of

Agriculture and Rural Development, 1999.

"Assessment of groundwater potential and prediction of depletion and salinity instrusion in Hai Hau ~ Giao Thuy, coastal areas of Nam Ding Province” ~ report by the Department of Water Management and Irrigation Works, Ministry of Agriculture and Rural Development, 2000,

"Evaluation on characte tics of natural conditions and non-biological resourc

in coastal areas of Nam Dinh province” — report by Marine Natural Resources &

Environment Survey Center, 2001

"Assessing the sustainability of the exploitation of groundwater resources in Vietnam territory Stra cgic orientation for rational utilization and protection of

groundwater resources by 2020" ~ state project by Bui Hoc et al, 2003 !"!

jeneral survey of groundwater resources in Nam Dinh province: planning for

report by Doan Van Canh and Le Thi Lai, 2003 1

rational and sustainable uses

Research and application of combinatorial methods of geology geophysics numerical modelling to im gate, assess salinity intrusion and search for fresh groundwater lenses or aquifers in coastal areas of Nam Dinh

Van Dan - NDWRPI, 2009 “!

report by Nguyen

In 2010, within the framework of the project “Improvement of Groundwater Protection in Viet Nam" in Nam Dinh Province, 10 additional groundwater monitoring points were constructed, In {otal of 23 new monitoring wells, there are 4 wells in Holocene aquifer, 14 wells in Pleistocene aquifer, 4 wells in Neogene aquifer, and 1 well in Triassic aquifer Slug tests were conducted in 2011 by National Center for Water Resources Planning and Investigation (NAWAPI) to ‘determine the hydrogeological parameters of the Pleistocene aquifer in Nam Dinh Province.

Many of these documents have proven to be very useful secondary data sources Which contributed vast important information for the construction, calibration and validation of the model (see Chapter 3)

1.4, Methodology

Based on principle of water balance this research used the water balance ‘equation to determine the groundwater safe yield, Numerical simulation of a hypothetical case was used to demonstrate the natural groundwater balance, effects of pumping and the dynamic development of the capture.

In this thesis as a systematic evaluation tool for groundwater flow, GIS program and the groundwater modeling program MODFLOW were integrated and used (Figure 1).

At firs, related information available in print or published on the internet were gathered and analyzed To simulate the groundwater flow, regional hydroseolosy, topography hydrology, soil, land use and well data during the period of 1995-2012 were collected from NAWAPI under the Ministry of Natural Resources and Environment (MONRE), Vietnam, The aquifer system was identified and ‘characterized to construct the 3D structural model.

Groundwater safe yield

determination & assessment

Figure 1.1: Steps of study

In order to use MODFLOW, initial conditions, hydraulic properties, and stresses were specified for every model cell in the finite-difference grid Measured heads from the field were assigned directly to inland eonstant-head boundaries.

After setting up the model as well as calibrating and verifying, different pumping schemes were used, based on which, corresponded simulations were executed The results were analyzed (o determine groundwater safe yield for different areas of Nam Dinh Province Finally, recommendations were given to Improve the groundwater management in the area,

LS Structure of thesis

This thesis cons of 4 chapters:

Chapter I - Introduction: This chapter is the introduction which contains the background, importance, objectives of the study and short description of the study area, A comprehensive review of literature and a description of study scope were also presented in this chapter.

Chapter I - Characteristics of Nam Dinh Province: This chapter provides a

‘comprehensive description on the natural conditions as well as socio-economic

ibes the current status of characteristics of the study area This chapter also des

‘groundwater and the utilization of groundwater in Nam Dinh Province.

Chapter IIL - Construction of numerical model to assess groundwater safe ‘yield in nam dinh province: In this chapter, the numerical model s up will be presented The simulation results will then be analyzed to estimate the impacts of pumping activities on groundwater flow and hydraulic head.

Chapter IV - Simulated results and recommendations: ‘This chapter presents the results of several pumping variations Finally, overall conclusions, recommendations were given for improving groundwater management in the study area as well as possible works for the future studies.

CHAPTER II — CHARACTERISTICS OF NAM ĐINH PROVINCE

2.1 Physical settings of Nam Dinh Province

2.1.1 Geographical location

Nam Dinh is the province in the Red River Delta region of northern Viet Nam It

thay a border adjacent to Ha Nam Province to the north, Thai Binh Province to the cast, Ninh Binh Province to the west and East Sea (South China Sea) to the

south-‘east The province has a NW-SE extension of 46 km and a SW-NE extension

‘of minimum 16 km in the central part and maximum 60 km at the coastline to the

Gulf of Tonkin and an area of about 1652 km”, The province comprises one city

(Nam Định city) and nine districts (Giao Thuy, Hai Hau, My Loc, Nam Truc, Nghia

Hung, Truc Ninh, Vu Ban, Xuan Truong, Y Yen) (see Figure 2.1).

Nam Dinh represents the southernmost edge of the RRD, which is located on the western coast of the Gulf of Tonkin, Therefore, its physical seting is connected to the subsidence of the Red River basin and development of the dela

2.1.2 Topography

Nam Dinh terrain is relatively flat; tend to lower from NW to SE with ‘common elevation from Om to 6m The province can be divided into two main

The low-lying delta region - Vu Ban District, Y Yen District, Nam True

District, Truc Ninh District, Xuan Truong District and Nam Dinh city This region is characterized by flat plains with favorable conditions for a high development level of agriculture textile and manufacturing industries

The lowland coastal region - is home to distri such as, Giao Thuy, Hai Hau, and Nghĩa Hung This region has a relatively flat terrain with a coastline of 72 km long, which stuaries of Ba Lat (Red River), Day (Day River), Lach Giang (Ninh Co River) and Ha Lan (So River).

heavily divided by the large

‘The coastal plains, with fertile land, have favorable conditions for raising livestock and fishing ‘This region also locates Xuan Thuy National Nature Reserve

2.13 Climate conditions

The northern part of Vietnam has subtropical monsoon climate, with humidity averaging 84% throughout the year This typical North Vietnamese climate dominates the microclimate of Nam Dinh province with bit cooler temperatures and a higher humidity due to its vicinity tothe s

During the winter or dry season (November - April), the monsoon winds usually blow from the NE along the China coast and across the Gulf of Tonkin, picking up considerable moisture Consequently the winter season in most parts of the country is relatively dry in comparison to the rainy or summer season Lowest daily average temperatures are met in January and February with 10 to

13oC and average humidity can be “relatively low” with 94%

(November-December), but also reach highest average humidity with up to 98%

(January-March) The monthly average rainfall varies between 25 and 220 mm.

‘The summer monsoon from May to October is associated with hot temperatures and heavy rain falls, Maximum daily average air temperature ‘occurs generally in June and July varying from 29 - 31.20C The lowest relative humidity is 86.5% and the highest relative humidity is up to 92% in July, while the monthly average rainfall lies between 175 and 330 mm (Figure 2.2).

‘The climate data from Van Ly station close to the sea shows the development

of the potential evaporation throughout the year Where open surface bodies,

such as channels or irrigated paddy fields exist, the evaporation is quite intense

throughout the year In other areas, evaporation is limited in the dry season (November ~April) by lower rainfall.

Figure 2.2: Monthly averaged data for temperature, precipitation and potential evaporation

in period from 1959 to 2007, measured at Van Ly station, coastal area of Nam Dinh

The total number of hours of sunlight per year averages out about 1650-1700

hours Additionally, being next to the Gulf of Tonkin, Nam Định is normally

affected by tropical storms and monsoons, with an average of 4-6 attacks per

year

214, Surface water bodies

‘The hydrologic network is very dense, including more than 16 small and two main river systems (the Red River and Day River systems) with density of 1.5 km/km’, occupying 3 percent of the natural land area The channel network is increasing in density towards the coastal Nam Dinh area and has crucial relevance for irrigation of paddy fields and other agricultural areas with river water as well as discharge of sewage and waste waters to the sea Four major rivers are located within or at the border of Nam Dinh, the Red River along the NW border of Nam Dinh with its river mouth at the Ba Lat tary, the Dao River connecting the Red and the Day Rivers (SW border of Nam Dinh) and the Ninh Co River with its river mouth to the sea at Lach C

“The Red River is the natural border flow between Nam Dinh and Thai Bình Province The Red River bed has $4 km lengths and is estimated to be 400-500

ing estuary,

mm wide and about 10-15 m deep The water discharge of the Red River varies strongly in terms of the season, The discharge at Ha Noi station reaches a

maximum in July-August (about 23,000 m’/s) and a minimum during the dry season in January to May with typical flow of 700 m’Vs During dry season and.

tidal high stand, elevated salinity has been observed up to 4.5-5 km inland from the Ba Lat estuary.

‘The Day River is a tributary of the Red River, which flows from NW to SE,

winding in a W shape along the SW border of the study area for about 70 km.

before flowing to the ocean Maximum flow rate has been observed in August

with 3110 mỖ/S; lowest flow rate can be almost zero (no flow) in December and January, yearly average is 813 m/s Although this river is tidal influenced,

salinity monitoring has shown that total salinity is generally <Ig/l Day River is considered (o be the western natural boundary of the fresh water lens in the southern coastal districts of the province.

‘The Dao River, with the length and the average width of about 35 km and 500m correspondingly, is one of the major rivers in the region The river

originates from the Red River to the north of Tan De Bridge, flowing through the

ity of Nam Dinh to The Day River in Nehia Minh commune before joining the

‘The Ninh Co River is a tributary of the Red River, located near the center of the southern districts of Nam Dinh The river originates from the north of Xuan ‘Truong district (Hanh Thien commune), flowing through Lac Quan to the South before discharging to the ocean at the Lach Giang estuary, The river is very winding with the average width of 400-500m and extimated length of 35-40 km 215 Soils and land use

‘The soils of the RRD are generally fertile and have been utilized since ancient times for intense agriculture with predominance of rice paddy cultivation, ‘Traditionally, the repetitive flooding events regularly added nutrient rich silt and clay to large areas of RRD Dykes and other flood prevention measures result in the increasing use of chemical fertilizers Large areas of the RRD including Nam Dinh, province are covered with alluvial fluvisols, moreover with saline soils and acid

sulphate soils

Figure 2.3: Land use distibution in Nam Dinh provinee, status 2007.

Nam Dinh is an agricultural dominated province More than 5896 of the whole area 'overed by paddy rice Fish and shrimp aquaculture using fresh and brackish water is widespread with almost 5% area coverage Other annual crops have only less than 2% coverage, Urban and village area represent about 16% of the total area Figure 2.3) In total about 74% of the province area is temporarily flooded by paddy irrigation, aquaculture farming and other water bodies which are expected to have relevant impact for the subsurface water balance.

2.1.6 Population & Socio-Economy

Latest stat ical data published by Nam Dinh province state a total population of

1,826,300 (2009) persons and a population density of 1,105 persons per km” About

16 percent of population live in Nam Dinh city and 84 percent of remain population

live in 9 other districts with an average population density of <1000/ km’ Since

2005, the fertility rate is reported to be quite stable within 15-16 %, corresponding,

to a mortality rate of 5.8 Yo The Viet people represent by far the majority of

population in Nam Dinh, only less than one per cent belong to 3 other minorities, the Tay, the Muong and the Hoa

During the French occupation, the province was famous for textile industry and manufacture Recently, Nam Dinh has established 7 industrial zones which are located along the main roads and ports These industrial zones accelerate the economic development of Nam Dinh and have an enormous need of natural resources such as fresh water and waste water disposal, Therefore, the industrial zones enormously increase the pressure to the environment given the fact that water

consumption as well as waste water treatment and disposal is not sufficiently

2.1.7 Water supply and groundwater utilization

Official statistical data about centralized water supply demonstrate the increasing water demand in Nam Dinh province (Figure 2.4), in both communal as

well as private water supply, The majority of the communal water supply is based

‘on surface water using simple treatment techniques The private households often

take their water from tube wells sereened in 50 to 130 m depths.

160001400012000

‘Total water supply (1000 m3/y)

Figure 2.4: Bar chart showing official data for communal and private water supply (WS) in Nam Dinh from 2005 to 2009

Currently, there are 3 water supply systems in Nam Dinh city: an old system operated since 1924 and the two other systems constructed by the French

‘government Total capacity of three water supply systems is around 50,000 m'/day

using water from surface rivers in the region, According to 2009 statistics, these

systems have supplied freshwater for 24960 households, 365 offices, factories and

83 public taps with the coverage of 92% According to the Provincial Health Center,

the water quality is quite meets the standards,

In rural areas, centralized water supply is very limited due to the difficulties in ‘capital rí ing for creating new connections There are two options for water supply in these areas:

+ Water supply systems in communal scale with the average capacity of

600-1800 m'/day The water here is mainly taken from surfaces water sources Acording

to the collected data, there are only 12 systems of this kind in Nam Dinh province.

+ Small scale water supply on the basis of groundwater extraction.

In the past, groundwater in Nam Dinh was rarely utilized, only a few extraction wells drilled in Nam Dinh City for the service of industrial hygiene, From 1983, with the help of UNICEF,

with thousands of small boreholes constructed to supply water for domestic use, ean Water for Rural” program has been implemented

Until 2009, the total amount of boreholes constructed with under this program was more than 166000 (see Table 3.1)

UNICEF boreholes are often drilled at the depth of 50-130m in the Quaternary sediment with 40-50mm diameter PVC casing The water is extracted using

handpump or small electric pump with small rate of 04-055 The extraction

depends on the water demand of different areas and households In some communes in Hai Hau and Nghia Hung districts, 100% resident area has the access to clean water from these boreholes.

However, there was no regulation and/or appropriate operation for the extraction of groundwater in the province, Therefore, the boreholes were constructed without ‘manual or guildance (location, depth, etc.) This may lead to contaminant leakages

between aquifers and the risk of depletion of groundwater resources This also

caused difficulties for the modelling process due to the lack of proper pumping data meantioned in chapter 3 It is recommended that more data should be collected to help the improment of groundwater resources management in Nam Dinh Province.

2.2 Geological characteristics of study area

2.2.1 Structural characteristics

‘The Red River (Song Hong) is about 1,200 km long

of Yunnan Provi

originates in the mountains ce in China and enters Vietnam close to the Laos border Its two main tributaries, the Song Lo, also called the Lo River or the Clear River, and the Song Da, also called the Black River contribute to the high water volume of the Red River The river course and the narrow drainage area are regulated by the NW-SE aligned Red River fault system,

‘The pre-cenozoic basement of the NW trending Red River basin began to subside in Neogene time, initiated by the strong uplift of the Proto-Himalayan

mountain chain, High erosion rates resulted in the mobilization of huge amounts of material, which was collected by the tributaries of the major receiving river systems and transported to the Gulf of Tonkin; recent erosion rates reach approximately 130 Million tons of sediments per year (TANABE et al 2003b) During millions of years, deposition and accumulation at the river mouth in combination with ongoing subsidence of the Red River basi finally resulted in the formation of the huge River Delta complex.

‘The axis of the Red River basin is marked by the Red River fault which splits into two branches, the NEer Song Chay fault, and the SWern Song Hong (Red River) fault These two faults bound the Ailao Shan-Red River shear zone The central basin axis contains more than 3 km of Neogene sediments along a narrow 30-50 km wide graben The graben is thought to have subsided totaly about 6 km ‘over the last 50 million years resulting in a maximum long-term subsidence rate of the 0.12 mưa of the central part of the basin,

Figure 25: Quatemary geology and topography of the Red River delta and adjacent areas (Source: Tanabe et al 2006)

‘The tectonic features of the Red River basin are a major driver for the

development of the RRD, Therefore, especially in close vieinity to the adjacent

Mesozoic bedrocks, tectonic structures and features are quite complex This is also

the case for Nam Dinh province which is indicated in the sketch map in Figure 2.6.

Nam Dinh lies above the Ailao Shan-Red River shear zone within the Song Chay and Song Hong fault Previous tectonic studies characterize these major faults as

‘normal fault with dipping 72° NE, Further minor parallel faults displace the

Mesozoic hard rocks One major structural feature in the subsurface of the Nam

Dinh province is the uplifted Vu Ban block (Nguyen Van Cu et al 1996), indicated

by few Proterozoic outcrops in the NW of the province Another important

structural feature is the incision of the paleo Song Hong (Red River) valley, which

is, surrounding the Vu Ban Block and crossing Nam Dinh province to the sea

^XZ hanebaray

Figure 2.6: Geological Sketch map including major structural features and basis

‘boundaries ofthe Holocene, Pleistocene and Neogene sediments (Source: NAWAPI)

‘The cross sections in Figure 2.8 provides a clearer picture of the 2D-Geological

structure (location see Figure 2.7) This provides insight into local and regional

‘hydraulic connections within the hydrogeological units.

Figure 2.7: Sketch map showing location (orange line) of typical hydrogeological cross section of Nam Dinh Province

"`1 SE

[S4] test Hascsne aqui (NỔ 0menesecem aquter

fame] teen sen [id] me Pisce ate

Figure 2.8: Cross section from Vu Ban to Hai Hau (140x vertical exaggeration, ‘modified after Học et al., 2003)

2.2.2 Stratigraphy characteristies

As demonstrated above, the subsurface structure and, thus, the hydrogeology setting of the Red River Delta is somewhat complex Especially in the coastal and ity to the adjacent bedrocks such as it is the ease in Nam Dinh area, active faulting and repetitive transgression and regression events have resulted in a heterogeneous structure of intersecting aquifers and aquicludes Geologic formations in that area with relevance for groundwater supply last from Triassic bedrocks and late Neogene (Pliocene) semi-consolidated sediments up to unconsolidated sedimer of Pleistocene and Holocene time Table 2.1 presents a

stratigraphic overview of Nam Dinh Province.

Table 2.1: Stratigraphy and Hydrostratigraphy of the strata in the Nam Dinh area (Source: NAWAPI)

Suh- | Geologie Facies Bra | System | Series Formation

Series | unit type

Middle |Q"hn | HaNoi [ama

Tower [Qe [Lehi fam

Neogene | Pliovene Nivb | Vinh Bao [am

Proterozoic PRsh | Song Hong

Note: (a) - alluvial; (m) - marine; (b) - swamp bog: (v)-eolian Paleoproterozoic - Red River Complex (PR sh)

‘The ancient metamorphic racks of the Red River Complex mark few elevated hills in the NW of Nam Dinh, which are scattered along a 4 km? area in NW-SE direction Outcrops can be found in Goi, Le Xa and Ngan mountains in the Vu Ban district, as well as Phuong Nhi and An Lao mountains in Y Yen district The mountains mark the top of the uplifted Vu Ban Complex having a structural direction of NNW-SSE and NW-SE Strike slip and reverse faults mark the contact to the adjacent Triassic rocks to the West.

“The Red River Complex mainly consist of:

+ G mmonly found in theiss with biotite, garnet and sillimanite which is Vu Ban Block, Rock texture reaches from small to middle mineral size with spattered large idiomorphic garnet with lengths from 0.5 o 0.8 em.

+ Beside higher plagioclase contents, the Plagiogneis typically found in Goi

and Le Xa mountains contains also biotite, garnet and sillimanite minerals The texture is characterized by small to medium mineral sizes and idiomorphic garnet.

© Phuong Nhi Mountain consist of Quartz schist with feldspar, biotite and garnet, Rock texture is dominated by small pseudo-idomorphie minerals, ‘The Red River complex is subject of heavy folding and faulting in Nam Dinh province

Neogene, Pliocene - Vinh Bao Formation (n; vb)

“The Vinh Bao formation is widely present in the deeper subsurface of the Nam Dinh province, except of areas of the uplifted Vu Ban block in the North-West and West

“Top of Vinh Bao formation was met from 70 m bgl (in NW of Nam Din) down to 151 m bại close to the coast in the SE, maximum observed thickness is >65.0 m.

“The top boundary of the Vinh Bao formation is an expected to be an unconformity

to the covering early Pleistocene sediments of the Le Chi formation and Ha Noi formation

‘Composition of Vinh Bao formation is dominated by fine to medium sandstone with intercalated laminated beds of clay and siltstone, The Vinh Bao formation is believed to be deposited in a deltaic-neritic environment.

Quaternary, Lower Pleistocene - Le Chi Formation (q¡' le)

Le Chi formation was identified at a depth range within 93 to 118 m bgl, The ‘maximum thickness is 18 m and the minimum about 4 m Le Chi formation has an

unconformity to the underlying Vinh Bao formation and to the the upper ~ middle

Pleistocene sediments of the Ha Noi formation,

‘The Le Chi formation mainly consists of coarse grained material such as gravel and medium to coarse sand Sporadically, beds of greyish silt are intercalated The sediments have been deposited in an alluvial to n vine environment.

Quaternary, Upper to Middle Pleistocene - Ha Noi Formation (q;*" hn)

Depth of the top of the formation is increasing from NW (62 m bại) to the SE ‘coastal area (96 m bel) Average thickness is about 24 m with a maximum at 49m, ‘The basis of this formation is represented by unconformity to the Proterozoic and “Triassic basement rocks, Neogene Vinh Bao formation and the Early Pleistocene Le ‘Chi formation, whereas the top generally is an unconformity to the overlying Vinh Phúc formation,

“The Ha Noi formation is separated into an upper and a lower part

‘The upper part is composed of fine sediments such as sandy silt, silt and lay Previous palynological studies indicate that these sediments are deposited in a alluvial to marine environment.

‘+The lower part can be characterized by dominated by medium to coarse grain size sediments with intercalated silt layers, This sub-formation shows fining upward characteristics, with a dominant coarse fraction (coarse sand, gravel) close to the basis and an nereasing fine fraction (fine sand, silt, clay) with

decreasing age This lower part has alluvial origin and reflects the transition toa more marine environment in the upper part.

Quaternary, Upper Pleistocene ~ Vinh Phue formation (q;’ vp)

“The Vinh Phục formation is found from 35 m to 96 m depth, It has an average thickness of about 30 m, with strongly varying maximum of 61 m in the south ‘central part of Nam Dinh and minimum of 12 m close to the adjacent hard rocks in the south west In the West of Nam Dinh area this formations locally overlies directly the Mesozoic and Proterozoic rocks In other areas of Nam Dinh (and the

whole Red River Delta) it typically has a disconformity to the underlying Ha Noi

formation A disconformity to the Holocene Hai Hung formation is generally found at the top of Vinh Phue

‘The Vinh Phuc formation can generally be divided into 3 pasts with differ

* Alluvial Vinh Phục formation: This part can be found locally in Nam Dinh.

It is characterized by a coarse grain fraction (fine to coarse sand, gravel) Dominating minerals are quartz and mica

‘© Alluvial to marine Vinh Phục formation: This part of Vinh Phuc formation contains coarser grain size fraction as fine to medium sand and scattered gravel, representing sedimentation in an alluvial environment

‘© Marine Vinh Phuc formation: This sediment only exists in the south of Nam

Dinh area This part mainly consists of clay and silt of marine origin.

Quaternary, Lower to Middle Holocene - Hai Hung formation (Q:'* hh)

‘The Hai Hung formation widely located in Nam Dinh area and is locally ‘exposed at the surface Top of the Hai Hung formation can be in depths of down to 37 m The average thickness of this formation is about 28 m, but varies strongly with maximum of 45 m and minimum of about 8 m in the vicinity of outcropping hard rocks in the west The Hai Hung formation is generally met sandwiched

between the late Pleistocene sediments of the Vinh Phuc formation at the bottom,

and more recent Holocene sediments on the top,

“The Hai Hung formation is divided into two sub-formations:

® The upper Hai Hung formation including fine grained sediments of marine

origin, including silt and clay, intercalated with fine sandy silt and clay lenses Locally, shell layers occur

+ The lower Hai Hung subformation comprising three facies types

= Alluvial-marine: Mainly grayish silt and clay with intercalated fine sand layers,

- Bog-marine: Dark gray silt and clay with varying fine sand and

remarkable content of plant remnants

- Marine: Brownish grey fine sandy silt and clay, typically contains remnants of gaper shell

Generally the sedimentation environments of the Hai Hung formation reflect the marine transgression of the Early Holocene by the succession of a prevailing estuarine environment up to a more litoral, swamp dominated and finally a gulf environment.

‘Quaternary, Upper Holocene - Thai Binh formation (0;`tb)

“The Thai Bình formation has major impact on the geomorphology of Nam Dinh and represents the source rock for most of the agricultural soils The Thai Bình formation generally overlies the Hai Hung formation with an observed thickness between 37 and 5 m (average 21 m).

“The Thai Binh formation is divided into three sub-formations, They reflect the transition from a marine dominated to a more alluvial envisonment

+ Upper sub-formation comprises marine, alluvial, boggy and eolian facies = Marine: Mainly consist of grey fine sand and silt

= Eolian marine sediment: Beach ridge deposits aligned parallel to recent coast, Due (0 eolian sorting processes the sediments are dominated by fine sand,

- Bog, marine, alluvial sediment: Altemating facies leading to

heterogeneous sediments dominated by brownish grey silty clay and fine sand,

~ Alluvial - marine sediment: These sediments distributed widely in Nghia

Hung, Hai Hau District Their composition included grey fine sand fining-upward to silty clay

= Alluvial-boggy sediment: Sedimentary composition was mainly silt and clay with fine sand.

‘© Middle sub-formation: marine dominated with alluvial influence:

= Alluvial ~ marine: Composition contained brown clay with fine sand and sandy silt layers.

~ Marine sediment: This sediment is widespread close to the surface with ä range of fine sand and ty sand, Typical characteristic are remnants of ‘marine snails (operculum).

‘© Lower subformation: marine dominated with alluvial-boggy influence:

~ Alluvial - marine: These sediments are found in Xuan Thuy and Hai haw

area, Composition is mainly fine sandy silt and clay.

= Boggy - marine: Grayish clay with sand and high content of organic material

Hydrogeological characteristies

23.1 Hydrogeological units

According to Hoc et al 2003, the Cenozoic formations in the RRD can be distinguished into 5 hydrogeological units, namely Upper Holocene aquifer in Thai Binh formation (qhib), Lower Holocene aquifer in Hai Hung formation (qhh), Upper Pleistocene aqui cd in Vinh Phuc formation (qpyp), Lower and Middle

Pleistocene aquifer in Ha Noi formation (qphn) and Neogene aquifer (qp-m2) ''.

i Bi

Upper Holocene aquifer - Th nh formation (qhtb)

‘This aquifer is widely distributed in the district of Hai Hau Nghia Hung, Giao.

‘Thuy Xuan Truong Nam Dinh and Nam Truc Main components of aquifer include

sand, silty sand of Thai Bình formations This aquifer has a hydralic conductivity of K=02-13 miday

Chemical composition and TDS of the water changes very sharply, depending ‘on terrain features and characteristics of water-bearing lens, ‘The TDS has the range ‘of 0.5-23 gi, freshwater lens with TDS < 1g/l are rarely distributed near the rivers, Major recharge sources for this aquifer is rainfall and surface water bodies in Xuan ‘Truong, Giao Thuy, Hai Hau and Nghĩa Hung districts,

In general, this aquifer has a poor potential for groundwater in both terms of

‘quantity and quality, thus Jess significant in water supply However, in some

northern communes in Nam Truc, Truc Ninh and Nam Dinh city, groundwater in small seale for agricultural puposes.

mn (qhhh)

‘This aquifer is not evenly distributed throughout the study area, and is not this aquifer is still used in

Lower Holocene aquifer - Hai Hung form:

exposed on the surface Components of aquifer include sand, silty sand, silly clay of Hai Hung formation, This aquifer has a hydalic conductivity of K = 0.05-04 day.

‘TDS of the water changes very sharply The freshwater lens with TDS < Ig/ are rarely distributed near the Red River Major recharfe sources for this aquifer is rainfall and surface water bodies in Xuan Truong, Giao Thuy, Hai Hau and Nebia Hùng districts

‘This isa very poor aquifer with low water quality, thus less significant in water supply Groundwater in this aquifer is only used in small scale by households living along the Red River

Upper Pleistocene aquitard - Vinh Phuc formation (qpyp)

‘This aquitard is widely distributed in the region with the main lithological ‘composition of clay, silty clay of marine sediment The thickness of this aquitard is ranging from 7m to 34m, This aquitard has a hydralic conductivity of K =

0,005-0.07 míday.

Lower and Middle Pleistocene aquifer - Ha Noi formation (qphn)

This aquifer di ributed throughout the delta area with lithological composition of aquifer include fine sand, coarse sand and gravel of Vinh Phuc, Hanoi and Le Chỉ formation This aquifer has a transmissivity of T = 500-1000 m°/day.

‘TDS in this aquifer ranges from 0.3 to3 gf A large freshwater zone with TDS < {g/l lays beneath the southern districts of Hai Hau, Nghia Hung, Truc Ninh and a part of Nam Truc This aquifer has a very weak hydraulic connection withthe above aquifers (see Figure 2.9)

This aquifer is classified as water-rich with high thickness, wide distribution

area and good water quality This aquifer is currently the main subject of extensive extraction for domestic use in the southem areas of Nam Dinh Provinee It is suggested that there should be appropriate extraction planning and management to utilize and protect this aquifer.

Neogene aquifer (qp-m2)

‘This aquifer is widely distributed throughout the study area Lithological ‘composition includes sandstone, siltstone, claystone, Groundwater exists in the form of fracture and porosity This aquifer has a transmissivity of T = 16-438 m’lday.

‘The chemical composition of water changes vertically Freshwater can be found at the depth of 250 m bại in Nghia Hung district However, water atthe same depth in other districts is mostly saline water.

2.3.2 Groundwater dynamics

Operating by NDWRPI since 1995, the national groundwater-monitoring network represents an important observation source providing groundwater quantity and quality data for more than 18 years The national monitoring network in Nam Dinh comprises 5 stations QI07, Q1O8, Q1O9, QI10 and Q111, comprising 10 monitoring wells screened in the three hydrogeological units gh (5 wells), qp (3 wells) and n (2 wells), Long-term monitoring shows that groundwater level fluctuation are caused by natural factors (climate and hydrological factors) as well

as anthropogenic impacts such as groundwater extraction, lake and canal construction, irrigation and drainage systems.

‘The long-term time series of monthly averaged groundwater level data illustrate some major impacts of these factors According to the behavior of level fluctuation, the sereened aquifers can be allocated to two hydraulic groups (Figure 6) The of data collection in 1995 shallow gh aquifer shows a stable trend since begi

Deficits in the Holocene groundwater budget are balanced by recharge in frame of repetitive phases of irrigation and inundation The seasonal amplitude of up to one ‘Meter indicates a close hydraulic connection with nearby rivers and channels Q1 11 even shows a slightly increasing trend, possibly originated in local subsidence or increasing sea level The second hydraulic group is represented by the time-series of ‘gp and n aquifers indicating hydraulic connected aquifers Obviously, the increasing exploitation of groundwater since the 1990s results in a decreasing trend of groundwater levels in both Pleistocene aquifers of 0.4 m/year (Q108, Q107) up to 0.6 m/year (Q109) The illustrated time series of groundwater level fluctuation is a

typical example for the situation in Nam Dinh and shed some light on groundwater

‘dynamics in this province Shallow groundwater (qh) receives a significant amount of recharge due to hydraulic connection with river, tributaries and irrigation channels It can be concluded that at the transition of the units qh - qp, low permeable aquicludes separate the relatively isolated hydraulic system of unit qh and units qp — n Assuming the majority of abstraction wells are sereened in gp aquifer, the similar behaviour of qp and n indicates a close connection on a regional seale, At the si te with the strongest observed groundwater drawdown (Q109), a relatively high hydraulic head in n is observed indicating a flow recharge of qp from n aquifer.