Minimizing the Negative Effects of Irrigation and Hydropower System on Sustainable Development and Environmental Protection in the Huong River Basin45261

Minimizing the Negative Effects of Irrigation and Hydropower System on Sustainable Development and Environmental Protection in the Huong River Basin Nguyen Tien Thanh 1,* , Nguyen Dinh

Minimizing the Negative Effects of Irrigation and Hydropower System on Sustainable Development and Environmental Protection in the Huong River Basin

Nguyen Tien Thanh (1),(*) , Nguyen Dinh (2) , Nguyen Hoang Son (2)

(1) Thuyloi University, Hanoi, Vietnam

(2) Thua Thien Hue Provincial Commanding Committee of Natural Disaster Prevention and Control, Search and Rescue, Thua Thien Hue, Vietnam

*Correspondence: thanhnt@tlu.edu.vn

Abstract: Recently, the effects of irrigation and hydropower system in Vietnam generally and Hue

particularly have been becoming more complex because of the need for considering hydrologic and hydraulic structures in terms of sustainability and environmental protection In practice, irrigation and hydropower operations may yield several undesirable impacts like unsafe conditions for dam operations, flood risks for areas located at the downstream of dams, drought risks or environmental impacts cause natural habitat loss All things may lead to the unsustainable development of social-economic and adversely affect natural resources and environment The goals of this paper, hence, is

to propose the solutions for a minimization of the negative impacts of irrigation and hydropower operations in relationship with natural resources and environment, taking the Huong river basin located in Thua Thien Hue province of Vietnam as an example In this study, the methods of hydrologic and hydraulic modeling, statistical and geographic information system (GIS) is applied

On the basic of attained results, an increase in flood storage capacity of Binh Dien and Huong Dien reservoirs is proposed In addition to this, solutions related to the land cover and inter-reservoir operational process in the Huong river basin are given

Keywords: Huong river basin; reservoirs; environment; hydropower; natural resources

1 Introduction

Hydropower is considered to be one of the largest sources of renewable energy It is interested as cheap, flexible and low polluting renewable energy sources (Kumar et al 2011) Meanwhile, the irrigation reservoirs are considered to be significant role in flood and drought control as well as water supply According to the report of the Intergovernmental Panel on Climate Change (Kumar et al 2011) and SREX (SREX 2015), it is illustrated that hydropower could be vulnerable to extreme weather events (e.g., heavy rainfall) On the other aspect, hydropower could lead to the vulnerability for living-hood in the downstream (e.g., inundations) Therefore, assessment of these constructions mainly relies on water availability assessment as well as flood and drought management and control These play a central role in the objectives of sustainable development

The Vietnamese climate has both tropical and monsoon characteristics due to completely covered by the domain of intertropical zone and monsoon Consequently, climate regime from region to region is unevenly distributed in space and time Combined with the topographic conditions of mountainous and hilly, a high frequency of extreme events is recorded in the whole country Flood events and prolonged droughts can both often record in the same year and region This is a big challenge for the socio-economic

development Located in the coastal area of central Vietnam, Thua Thien Hue province generally and Huong river basin particularly are frequently hit by tropical cyclones, resulting in devastating floods, landslides and other natural disasters Importantly, the issues are compound by the inappropriate discharge from the hydropower and irrigation reservoirs and role of dam operation during heavy rainfall events Under such conditions, the issues of sustainable development and environmental protection have been drawn much attention from scientists and policy-makers, especially in a global warming So the study concentrates on fully interpreting the effects of hydropower and irrigation system and dam

on hydrologic and hydraulic characteristics Then solutions for sustainable development are proposed to minimize negative effects of these systems The HEC-HMS and HEC-RAS models are widely applied due to its advantages for estimating the hydrologic and hydraulic characteristics as pointed out several publications (Sardoii et al 2012; Najim 2013; Wang 2014; Mujumdar 2016).Hence, the study uses a system of HEC-HMS and HEC-RAS

to estimate hydrologic and hydraulic characteristics under different conditions (e.g., dry season or flood season)

2 Methodology

2.1 Study area

The Huong river basin is the largest basin in the northern part of the Central Plain, Vietnam It has an area of about 2830 km2, a length of 104 km and average slope of 2.85% Also, this is a concentrated area of culture, social-economic and politics activities of the Thua Thien Hue province It has three major tributaries, namely the Ta Trach, Huu Trach and Bo The Ta Trach and Huu Trach Rivers unite and form the main flow of Huong River The Bo River merges into Huongriver downstream The Ta Trach River and Huong River mainstream originate from the more than 1700 m height Mountain on the northwest of the Bach Ma mountain range The river then flows in the general direction of southeast to northwest, passing the City of Hue, discharges into the Tam Giang lagoon and finally flows

to the sea at the Thuan An outlet Annual precipitation could be reached up to nearly 4000

mm at places (e.g., A Luoi) (Figure 1) Rainy season starts in starts in September and ends

in December Maximum monthly precipitation is measured at Nam Dong and A Luoi (about

1000 mm) in October The dry season starts in January and ends in August, with June and July being especially hot and dry It is noteworthy that the average annual rainfall in the Huong River basin is always over 2600 mm Recently, lots of irrigation and hydropower reservoirs are developed in the region under the demand of growing energy

2.2 Data

The information on reservoirs that play a significant role in hydrologic and hydraulic regime is collected from management broad of hydropower and irrigation works and Ministry of Industry and Trade of Vietnam (e.g., MOIT 2008a, 2008b) It is noteworthy that only reservoirs that have an effective capacity of more than 100 million m3, over 30MW for hydropower reservoirs and over 10 megawatt (MW) for a combined hydropower and irrigation reservoirs are considered Under these conditions, there are three reservoirs (i.e., Binh Dien, Huong Dien and Ta Trach) in the Huong River basin The information on

technical documents of Thao Long dam, hydropower and irrigation works are included A sample of technical parameters on reservoirs of Ta Trach, Binh Dien and Huong Dien is shown on Figure 2

Figure 1 Location of study area

Figure 2 Parameters of reservoirs

Cross-sections of topographic on the route of river are measured with the information on parameters as presented in Table 1 Besides that, hydro-meteorological data

is collected from the Vietnam Center of Hydro-meteorological data Digital elevation model

of 30 m resolution and Landsat image are also included

Table 1.Number of cross-sections and length of rivers

(km)

Number of cross-sections

lagoon)

6 An Xuan Chanel (Dong Lam- An

Xuan)

Ha Do)

9 5 xa Chanel (Nham Bieu – Bo

river)

sewer)

11 Nhu Y (Dap Da – Dai Giang river) 15.1 29

12 Pho Loi (La Y - Dien Truong

sewer)

2.2 Models

2.2.1 Hydrologic and Hydraulic Modeling

HEC-HMS is a Hydrologic Modeling System that is designed to describe the physical properties of river basins, the meteorology that occurs on them, and the resulting runoff and streamflow that are produced It is physically based and conceptually semi-distributed model and easily operates huge tasks in relation to hydrological studies, including losses, runoff transform, open channel routing, analysis of meteorological data, rainfall-runoff simulation, and parameter estimation (HEC 2008) Moreover, the HEC-HMS uses separate models that compute runoff volume, models of direct runoff, and models of base flow It has nine different loss methods, some of which are designed primarily for simulating events, while others are intended for continuous simulation Advantages and disadvantages of some of these methods are clearly documented (Razmkhah 2016) It also has seven different transformation methods (e.g., the Snyder Unit Hydrograph Yilma and Moges (Yilma and Moges 2008) or Clark Unit Hydrograph Banitt (Banitt 2010) Version 3.5 of HEC-HMS is used in this study

HEC-RAS is a hydraulic model package developed by US ArmyCorps of Engineers

- Hydrologic Engineering Centre (HEC)(HEC 2010a; HEC 2010b) The Hydrologic Engineering Centre’s River Analysis System (HECRAS, version 4.1.0), a one-dimensional, hydraulic-flow model developed by the U.S Army Corps of Engineers (USACE), is to be used for the study The HEC-RAS program is designed specifically for application in flood-plain management and flood-insurance studies to evaluate floodway encroachment and to simulate estimated flood inundation HEC-RAS uses a number of input parameters for hydraulic analysis of the stream channel geometry and water flow These parameters are used to establish a series of cross-sections along the stream In each cross-section, the locations of the stream banks are identified and used to divide into segments of left floodway, main channel, and right floodway At each cross-section, HEC-RAS uses several input parameters to describe shape, elevation, and relative location along the stream (i.e., river station (cross-section) number, lateral and elevation coordinates for each terrain point, left and right bank station locations, reach lengths between the left floodway, stream centerline, and right floodway of adjacent cross-sections, manning roughness coefficients or channel contraction and expansion coefficients) Advantages of HEC-HMS and HEC-RAS are closely connected via the DSS program (HEC 2005) This program is incorporated into most of HEC’s major application programs To validate the performance of the model, Nash-Sutcliffe index (Krause et al 2005) is used











2 2

) (

) (

1 ) (

obstb obs

obs cal

Q Q

Q Q EI

R

Where Qcalis calculated discharge (m3/s), Qobsis measured discharge (m3/s) and

Qobstb is average measured discharge (m3/s)

3 Results

3.1 Pre-processing

3.1.1 Sub-basin and hydrologic-hydraulic network

As the first step, the Huong river basin is divided into 17 sub-basins using the ArcGIS and digital elevation models as shown in Figure 3a On the basic of sub-basins, hydrologic network is produced for HEC-HMS (Figure 3b)

Figure 3.Sub-basin map (a) and hydrologic network (b) for Huong river basin in HEC-HMS

Name Restriction zone Area(km2)

The system of reservoirs and river network is simulated as presented in Figure 4 River network for Huong river basin briefly described as Ta Trach (Duong Hoa), Binh Dien, Huong Dien (Co Bi) reservoirs to Thao Long dam and Dien Hong, Kim Doi, Pho Loi, Nhu

Y, Dai Giang and An Xuan tributaries through the sewers of Ha Do, An Xuan, Quan Cua, Dien Truong, Cau Long and Quan Then they flow into Tam Dang-Cau Hai lagoon and to the sea at the Thuan An and Tu Hien outlets

Figure 4 Diagram of river network and irrigation system in Huong river basin

Tuan

Sinh

Thao Long

Kim Long Loi Nong river

Symbols:

Upper boundary

Lower boundary

Distributarie Junctions Water level control station

Cau Hai Lagoon Tam Giang Lagoon

Quan sewer

Long

Phu Oc

An Xuan

Dien Truong

Ha

Do

Phu Cam

Dap Da

La Y

Thanh

Ha

Bac Vong

Dong Lam Nhu Y river

Tu Hien Outlet Thuan An Outlet

Hoi 5

study domain

Figure 5 Map of hydraulic network in HEC-RAS

Hydraulic network is shown in Figure 5 Grid cells located in the downstream of Huong has a large area Location and area of grid cells are defined by Landsat image in

combination with digital elevation models of 30 m

3.1.2 Calibration and validation of HEC-HMS and HEC-RAS

For the Huong river basin, the flow to reservoirs is calculated on the basic of HEC-HMS at stations (i.e., Thuong Nhat, Nam Dong, Binh Dien, Hue, Kim Long, A Luoi, Ta Luong, Co Bi and Phu Oc) The outputs of HMS are automatically connected to HEC-RAS via the HEC-DSS program Lateral boundary is based on the HEC-HMS output The stations used to validate are Kim Long on the Huong river and Phu Oc on the Bo river Lower boundary is the hourly water level data at the outlets of Thuan An and Tu Hien

For the HEC-HMS model, the performance of the model is clarified under two cases (i.e., daily and hourly discharge) For daily discharge simulations, daily precipitation and discharge data in 1983 and 1986 is used to calibrate the model Daily precipitation and discharge data in 1984 and 1987 is used to validate the model As a result, parameters of HEC-HMS are found out as presented in Table 3

Table 3 Parameters of HEC-HMS model

Sub-basin Station

Parameters

CN Ia tLag (h) Cp Qbq

(m3/s) Rc R x k (h)

Bo river Co Bi 60 2 12 0.45 91.7 0.97 0.1 0.2 6 Huu Trach Binh Dien 60 2 12 0.52 68.2 0.97 0.05 0.2 6

Ta Trach Duong Hoa 60 2 6 0.42 76.5 0.97 0.1 0.2 6

In general, the Nash index for all stations (i.e., Co Bi, Binh Dien and Duong Hoa) reaches over 0.5 Specifically, at Binh Dien station, the Nash index could be reached up to closely 0.7 for both calibration and validation (Figure 6) It is documented that the performance of model well captures the measured data It should be noted, however, these values are considered as acceptable values due to uneven distribution of rainfall stations over the basin The monitoring time is not synchronized More importantly, rainfall regime

is not fully interpreted the discharge regime of the river The reason for this is come from multiple factors affected the discharge regime of the river like elevation slope, patterns of weather conditions and vegetation

Figure 6.Calibration in 1983 (a) and validation in 1984

(b) between calculated and measured discharge for Binh Dien

For hourly discharge simulations, measured data at Co Bi (October 14-16, 1981; October 15-19, 1985), Binh Dien (October 13-15, 1984; October 15-18, 1985) and Duong Hoa (October 10-13, 1986; November 17-23, 1987) is used to calibrate and validate, respectively The simulations closely fit the measured data with the Nash values of 0.9, 0.94 and 0.92 for calibration and 0.78, 0.9 and 0.95 for validation at Co Bi, Binh Dien and Duong Hoa stations, respectively It is emphasized that the peak of flood events could be well captured by the model An example for Duong Hoa station is shown in Figure 7.All outputs of HEC-HMS are used as inputs for HEC-RAS

Figure 7.Calibration in 1986 (a) and validation in 1987

(b) between calculated and measured discharge for Duong Hoa

For the HEC-RAS model, the performance of model simulations is clarified under three cases (i.e., daily water level, hourly water level in water and dry seasons) at stations Kim Long and Phu Oc Daily water level in 1984 and 1999 at Kim Long and Phu Oc is used

to calibrate and validate the model, respectively The results are very good agreement with the Nash indices of calibration (0.56 at Kim Long, 0.57 at Phu Oc) and validation (0.66 at Kim Long and 0.59 at Phu Oc) In case hourly water level in water season, a series of data during the flood event from September 13, 1984 to October 30, 1984 is used to validate It is illustrated an agreement with the Nash indices of 0.63 and 0.77 between the water level simulations and measurement for Kim Long and Phu Oc, respectively In dry season, a series

of data from June 1, 1984 to August 31, 1984 is used to validate the model The Nash value

of 0.62 is estimated for both Kim Long and Phu Oc Figure 8 shows the results of validation for Kim Long in both flood event and dry season

It can be seen from the figure 8 that the peak values are underestimated in comparison with measured data, but acceptable simulations due to the uneven distribution

of rainfall stations Consequently, the climate and hydrological regime are not completely clarified for the basin The parameters of HEC-HMS and HEC-RAS, then, are used to assess the changes in hydrologic and hydraulic features for the downstream of Huong river basin under the impacts of hydropower and irrigation reservoirs