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(2), Nguyen Hoang Son(2) (1) Thuyloi University, Hanoi, Vietnam Thua Thien Hue Provincial Commanding Committee of Natural Disaster Prevention and Control, Search and Rescue, Thua Thien Hue, Vietnam *Correspondence: thanhnt@tlu.edu.vn (2) 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 socialeconomic 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 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) 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 Figure Location of study area Figure Parameters of reservoirs Cross-sections of topographic on the route of river are measured with the information on parameters as presented in Table 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 Nr River Length (km) Number of crosssections Huu Trach (Binh Dien – Tuan) Ta Trach (Duong Hoa – Tuan) Huong (Tuan – Tam Giang lagoon) Bo (Huong Dien – Sinh) Bo (Bac Vong – Dong Lam) An Xuan Chanel (Dong Lam- An Xuan) Dien Hong Chanel (Dong LamHa Do) Kim Doi (Thanh Ha – Quan Cua) xa Chanel (Nham Bieu – Bo river) Dai Giang (Phu Cam – Quan sewer) 7.7 14.5 34.3 24 59 31.3 4.2 9.64 37 8 10.2 6.0 14.3 17 27.1 39 10 11 12 13 Nhu Y (Dap Da – Dai Giang river) Pho Loi (La Y - Dien Truong sewer) Other rivers surround Hue city 15.1 5.9 29 6.1 16 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 floodplain 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, NashSutcliffe index (Krause et al 2005) is used  (Q R ( EI )    (Q cal obs  Qobs )  Qobstb ) Where Qcal is calculated discharge (m3/s), Qobs is measured discharge (m3/s) and Qobstb is average measured discharge (m3/s) 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 Table Detail information of sub-basin Name Restriction zone Area(km2) LV1 LV2 LV3 Restricted basin by Bau Son Restricted basin by O Ho river Restricted basin by Rao Trang river 454.5 351.4 300.5 LV4 LV5 LV6 LV7 Restricted basin by Rao Nho river Restricted basin by Huu Trach river Restricted basin by Tra Ve rivulet Restricted basin by Day rivulet 409.4 360.9 157.9 58.3 LV8 LV9 LV10 LV11 Restricted basin by Rao Binh Dien river Restricted basin by Ma Ray river Restricted basin by Ta Man rivulet Restricted basin by Dau rivulet 109.5 231.8 238.8 247.2 LV12 LV13 LV14 Restricted basin by Chon rivulet Restricted basin by Huong river Restricted basin by Huong (downstream) river 89.2 130.0 293.0 Name Restriction zone Area(km2) LV15 LV16 LV17 Restricted basin by Phuong rivulet Restricted basin by Nong river Restricted basin by Truoi river 161.4 115.2 147.3 The system of reservoirs and river network is simulated as presented in Figure 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 Huong Dien Huong river Tuan Bo river Huu Trạch Binh Dien Ta Trạch Ta Trach Phu Oc Hoi Kim Long Loi Nong river Huong river Phu Cam Nhu Y river Bac Vong Thao Long Cau Hai Lagoon An Xuan O Lau river An Xuan Chanel Quan Cua Diern Hong Chanel Dong Lam Kim Doi river Huong river Sinh Quan Long Dien sewer Bridge Truong Ha Do Tam Giang Lagoon Tu Hien Outlet Symbols: Thanh Ha La Y Pho Loi river Dại Giang river Nong river Truoi river Dap Da Thuan An Outlet Upper boundary Lower boundary Junctions Distributarie Water level control station study domain Figure Diagram of river network and irrigation system in Huong river basin Figure Map of hydraulic network in HEC-RAS Hydraulic network is shown in Figure 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 HECHMS 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 HEC-HMS are automatically connected to HECRAS 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 Table Parameters of HEC-HMS model Parameters Sub-basin Station CN Ia tLag (h) Cp Qbq (m3/s) Rc R x k (h) Bo river Co Bi 60 12 0.45 91.7 0.97 0.1 0.2 Huu Trach Binh Dien 60 12 0.52 68.2 0.97 0.05 0.2 Ta Trach Duong Hoa 60 0.42 76.5 0.97 0.1 0.2 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 a) b) 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 shows the results of validation for Kim Long in both flood event and dry season It can be seen from the figure 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 Figure 8.Validation of HEC-RAS for Kim Long in dry season (June 1, 1984 – August 31, 1984) (a) and in flood event (October 1984) (b) 3.2 Main impacts of hydropower and irrigation reservoirs on hydrologic and hydraulic regimes The features of hydrologic and hydraulic for the downstream of Huong river basin are considered at water level control stations (Kim Long and PhuOc) 3.2.1 Changed flows in flood season For the flood season, typical flood events in 1999 and 1983 are selected to interpret the changes in hydrologic and hydraulic characteristics The cases are mentioned including (1) TH1: Non-reservoirs and dam, (2) TH2-PA1: Reservoirs and dam are operated under each reservoir operation produce, (3) TH2-PA2: Reservoirs and dam are operated in collaboration with the flood controlling under water levels of flood alarms at the downstream, (4) TH2-PA3: Reservoirs and dam are operated with the increasing of flood storage capacity for Huong Dien and Binh Dien Table Changes in flood characteristics before and after constructions at Kim Long in corresponding to the historical flood in 1999 Flood characteristics at Kim Long TH1 TH2-PA1 TH2-PA2 TH2- PA3 Maximum water level Hmax (m) 6.09 5.81 5.13 5.1 Flood intensity to the average 0.20 0.15 0.09 0.1 0.54 0.52 0.24 0.35 101 97 96 93 water level (m/hour) Flood intensity to the maximum water level (m/hour) Time for water level ≥3m (hour) Table shows changes in flood characteristics before and after constructions at Kim Long in corresponding to the historical flood in 1999 It is illustrated that with the constructions of reservoirs and dam, the characteristics of floods are significantly changed in comparison with non-reservoirs and dam With the reservoirs and dam, the flood peak is pulled down to 5.81 m (TH2-PA1), 5.13 m (TH2-PA2) and 5.1 m (TH2-PA3) from 6.09 m (TH1) More importantly, the time of flood occurrence that water level is higher than m is significantly decreased by 16 to 25 hours The flood intensity to the maximum water level is reduced by 0.02 to 0.3 (m/hour) Similarly, Table shows changes in flood characteristics before and after constructions at Kim Long in corresponding to the historical flood in 1983 It is observed that with the constructions of reservoirs and dam, the characteristics of floods are relatively changed in comparison with non-reservoirs and dam With the reservoirs and dam, the flood peak is pulled down to 4.7 m (TH2-PA1), 3.81 m (TH2-PA2) and 3.56 m (TH2-PA3) from 5.0 m (TH1) More importantly, the time of flood occurrence that water level is higher than m is significantly reduced by to hours The flood intensity to the maximum water level is reduced by 0.02 to 0.2 (m/hour) Table Changes in flood characteristics before and after constructions at Kim Long in corresponding to the historical flood in 1983 Flood characteristics at Kim Long TH1 TH2-PAI TH2-PAII TH2- PAIII Maximum water level Hmax (m) 5.00 4.70 3.81 3.56 Flood intensity to the average water 0.09 0.07 0.06 0.05 0.35 0.33 0.15 0.14 57 48 49 48 level (m/hour) Flood intensity to the maximum water level (m/hour) Time for water level ≥3m (hour) 3.2.2 Changed flows in dry season The dry season is defined from January to August The results in changed flows at the Kim Long and Phu Oc are presented in Figure Figure Changed water level in Phu Oc (a) and Kim Long (b) in dry season for inter-annual flows with and without dams and reservoirs As shown in Figure 9, it is illustrated the role of reservoirs and dam are reasonable The flowsarestable with the effects of minimized tidal Water level is increased by 0.81 m opening the conditions of potential water exploitation for agriculture and water supply for other areas 3.3 Proposal on minimizing the negative effects of irrigation and hydropower system on sustainable development The results show a significant effect of irrigation and hydropower system on the changes in hydrologic and hydraulic features over the Huong river basin Advantages of these systems are salinity preventing, water level control in dry season and reduced-flood peaks The potential disadvantages are mentioned (e.g., potential inundations in the downstream of Huong river when unreasonable reservoir operation or reduced sediments at the Thuan An outlet) Importantly, flood with the frequency of less than 10%, Ta Trach plays a central role in reducing the inundations in the downstream Meanwhile, the role of Binh Dien and Huong Dien reservoirs are negligible under the issued reservoir operation processes of Vietnam In dry season, all hydropower and irrigation system could be seen from the stabilizing and increasing of flows Thao Long dam prevents the negative effects of tidal on the downstream of Huong river basin With the obtained results, proposal on minimizing the negative effects of irrigation and hydropower system is concentrated on the construction solutions Presently, Ta Trach reservoir has the largest flood storage capacity of 556.2 million m3 in comparison with a total storage capacity of 646.0 million m3 Meanwhile, flood storage capacity of Binh Dien is 70 million m3 out of total storage capacity of 423.68 m3 (accounting for 16.5%) Notably, there is not a flood storage capacity for Huong Dien reservoir Table gives a proposed values for minimizing the negative effects of reservoir system with Vpl is flood storage capacity and Vho is total storage capacity Table Proposed Flood storage capacity for reservoirs Reservoir Present Vpl (106 m3) Proposal % Vho Vpl (106 m3) % Vho Ta Trach 556.2 86.1 556.2 556.2 Binh Dien 70 16.5 150 35.4 Huong Dien 0 200 24.4 Total 626.2 33 906.2 48 The study calculates the efficiency of this solutionfor specific cases as follows: (i) Binh Dien reservoir with the flood storage capacity of 150 million m3 and water level before floods of +65.03 m; (ii) Huong Dien reservoir with the flood storage capacity of 200 million m3 and water level before floods of +51.63 m; (iii) Ta Trach reservoir with the flood storage capacity of 556.2 million m3 and water level before floods of +25 m; and (iv) Thao Long dam is completely opened For historical flood events in 1983 and 1999, the results in water level of flood peak are presented in Table Table Water level of flood peak in the downstream of Huong river basin under the increasing of flood storage capacity Flood event in 1983 TH1: TH2: Changes in Vpl Vpl2 water level (m) Kim Long 4.70 3.56 -1.14 Phu Oc 4.43 4.30 -0.13 Flood event in 1999 TH1: VPL TH2: Changes in Vpl2 water level (m) 5.81 5.10 -0.71 4.60 4.47 -0.13 Obviously, it can be seen from the Table that Binh Dien and Huong Dien reservoirs with the increasing of flood storage capacity lead to the water level reducing at the downstream of Huong river basin in both 1983 and 1999 Specially, the water level of flood peak at Kim Long on the main Huong river falls down to 3.56 m from 4.7 m in 1983 and 5.1 m from 5.81 m in 1999 Besides that, the study also proposes to enhance the vegetation cover in the upstream of reservoirs system With the forest zone, it prevents the erosion, landslide or jumping sand and reduces the sediment of reservoirs Conclusions The study presents the effects of reservoirs and dam system on the hydrologic and hydraulic characteristics in the downstream of Huong river basin Importantly, the main impacts of hydropower and irrigation reservoirs on hydrologic and hydraulic regimes are fully interpreted in both flood and dry season The water level in dry season is increased for exploitation activities in a variety of different fields like agriculture Meanwhile, flood flows are partly controlled with the reservoir and dam system More importantly, the solutions of non-construction and construction are proposed to minimize the negative effects of these systems on flows and water level in the downstream The proposal is to increase the flood storage capacity for Binh Dien and Huong Dien from 70 to 150 million m3 and from to 200 million m3, respectively References Banitt A (2010) Simulating a century of hydrographs e Mark Twain reservoir In Proceedings of the 2nd Joint Federal Interagency Conference Las Vegas NV USA Halwatura, D and Najim, M.M.M(2013) Application of the HEC-HMS model for runoff simulation in a tropical catchment Environmental modelling & software, 46, 155-162 Hydrologic Engineering Center (HEC) (2005) HEC-DSS Vue HEC data storage system visual utility engine: User’s manual Krause, P., Boyle, D.P., Bäse, F (2005) Comparison of different efficiency criteria for hydrological model 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