INTRODUCTION
Introduction
Vietnam has 2360 rivers totaling to more than 10 km and it would appear that this should provide copious supply of water to the nation (http://thewaterproject.org/water-in- crisis-vietnam) However, due to the lack of physical infrastructure and financial capacity there is low utilization of the supply along with an uneven distribution of rain fall resulting in water shortages throughout the country Although Vietnam has improved its water supply situation in the past few decades, many rural parts of the country who are often the poorest communities, have not seen significant improvement It is reported that only 39% of the rural population has access to safe water and sanitation
In Vietnam, both the quantity and quality of surface water are declining despite government efforts to address the issue The expansion of industrial zones and urbanization has resulted in narrowed rivers and altered water flows Additionally, deforestation in upland areas, coupled with climate change, contributes to seasonal flooding and droughts The Ministry of Natural Resources and Environment reports that nearly 80% of diseases in Vietnam stem from polluted water, leading to numerous cases of cholera, typhoid, dysentery, and malaria each year Consequently, the rural population has shifted from using polluted surface water from shallow wells to relying on groundwater sourced from private tube wells In the northern region around Hanoi, there are alarming signs of arsenic contamination in drinking water.
About 7 million people living in this area have a severe risk of arsenic poisoning and since elevated levels of arsenic can cause cancer, neurological and skin problems, this is a serious issue Untreated waste water or treated ineffectively in industrial zones and domestic were released directly into streams, rivers and lakes and popularity of using pesticides, herbicides, chemical fertilizers in agriculture are the causes of surface water polluted The geography and topography of Vietnam also makes the country susceptible to natural hazards such as typhoons, storms, floods and drought This then leads to a multitude of problems such as water pollution and waterborne diseases along with an impact on agricultural lands and livestock Both the environmental pollution in these river basins and natural disasters affects the nation's public health.
The Bui River, originating from the headwaters in Lam Son commune, is vital for the domestic needs and agricultural activities of approximately 5,000 residents Covering an area of 30 km², the headwater catchment experiences significant rainfall, particularly during the rainy season, which can lead to flash floods Although the Lam Son hydrometeorology station has monitored discharge and rainfall data for years, this information has not been extensively utilized to study the river's flow regime Land use changes, particularly due to the construction of the Phoenix golf course in 2004, along with domestic waste and agricultural runoff, have directly impacted the water quality and quantity of the Bui River This research aims to assess the river's water supply potential during dry seasons, flooding risks during rainy seasons, and overall water quality in the headwater catchment of Luong Son district, Hoa Binh province.
Overview of the previous research issues
Runoff generation and water quality have long been key topics in hydrology, a field with a rich history A crucial aspect of catchment hydrology is understanding the discharge hydrograph, which plays a vital role in flood prediction, water resources management, and the transport of chemical and ecological materials Additionally, various processes, including saturated and unsaturated water flow in the soil layer, significantly influence these dynamics.
2008], preferential flow [e.g., Tsuboyama et al., 1994], and Spatial and Temporal Controls on Soil Moisture and Stream flow Generation [e.g., C Jason Williams., 2005] have been examined as dominant processes in controlling discharge.
Various factors influence the hydrology of headwater catchments, with the mobilization of pre-event soil water significantly impacting peak storm flow in steep, forested areas Additionally, both pipe flow and bedrock groundwater are crucial contributors to storm runoff generation.
2009) besides that climate changes also strongly influents to precipitation, evapotranspiration… which are directly effect to runoff generation of headwater catchments (Zhaofei Liu et al., 2009; Z.X Xu et al., 2008)
Headwaters play a crucial role in regulating the flow and quality of downstream water bodies, with any changes in headwater water quality directly impacting downstream ecosystems Variations in land use significantly affect water quality over time and across different regions (Oliver Buck et al., 2004) Key pollutants such as phosphorus (P) and suspended sediment (SS) can degrade surface water quality (R W McDowell et al., 2009), while nonpoint source nitrogen (N) pollution remains a major factor in water quality impairments (Sujay A Kaushal et al., 2011) Enhancing riparian cover near streams has been shown to effectively reduce the influx of phosphorus, suspended sediment, and nitrogen into waterways (Lewis L Osborne et al., 2006).
Research on the Bui River is limited, with only a few studies conducted, such as Hoang Dinh Luu's 2012 evaluation of factors affecting its water quality However, this study did not adequately address the characteristics of the Bui River's flow regime Therefore, a comprehensive investigation into runoff generation and water quality in the Bui River is essential.
OBJECTIVES
This study focus on three main objectives;
(1) Identify Bui River headwater catchment
(2) Evaluating runoff characteristics of Bui River’s headwater catchment
(3) Examining water quality of Bui River.
STUDY SITE AND METHODS
Study site
Figure 1 Location of study site at Lam Son commune, Luong Son district,
Table 1 Climate indicators at Lam Son commune Luong Son district, Hoa Binh province
Month Temperature ( 0 C) Precipitation (mm) Moisture (%)
(Source: Climate software –Institute for forest ecology and environment- Viet nam
Lam Son is a northwest commune located in the Luong Son district of Hoa Binh province, approximately 46 kilometers from Hanoi The area's terrain is characterized by mountainous landscapes and limestone formations, with an absolute elevation of 500 meters and a relative elevation of 130 meters, according to the Institute for Forest Ecology & Environment of VFU.
Geographical coordinates: 20 0 45’ –21 0 01’ in the North
105 0 24’ –105 0 39’ in the EastThe topography of Lam Son consists mainly of limestone alternating with mountains Absolute elevation is 500 m above sea level and relative elevation is 126m The climate of
Lam Son commune experiences a typical tropical monsoon climate, characterized by two main seasons: the rainy season, which lasts from April to October, and the dry season, occurring from November to March of the following year.
Lam Son commune experiences an average annual temperature of 23.1°C, with the highest temperature reaching 28.2°C in July and the lowest dropping to 16°C in January The region receives an average annual precipitation of 1913 mm, predominantly during the summer months of July, August, and September, which account for nearly 95% of the total rainfall December sees the least precipitation, with only 12 mm recorded Annually, there are approximately 146 rainy days, contributing to a significant portion of the rainfall during the rainy season, where 1500 to 1600 mm falls The area's humidity levels are notably high, averaging 84% throughout the year, peaking at 86% in August and dipping to 82% in October.
The wind regime is shaped by general atmospheric circulation and exhibits seasonal variations, primarily characterized by two dominant wind directions From April to October, the Southeast wind prevails during the rainy season, bringing hot air and moisture Conversely, the Northeast wind dominates the dry season from November to April, marking a shift in climatic conditions.
The study area features numerous rivers, streams, ponds, and lakes, supported by a forest covering 1,796.3 hectares, which includes 1,692.2 hectares of planted forest, 22.4 hectares of bamboo forest, and 91.7 hectares of mixed forest, resulting in a forest cover of 56.1% Land use includes 55.1 hectares for domestic purposes, 562.3 hectares for other uses, and 557.9 hectares of vacant land, according to the Forest Inventory and Planning Institute of VFU The region experiences over 70% of its annual rainfall during the rainy season, leading to flooding in the headwater catchment of the Bui River, while dry seasons often result in water shortages for both production and daily living Lam Son commune is home to two main ethnic groups, the Kinh and Muong people, whose economy relies heavily on agriculture, forestry, and some services such as golf and crafts Residents engage in planting rice, maize, fruit trees, and woody trees, as well as raising cattle and poultry.
Methods
3.2.1 Identified the boundary of headwater catchment of Bui River
In 2015, DEM images of Lam Son commune in Luong Son district, Hoa Binh province were utilized alongside Arcmap software to delineate the headwater catchment area of the Bui River, which discharges at the Lam Son hydro meteorological station The process involved systematic steps to accurately define the boundaries of the Bui River's headwater catchment.
Figure 2 Flow chart of identify catchment boundary
DEM images were downloaded from http://gdex.cr.usgs.gov/gdex/:
Step 1: Make a DEM map of Lam Son commune by adding both DEM image and
Lam son map into ArcGis and then using “spatial analyst’s tool/Extraction/Extract tool” by mask
Step 2: Make a contour map of Lam Son commune from Lam Son DEM created at step1 by using “spatial analyst’s tool/surface/contour tool” and then project it using WGS_1984_UTM_Zone 48N
Step 3: Identify flow accumulation of Bui River at headwater catchment by using 3 tools of “hydrology” in “spatial analyst’s tool (Fill tool, Flow direction tool and Flow accumulation tool)
Step 4: From Flow accumulation layer created from step3 I used “Map algebra tool” in “spatial analyst’s tool” to identify streams Then using “stream order and stream to feature tools” to display stream orders.
Step 5:Using “watershed tool” with input is “flow direction” and pour point is the outlet (Lam son hydro meteorological station) to identify catchment area Then combines with Lam Son contour map I had boundary of headwater catchment of Bui River
Figure 3 Illustration graph for discharge measurement
The runoff of the Bui River was assessed using two methods, with the first method involving data from the Lam Son hydro-meteorological station collected between 2004 and 2014 Daily discharge measurements and storm events were calculated using a specific formula.
The stream channel cross section is divided into numerous vertical subsections (7-
The total discharge is calculated by summing the discharge of each subsection, which is determined by measuring the width and depth of the cross-section and using a current meter to assess water velocity.
Water velocity in each subsection was measured using current meter equipment at 0.6 times the water depth To calculate river discharge, the area of the water in the channel's cross-section is multiplied by the average velocity of the water in that section.
The second way, runoff was measured directly in three storm events on three days
20 th August, 2015; 27 th August, 2015 and 30 th August, 2015 by following the same method of Lam Son station
Daily precipitation data at catchment was collected in two period of time The first period from 2004 to 2014 by Lam Son hydrometeorology from 2004- 2014 (lack of data
2005, 2009) and the second period of time is August, 2015 by using Vietnamese rain gages(Fig 4.)
Figure 4 Vietnamese rain gage measurement
To assess the water quality of the Bui River, I analyzed eight key indicators: pH, Total Suspended Solids (TSS), Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Nitrate (NO3-), Phosphate (PO4-), and Coliform levels Water samples were collected before and after storm events using grab sampling methods to monitor changes in water quality.
Water samples were collected in individual bottles, which were then labeled and stored in a black box to shield them from sunlight and heat, ensuring accurate results These samples, excluding the pH indicator, were transported to the VFU laboratory and the laboratory at Hanoi University of Science for analysis of the water quality characteristics at the headwater catchment of the Bui River.
The standard was used for evaluating water quality of Bui River is Vietnam National
Technical Regulation on Surface Water Quality as QCVN 08:2008/BTNMT category B1which is used for agriculture, aquatic life and transport a Total Suspended Solid (TSS)
1 Before sampling, prepare glass fiber filters by first soaking them in distilled water, drying them at 103 o C, and weighing and recording their weights
2 Place the dried, weighed glass fiber filter onto a filtering flask – wrinkled side up Shake the sample bottle first, then pour in the water and turn on the pump (The amount of water you need to filter may change according to water conditions Start with 100 mL Use less volume if the filter gets clogged too quickly and more if the water filters through very fast.) Record the volume of water filtered
3 Dry the filter at 103 to 105 o C, let it cool to room temperature, and weighs it Dry it, cool it, and weigh it again Continue until the fiber reaches a constant weight Record the end weight
4 The increase in weight represents TSS Calculate TSS by using the equation below TSS (mg/L) = ([A-B]*1000)/C
Where A = End weight of the filter
B = Initial weight of the filter
C = Volume of water filtered b pH
Water sample was taken and measured by using pH meter measurement quick test at field c Dissolve oxygen (DO)
Water samples were taken 2 times in each storm events (before storm and after storm) For each time taking water sample, 1 bottle filled of water
In lab analysis, DO tester equipment will be used to test DO indicator of Bui River’s water d Biochemical Oxygen Demand (BOD)
To determine the BOD, we often use sample dilution by adding water into mineral water and saturated oxygen
Oxygen was saturated by blowing air into 1 liter of distilled water and shake until the oxygen saturation then added to the solution of the solution:
1 mL of phosphate buffer pH = 7.2 (dissolved 8.5g KH2PO4; 21.75g K2PO4; 33.4
Na2HPO4.7H2O; 1.7g NH4Cl into 100ml distilled water)
1 mL of magnesium sulphate (dissolved 2.25g MgSO4.7H2O into 100ml distilled water)
1 mL of calcium chloride (dissolved 2.75gCaCl2into 100ml distilled water)
1ml FeCl3(dissolved 0.25g FeCl2.6H2O into 1L distilled water)
Before analysis, water samples must be neutralized to a pH of 7 using either H2SO4 or 1N NaOH For samples with a BOD index below 12 mg/l, dilution is unnecessary.
>= 12mg O2/l diluted with dilution factor 1:1 (1part of distilled water: 1 part of diluted solution)
>= 30 mg/l diluted with dilution factor 1:4
>= 60mg/l diluted with diluted factor 1:9
>= 300mg/l diluted with diluted factor 2:98
Diluted water samples were completely fill into 2 BOD bottles (volume= 300ml) and cap then place the samples in a 20 o C incubator for 5 days
BOD mg/l = (Initial DO - DO5) x Dilution Factor
Dilution Factor = e Chemical Oxygen Demand (COD)
Water samples were collected in plastic bottles Use of plastic containers is permissible if it is known that no organic contaminants are present in the containers
Biologically active samples should be tested as soon as possible Samples containing settle able material should be well mixed, preferably homogenized, to permit removal of representative aliquots
Samples should be preserved with sulfuric acid to a pH < 2 and maintained at 4°C until analysis
The chemical oxygen demand (COD) of aqueous samples can be measured by oxidizing organic matter with dichromate This process quantifies the amount of oxygen that corresponds to the dichromate consumed during the reaction.
The excess dichromate is determined by means of an oxidation-reduction titration with ferrous ammonium sulfate This method is called a “back titration”
1 Pipet 50 mL of standardized K2Cr2O7 into a 500 mL Erlenmeyer flask, place at least six boiling chips into the flask
2 Slowly add with stirring 50 mL of 9 M H2SO4, cool the mixture to room temperature under a stream of tap water
3 Using a hot plate, bring the solution to a gentle boil Cover sample with a small watch glass to minimize the loss of water vapor Digest the sample until completely oxidized The endpoint is since dichromate is still present in significant excess Replace volume lost to evaporation with deionized water Keep the liquid volume about constant
4 Place approximately 200 mL of deionized water in a clean 400mL beaker Slowly add 20 mL of 9M H2SO4 and mix
5 Weigh accurately the appropriate amount of Fe (NH4)2(SO4)2.6H2O to prepare 500 mL of 0.15 M solution Dissolve it in the acid in the beaker, quantitatively transfer to 500 mL volumetric flask and dilute to the mark with deionized water
RESULTS AND DISCUSTION
Parameter characteristics of Bui River’s headwater catchment
Figure 5 Boundary of Bui River’s headwater catchment
Table 2 Parameter characteristics of headwater catchment of Bui River
No Characteristics of catchment Value
4 Drainage density (Dd) 0.91 km/km 2
The Bui River headwater catchment is situated at an average elevation of 206 meters, with the highest point reaching 770 meters and the lowest at 30 meters This medium-sized catchment covers an area of 30.7 km², featuring a perimeter of 27.8 km and a length of 8.7 km The catchment exhibits a maximum slope of 62 degrees, a minimum slope of 0 degrees, and an average slope of 9 degrees With a shape index (Kc) of 1.4 and a drainage density (Dd) of 0.91 km/km², the stream density in the area is notably high The streams predominantly flow in two directions: Northwest-Southeast and North-South, reflecting the typical characteristics of rivers and streams found in Vietnam's northern mountainous regions.
Flow regime characteristics of Bui River at headwater catchment
The rainy season begins from April to October; it takes about 82% (2008) to 97%
(2013) of total annual rainfall Dry season begins from November to March of next year In
From 2004 to 2014, the average annual rainfall at Lam Son was 1764.5 mm, with a peak of 2211.7 mm recorded in 2011 and a minimum of 1308.8 mm in 2010 This rainfall pattern aligns with the monsoon-influenced precipitation variations typical of northern Vietnam.
The flooding season in Lam Son typically occurs from May to October, with total runoff varying between 623mm and 1991mm, accounting for 72% to 92% of the annual runoff Although the onset of flooding can vary, July, August, and September consistently experience the highest runoff, contributing 43% to 66% of the total annual figures During this season, the region supplies between 19.12 million and 61.13 million cubic meters of water downstream Conversely, the dry season lasts from November to April, with runoff ranging from 124mm to 514mm, representing 8% to 28% of the annual total In this period, the headwaters of the Bui River provide between 3.81 million and 15.79 million cubic meters of water downstream, which is crucial for supporting the water needs of local communities and agricultural activities.
Figure 7 Relationship between monthly runoff and monthly rainfall
The relationship between monthly runoff and rainfall is represented by the equation y = 0.574x + 29.621, with a significance level of P