Assessment of the Upstream Water Quality of a Narrow River using Numerical Modelling

Water quality in Nhue River has been degraded to alarming level, which had some dead parts. Applying MIKE which is a modeling tool for upstream water quality assessment in Nhue River is feasible and reliable. The tool not only simulates results but also helps users assess scenarios and select suitable the scenarios for decision making. In the scenario 1, the water of Nhue River would be polluted more seriously than 2020 and later years because of untreated waste water and fast growth of population and socio -economy. Therefore, the scenario 1 is not suitable for future management planning. In the scenario 2, if 40% of waste stream was treated and the concentration of pollutant in the stream reduced as national regulation, the water quality in Nhue River would continue to decrease slowly but the concentration of pollutants in 2010 would not be slightly different to the figure for 2012. The scenario 2 could be applied i n a short-term plan of improving water quality in Nhue River. In the scenario 3, if the waste stream was treated perfectly before discharging into the river, the water quality would improve significantly and no longer be heavy pollution which means that mo st parameters for water quality would lower than those in 08/2008 regulation. Therefore, the scenario 3 was an optimal scenario for decision makers in management levels. Keywords— water assessment tool; water quality; simulation; numerical modelling; river pollution.


INTRODUCTION
The water in Nhue River from Red River at Lien Mac Drain in Tu Liem District, Hanoi and the end of down stream is confluence between Nhue River and Day River at Phu Ly, Ha Nam. The river runs through Cau Giay, Ha Dong, Thanh Tri, Hoai Duc, Thuong Tin, Thanh Oai, Phu Xuan and Phu Ly. It is 74 km long and 15 to 30 meters wide. The river plays a vital role in ecology, environment and water supply and drainage for Hanoi and near provinces. The Nhue River has been polluted by waste water from agricultural, industrial, domestic and craft village activities and the pollution has impacted negatively seriously to local people's health living near the river. The concentration of Dissolved Oxygen (DO) in some parts of the river was very low so aquatic animals cannot live. In dry season, the river bed with a lot of rubbish appears in many places. [1] There are several researches to examined water quality from the Nhue River as the heavy metal pollution (Kikuchi et al., 2009) [2], Pollution from Capital Urbanization (APEC) , Industrial Science and Technology Working Group, 2010 [3], Industrial Wastewater Management (World Bank. 2010) [4], the chemicalProperties (Nguyen et al., 2013) [5] but has not any research for modelling application at this area. Based on this fact, there was an urgent need for water quality forecasting as a basis for overall environmental management and socio-economic development can be in harmony with river protection. Thanks to the development of science and technology , there are more and more modeling tool used for simulation studies and water quality forecast. An undeniable advantage of using the model is cost savings, high efficiency, high accurate when study in a large areas such as the river basin.The one-dimensional model was used in this study because it is suitable for narrow rivers. In the present study, we applied a modeling to classify and assess Nhue river water quality.

Method for water use and waste water calculation in Nhue River parts
The method for calculating water use and waste water in the research has 2 stages: [6], [7] Stage 1: Collecting the data on pollution sources in river sections in 2015 for the simulation and validation of the MIKE11 model, this data is collected from documents and partly estimated by this method. Stage 2: Forecasting the number of water demand and wastewater of each source by 2020 and 2025 by using this method based on data on population prediction and water demand and wastewater as different purposes. For example, the amount of waste water is 70% of that of water use for domestic purpose.

The method for water quality simulation by the model
The research uses the MIKE 11 to simulate the requirements of three modules: the HD hydraulic module, the AD-transmission module, the Ecolabecological module. Integrating these three modules can simulate water quality. [8], [9] The scope of construction of one-dimensional hydrodynamic model is the all watershed of Nhue River from Lien Mac Drain to Hong Phu Bridge.

Simulating and testing Nhue River water quality by MIKE 11 model
The process of applying Mike 11 to calculate Nhue river water quality changes follows the below chart: [10]

The method of data analysis and calculation
The report will calculate water quality for assessment after having the result of water quality simulation. In particular, the report calculates the water quality index (WQI) as Decision 879 / QD-TCMT on the issuance of handbook for calculating the water quality index. The predict data of nutrient will be compared with Vietnam National Technical Regulation on surface water quality (QCVN 08:2008/MONRE, means QCVN A2 and QCVN B1 in this report) to assess the water quality in the studied watershed area.

Building hydraulic model for the system
-River cross-section River cross section data was mainly provided by the Hydro-Meteorological Center measuring in the river from 2009 to 2014. The data on the sections were added to the model as a cross -sectional database. The sections was marked on left bank, right bank and the deepest point. The average distance between the two sections is 200 m (after being increased thick). The elevation of the terrain in the terrain document and the hydrological document is the same which is taken according to VN2000 standard.

Correcting and testing the hydraulic flow model -Marginal conditions
There is not any monitoring system in Nhue River system therefore the report must use the upper and lower, the middle bound access indirectly. To ensure objectivity, the upper is the flow and the lower bound is the water level. Because of insufficient the data collected from the Center for Hydrometeorology Data -Center for Hydrometeorology, the research simulated the flow and water level in Thuong Cat, Hanoi, Nhat Tan…at marginal conditions based on available water level data.
Input data for correcting and testing hydraulic models was from the National Hydrometeorology Center -Ministry of Natural Resources and Environment. Thus, the data are completely reliable and high accurate.
-The results of correcting and testing the hydraulic model The result of hydrodynamic shows that the water level at comparative points correspond to the actual water level therefore the simulation results can be considered to be successful in building a hydrodynamic model for calculating the dry flow in a basin such as the Nhue River basin.

Setting up the water quality module 3.3.1. Setting the levels for water quality modules
Depending on the requirements of the formular and the measured water quality data, the model level can be set up with the following parameters:

.2. Water quality data analysis
To simplify the process of water quality calculation for the river system, there are three types of WQ water quality were simulated in the model: -The upper and lower: Add water quality data to the HD (inflow or water level).
-Distributed source of each river section: waste discharge points, non-point source in each river section.

Set up parameters for AD
In the AD module, there are some important components need to be set up: Dispersion, Initial Condition and Decay. + Dispersion:

Fig.6: Dispersion value
Decay is also an important parameter demonstrating the decay of pollutants over time. However, for parametors of pollutants which are included in Mike Ecolab, the parametor should not set up in the AD Decay tab. Based on the actual data of the water quality in Dong Nai -Sai Gon River from the Center for Environmental Monitoring in order to set initial water quality conditions for the model.

Set up parameters for Ecolab
The ecosystem module contains many complex parameters affecting biological processes in river water. The important parameters are set up as below figure: The results of water quality simulations by the MIKE 11 model tend to match the trend of actual results from river measurements. Therefore, it is possible to use the simulation results for the assessment of water quality in the Nhue River.

The results of water quality simulation
The simulation of water quality in Nhue River basin aims to increase the quantity and quality of available monitoring points in order to increase the accuracy of water quality assessment in the Nhue river basin.
The quantity and quality of monitoring points in Nhue River as well as the accuracy increased as initial target by surface water quality simulation in the basin. In particular, the number of the actual monitoring points in the river basin was 5 increasing to 133 points after running the Mike 11.  The color for water quality was red (at class 5) and WQI is very low ranging from 9 to 12. It means that Nhue River water at the upstream (from Lien Mac Bridge to Chau Bridge) is heavily polluted so it is necessary to take measures to prevent pollution and improve water quality. The results of WQI illustrate that the quality of river water decreased from Lien Mac Bridge to Cu Da and the closer central city is, the lower the quality of river water is. This is because the number of drainage from residential areas and industrial areas was high and the density of the population and companies were high as well.
The WQIs of the DO, NH4 + -N, Coliform was very low (at 1) because of domestic wastewater accounting for 60% of total wastewater in the whole basin. The wastewater contains organic substances, nutrients, suspended particles and high bacteria which reduced 71% of water quality.
Next reason is waste water from industrial plants, factories and service places in Hanoi. There are a few big factories with waste water treatment systems and the most of factories discharged directly to the Nhue River or through the irrigation system. The Nhue River gets River about 400,000 m 3 of waste water every day from Lo, Clay, Taurus Rivers. The flow also affected by waste water from Van Dien cemetery, Van Dien industrial zone (phosphate plant, battery ...) and municipal landfill.

Forecasting the Nhue river water quality changes run through Hanoi by 2020
The study has retained the central component of the HD model according to the data on pollution in 2020 and replaces the WQ water quality by predicted data on pollution sources in 2020 then incorporated three modules to simulate results of pollution in 2020. There were 3 scenarios (no treating -KB1, treating 40% -KB2 and treating 80% -KB3 on the same chart) at the same time for each parameter, then evaluates the simulation result of 3 parameters respectively (DO, BOD, N-NH4 + ) in 2020, according to the following criteria: -The lower the DO is, the lower the water quality is .
-The higher the BOD is, the lower water quality is .
-The higher the NH4 + -Nis, the lower the water quality is. The results of water quality prediction by MIKE 11 after changing the input data: a/ The prediction for concentration of DO in Nhue River (from Lien Mac Drain to Chiec Bridge) by 2020:

Fig.8: The prediction for concentration of DO by 2020
The concentration of DO in 2020 is predicted to be higher than the figure for observation time due to the fact that there are some measures have been implemented to prevent pollution and improve water quality. In 2020, the figures for To Bridge, Cu Da and Chiec Bridge were lowest. The concentration of DO in Lien Mac Drain is predicted to be a high. In the prediction for the three scenarios, it is clear that the scenario with 80% of the treated wastewater is forecasted to have best results. Therefore, this will be one of the optimal solutions to be applied in the future. However, the government should have a clear plan to treat waste water from 0% to 40% of total then increase the rate to 80% and over 80%. b/ The prediction for concentration of BOD in Nhue River (from Lien Mac Drain to Chiec Bridge) by 2020:  For or scenario 1, it is forecasted that the concentration of NH4 + -N in 2020 will be higher than the figure for current status and much higher than that of QCVN. Moreover, the highest concentration will be in Phuc La, To Bridge, Cu Da and Chiec Bridge. If about 40% of total wastewater is treated, the concentration of NH4 + -N will remain stable by 2020. If 80% of total wastewater is treated, the concentration of NH4 + -N is predicted to be significantly increased by 2020, but it could be higher than the QCVN because there are many ammonium sources from the villages, animal husbandry, cultivation, etc. Overall, the quality of the Nhue River has been deteriorated for the scenario 1. For the scenario 2, 40% of waste streams were treated, Nhue River water quality will maintain the quality at the time of observation while for the scenario 3 with 80% of treated waste streams the quality of Nhue River will improve.

IV.
CONCLUSTION -The quality of the Nhue River has been being degraded at warming level with dead sections. The Nhue River is becoming a sewerage.
-Applying the MIKE to assess the upstream water quality of the Nhue River is entirely feasible and reliable. This toolkit not only provides simulation results, but also helps users evaluate and select suitable scenarios.
-For scenario 1, because of all untreated waste streams and the rapid development of population and the economy, the Nhue River water is predicted to be more and more seriously polluted by 2020 and later therefore it is not suitable for selecting scenario 1 for future management.
-For the scenario 2, 40% of waste stream is treated the quality of Nhue River will be degraded slowly. Therefore, scenario 2 could be used for short-term plan to improve the quality of Nhue River.
-For the scenario 3 with 80% of total waste stream is treated Nhue river quality is predicted to increase remarkably, and there will be not serious pollution. This will be the optimal scenario for decision maker at all level of management.