Impact of the Hoa Binh Dam (Vietnam) on Water and Sediment

Open Access at Son Tay near Discussions 1 Sciences − t yr Earth System Earth 6 Hydrology and and Hydrology 10 × 4 334 333 in the river mouths. Water regulation has led to 1 , and V. C. La − 1 t yr 6 10 × , D. T. Tran 2,3 and was commissioned in December 1988. Although being important 3 m 9 10 , S. Ouillon 1 × This discussion paper is/has beenSciences under (HESS). review Please for refer the to journal the Hydrology corresponding and final Earth paper System in HESS if available. Institute of Marine Environment and Resources, VAST, 246 Danang Street, IRD, Université de Toulouse, UPS (OMP), UMR 5566 LEGOS, 14University av. of Edouard Science Belin, and Technology of Hanoi (USTH), 18 HoangVietnam Quoc Institute Viet, of Meteorology, Hydrology and Environment, 62 Nguyen Chi Thanh, ocean (Milliman andcent Syvitski, human activities 1992; on Farnsworth large rivers and have severely Milliman, altered sediment 2003). discharge, mainly However, re- turbidity maximum zone in theenhanced Cam-Bach sediment Dang deposition estuary in aresedimentation the probably rates the Haiphong are cause harbor. coincident of Along withserved the the the since lower coast, the sediment impoundment the delivery of reduced the that Hoa has Binh been Dam. ob- 1 Introduction Asia and Oceania contribute 70 % of the global sediment supply from land to the dry season. Suspended sedimentsouthern discharge estuaries proportionally and increased decreased inpumping, through northern which the and causes main a andcharge, net is central sediment high Ba flux in Lat from4.5 the mouth. m the northern Tidal in coast delta, spring to as tide; the a diurnal estuary consequence tide). of at The the low shifts high dis- in tidal the range dynamic (up and to characteristics of the Red River basin, in50 yr the dataset delta of and waterand discharge in the and the suspended distribution coastal sediment of zone.calculated concentration water (1960–2010) Its using and impact the sediment was MIKEAlthough analysed across 11 water numerical from the discharge model nine atpended before mouths the sediment and of flux delta after dropped, the inlet the onHanoi, delta decreased average dam and from was by settlement. 119 from only to 85 8.8 43 decreased %, to water the 35 discharge yearly in sus- the wet season and increased water discharge in the The Hoa Binh Dam, locatedof on 9.45 a tributary offor the flood Red prevention, River electricity in production, Vietnam,Binh and has Dam irrigation a has capacity in also northern highly influenced Vietnam, the the suspended Hoa sediment distribution in the lower Abstract Impact of the Hoa Binhwater Dam and (Vietnam) sediment on budgets inRiver the basin Red and delta D. V. Vu Hydrol. Earth Syst. Sci. Discuss.,www.hydrol-earth-syst-sci-discuss.net/11/333/2014/ 11, 333–370, 2014 doi:10.5194/hessd-11-333-2014 © Author(s) 2014. CC Attribution 3.0 License. 1 Haiphong City, Vietnam 2 31400 Toulouse, France 3 Cau Giay, Hanoi, Vietnam 4 Hanoi, Vietnam Received: 25 November 2013 – Accepted: 23Correspondence December to: 2013 S. – Ouillon Published: ([email protected]) 10 January 2014 Published by Copernicus Publications on behalf of the European Geosciences Union. 5 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 − tyr 6 10 (To, 2000 × 1 − s 3 in 2000), while , as compared (Milliman et al., 1 1 − erent time scales 2 − ff yr yr 2 km 3 (Tanabe et al., 2003, − 3 2 10 ects deltas (Ouillon, 1998; × ects sediment fluxes in the ff ff ciency of the Hoa Binh reser- (Luu et al., 2010). ffi 2 − over a 40 yr period in the Yellow 1 − tyr 6 in 2000. Although Luu et al. (2010) esti- 10 in 1949 to 300 000 m 1 × 1 − 336 335 − yr (Achite and Ouillon, 2007). At 160 yr 3 3 1 − yr 2 − over a 20 yr period in the Yangtze River (Changjiang) 1 − at Son Tay (Milliman et al., 1995; Pruszak et al., 2002), cor- tyr 1 during the period 1997–2004 following the HBD impoundment 6 − 1 − 10 tyr 6 × tyr 6 10 in 1949 to 300 000 m 10 × 1 − × yr 3 This paper aims at completing the previous studies both in the Red River basin and The Red River water and sediment discharges are distributed amongst a complex The Red River (Song Hong) drains a basin area of 160 The Red River delta (RRD), located in the western coast of the Gulf of Tonkin, is the dynamics. three main tributaries were averagedand over after a HBD long-term impoundment (for series 20The yr of before, variability measurements 1960–1979, of before and 22 water yr(seasonal, and after, 1989–2010). interannual) sediment and discharge the areconcentration examined impact have at of been di HBD continuously is measuredexist upstream, assessed. in but Discharge the no and Red systematic River sediment tions. records delta, This where paper only water alsodistribution level provides is amongst available a the at first nine thesimulations estimate distributaries, hydrological and sta- for of assesses before the the and water consequences after and for HBD, the sediment from estuaries discharge numerical and coastline morpho- mated the water discharge distributiondelta in the after northern, HBD central commissioning, and theRed southern water River part and across of its suspended the nine sediment mouths distribution has of yet the to bein its documented. delta before and after the HBD impoundment. Water and sediment fluxes from the distributaries, is silting upconsequences (Lefebvre rendering et urgent al., thechanges 2012). need in This for the an silting river analysis basin. upcrease of In has of the suspended huge suspended coastal sediment sediment economic zone, flux downstreamBa Van Maren of Lat (2004) the area. showed HBD After that a thelow the dam water de- impoundment, increased alongshore (from sedimentin 200 transport 000 deeper m rate waters in (10–30 shal- 500 m) 000 m in the Ba Lat coastal area, it decreased from a peak of voir was estimateddelivery to to be the delta 88 %, by half suggesting (Dang et that al., thenetwork 2010). HBD of reduces connected annual distributariessediment discharge, sediment with Haiphong harbor, nine located river in the mouths. Cam Despite estuary, one the of the decrease northern in (Le et al., 2007). The mean annual sediment trapping e to around 40 quoted by Le etRiver al., and 2007). the The Da RedRed River (or River has Black) system, two River. until mainet The the tributaries, al., building latter the of 2010). was Lo the Before theto (or Hoa HBD main be Clear) Binh impoundment, 100–160 sediment Dam the provider (HBD)responding Red to in River to the the sediment a 1980’s flux (Dang to specific was a sediment estimated global delivery averagethe of of Red 700 River 120 to tkm wasMeade 1100 ranked (1983). tkm Recent as studies the have shown 9th that river the sediment in flux terms drastically decreased of sediment flux by Milliman and 2005; Hori et al.,above sea 2004; level. Its Luu population et wasan estimated al., average as population 2010). 16.6 density million The of in RRD 1160 2006, inhabitants corresponding lies km to entirely below1995). three Its average meters discharge over 1902–1990 at Son Tay was 3740 m River (Huanghe) (Wang et al.,Asia 2006, have also 2008). been Large impacted by riversirrigation, other and human dredging, their activities and such deltas deforestation as in (Tran groundwater et Southeast pumping, al., 2004; Saito etfourth al., largest 2007). delta in SoutheastIrrawaddy, Asia and in Chao terms Phraya of8000–9000 delta deltas. yr plain The ago. surface, RRD after It the initiated thenSon Mekong, prograded in Tay, and with the expanded a vicinity to triangular of reach morphology Hanoi its with about current an area apex of near 14 300 km et al. (2003) estimatedin reservoirs. that This around reduction of 53 %Syvitski sediment flux of and dramatically sediment Saito, a flux 2007).approximately is For 150 now example, potentially sediment(Yang trapped et discharge al., decreased 2006) from and 480 from 1200 to to 150 as a consequence of artificial impoundments (Syvitski et al., 2005). Vörösmarty 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 − (Le 1 − for the 2 km ) and a min- 3 1 − s 10 3 × with monthly peak 1 − ). Approximately 90 % 1 − s (52 % in Vietnam) for the 3 2 km 3 10 × with monthly peak of 360 mm month 1 − 338 337 , respectively, and the average sediment con- 1 − , before the HBD impoundment, with a maximum tyr 1 6 − 10 × 1 gL ∼ 120 (64 % in Vietnam) for the Lo. The Da River also originates in ∼ 2 during the highest flood ever recorded in 1971. The discharge at in 2006, and 1725 mmyr 1 km and − 1 3 − 1 − 10 yr × 3 downstream of the apex of the delta (Gourou, 1936, quoted by van Maren, 5 − 10 × After the confluence of the Da, Thao, and Lo rivers, the Red River gradient falls to Mathers and Zalasiewicz,20 1999). % of The the Duong-Thai total water Binh discharge River (General carries Department of approximately Land Administration, 1996). The total water and sedimentwere discharge 120 km of the Songcentration Hong in at the Son river Tayestimated gauging was at station 12 gL the Hanoi station reached aimum maximum in during July–August the (about dry 23 000of season m the (January–May; annual typically sediment 700 m discharge flowed during the wet season (Mathers et al., 1996; homogeneously distributed over theet whole al., basin area, 2007). from Episodically,from typhoons 880 July to hit to 1150 the mmyr November.across northern the They coastline coastline move (Matthers of in and Vietnam Zalasiewicz, a 1999). principally northwestern2.3 direction and strike Hydrological regimes obliquely and sediment transport mer monsoon from the southson and (from a May winter to monsoonthe October) from total alternates yearly the rainfall. with northeast. In a the Thein period dry wet 1997–2004, the season sea- the mean and whole annual accounts rainfallage basin was for 1590 value (Le 85–95 mm % estimated et of who to al., give be 2007). the 1667 It mm extremeof is values between 450 slightly mm obtained 1996 month during higher and 10in on yr: 2006 1996. the 1345 by The mmyr delta, mean Luu annual with et potential an al. evapotranspiration aver- from (2010), 1997 to 2004 was rather the Day mouth. The Ba Lat mouth is the2.2 main mouth of Climate the and Red rainfall River. The Red River basin is subject to a sub-tropical climate that is characterized by a sum- mouth, the Tra Ly mouth, the Ba Lat mouth, the Ninh Co (or Lach Giang) mouth, and form the Nam Trieu mouth), the Lach Tray mouth, the Van Uc mouth, the Thai Binh Hanoi: the Red River to theIn southwest the and the southwest, Thai the BinhNinh Red River Co to River River the system and northeast the includes (Fig.a Day 1). the main River. On distributary. Tra At the Ly Pha left River, Laiand bank the in of sediment Red the the from delta, River, Red the the the River, Duong-Thaithe the Cau Binh Luc Duong River system Nam River (288 receives River is km water (200 long), kmparts long) the of and the Thuong Red supplies River River water delta. (157 andto Finally, km the sediment southwest, long) Red-Thai to the Binh and the river Cam-Bach northeastern system Dang has, from mouth northeast (the Bach Dang combines with the Cam to city (Nguyen and Nguyen,the 2001). The Gulf Red of River Tonkin (BacSea). flows Bo, 1200 km in before Vietnamese) it in empties the into East Sea5.9 of Vietnam (South China 2007) and the river diverges into two major distributaries a few kilometers upstream of River in China,because and of flows its reddish-brown into colorrichness Vietnam water, of due where to sediments it its inthe huge is sediment iron Da named delivery dioxide. River and the The and toThao Hong Red Lo the River River River or (of (Fig. receives Thao whichDa, 1). two River and 21 Their major % 34.6 drainage tributaries: is basinsthe in Yunnan are province, Vietnam), 57.2 the 51.3 elevation ofRiver is its located source in being China at at 2000 an m. elevation The of source 1100 m, of and the joins Lo the main branch at Viet Tri 2.1 Geomorphology The Red River sourceof is the located Yunnan province with in a China mean (Nguyen elevation and of Nguyen, 2000 m 2001). in It the is mountains named the Yuan 2 Regional settings 5 5 20 25 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | . 1 − ) at 1 − s . Its an- 3 of water, 1 − 3 m . Its average ) at the Cau 1 9 1 − − s 10 at the Thac Buoi 3 × (or 42.3 m 1 − 1 s − ). Since its impound- 3 yr of water corresponding 3 3 (or 40 m m 1 9 − (Nguyen, 1984; Nguyen et al., (Nguyen, 1984; Nguyen et al., yr 10 or 51.2 m 1 1 3 × − − 1 − tyr tyr yr 6 6 3 (Nguyen, 1984; Nguyen et al., 2003). 10 10 1 − × × tyr 340 339 6 http://www.icold-cigb.org/ 10 and will produce 2400 MW of electricity. Construc- × 2 km 3 10 × 40 % of the Vietnamese electricity production (Le et al., 2007). ∼ Salinity intrusion occurs for up to 40 km landwards from the Cam River mouth within The construction of HBD on the Da River began on 6 November 1979 and ended of the delta, around Ba Lat mouth, is a mixed tide and wave-dominated coast. 2.6 Fluvial, tidal and wave influencesFluvial-, along tide- the and delta coastline wave-dominatedment processes of appear the RRD, to but their be(Mathers relative important and influence Zalasiewicz, is in 1999; subject van the to Maren, aof develop- 2004, remarkable the 2007). spatial RRD The variability lies northern sheltered coastal frommouths section strong are wave mostly action tunnel-shaped by as the aforces. island consequence In of of the Hainan, the and prevalence southern of theas part river river a and of consequence tidal the of the delta, dominant the wave river forces (Pruszak mouths et are al., mainly 2005). convex The in central part shape from the Ba Lattends mouth. much However, farther the upstream. At tidal Phuwater influence Ly levels (120 on km vary water from by the level 1 coast)et and m on al., discharge during the 2010). Day ex- the River, dry daily season and 0.6 m during the wet season (Luu The tide in the Gulfoccurring of each Tonkin day, is and predominantly an ato amplitude diurnal south gradually in decreasing type, spring with from tides 4 one14 m (Fang ebb-flood days et to cycle al., cycle, 2 m 1999; the from Nguyen0.5 north et tide m al., during amplitude 2014). neap Within at tides. the Ba spring-neap Lat variesthe from delta, 2.5 38 m km from during the spring Lach Tray mouth, tides 28 to km from the Thai Binh mouth and 20 km HBD, is under construction. Thea Son catchment La area dam of 43.76 has ation capacity began of in 9.26 December 2005,commissioned it in was 2014. impounded in May 2010 and2.5 it is expected to Tide be and tidal influence in the estuaries irrigation supply in northern Vietnam. A second dam, the Son La, located upstream of 2010) and the Ba LatMaren, river 2004, mouth 2007). shifted 10 km southwards to its currenton position 30 (van December 1988.to HBD 17.8 % has of a the capacity1920 MW, annual of delivering discharge 9.45 ofIn the Da 2012, River it andCommission was has on ranked an Large 53rd electric Dams, power inment, HBD plant ICOLD, the has of played world an in important role terms in flood of prevention, electric electricity production, capacity and (International The last four major floodsous within high the return floods period inrole, of the representing 100 Lo, yr 53–57 % were Da of caused and totalever by Thao discharge simultane- recorded, (Le rivers. et the The al., water Da 2007). During River level the usually in biggest played flood Hanoi the reached main 13.3 m in August 1971 (Luu et al., nual sediment discharge is on2003). average The 0.12 annual dischargethe of Chu the Luc station, Nam withIts River annual an is sediment average discharge 1.3 km averaged suspended2003). 0.2 These sediment rivers concentration experience a of81 flood % 330 season of mgL from their June total toThai October annual Binh which water River brings system. input 70– and 85–92 % of2.4 their total sediment Dams input to the The annual discharge of thestation, Cau with an River average is suspended 1.6annual km sediment concentration sediment of discharge 250 mgL isThe 0.22 annual discharge ofSon station, the with Thuong an average River suspended is sediment concentration 1.2 km of 122 mgL 5 5 25 20 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) 1 (3) (4) − (in mg j , i (in tyr , d i , y C , is the number M i p , and erence model for one i ff and year j and year ) and suspended sediment con- j ratio) was calculated as: Q Q 342 341 amongst the 9 distributaries of the Red River k ) and suspended sediment discharge 1 − yr amongst the 9 distributaries of the Red River, the ratio of 3 k 0.0864 (2) × (in m ) is the average water discharge at day j i , , 1 i , y − d s Q C . 3 86400 (1) i , flow, sediment transport, and water quality in rivers, channels, estu- l × × ratio can be calculated for a given year or from the average of yearly l ff j k j M , , Q k i i , 1 , (in m 1 M M 9 Q d = 9 d P = l j P l , Q i Q were calculated following norm TCN26-2002, as: , ratio) for a given distributary 1 = 1 d = i p = p = k j Q k X j X M = = ) is the suspended sediment concentration at day i i , ratio ratio and , 1 ratio For a given distributary y y − its water discharge to the Gulf of Tonkin (denoted Q In the same way,noted the ratio of suspendedwas sediment calculated delivery as: to the Gulf of Tonkin (de- M Q M where L of days per year The annual water for year time before (1960–1979) and2010). after The (1989–2010) data HBD was impoundmentat collected (MONRE, by the 1960– the hydrographic National stationsYen Hydro-Meteorological Bai of Service (Thao the (NHMS) River), Red Hoaand River Binh Thuong system (Da Cat (Fig. River), (Duong Son 1):TCN26-2002 River). Tay Vu Calculations (Red of Quang were River), the (Lo Ha carriedcoastal River), Noi erosion out Vietnamese along (Red according the Hydrometeorology River) to RRD the from General Tran norm et Department. al.3.2 (2001, Data 2002, 2008) on are Calculation also of used. water and sediment discharge in upstream rivers 3.1 Data Data used in thiscentration paper (SSC) are over daily the water 50 discharge yr ( period from 1960–2010. This time period covers the 3 Data and methods dimensional unsteady flow computationquasi-two and dimensional can flow be simulationto on applied perform floodplains. to detailed The modelling looped of modelovertopping, networks rivers, culverts, has including and gate been special openings treatment designed and of weirs. MIKE11 floodplains, is road capable of using kinematic, In order to estimate waterbefore and and sediment after discharge HBD from impoundment, estuaries athe into data-driven the MIKE11 modeling coastal model approach zone (Vu was et setupof using al., surface 2011). runo MIKE11 isaries, a and modeling floodplains package (DHI, for 2004). the MIKE11 simulation is an implicit finite di Q values over a given period. 3.3 Calculation of water and sediment3.3.1 discharge in estuaries The MIKE11 model 5 5 15 20 10 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (5) and cients Q erence ffi ff s. During during the 3 / 1 1 − − relation, wind usion of SSC is ff Q/h ), Q cient of 0.03 m , a negative value indicating e, 1970) calculated for each ff ffi −∞ ), discharge ( h until the simulated and observed wa- erences between the predicted and ob- n ff 344 343 and SSC data before (1960–1979) and after (Nash and Sutcli Q E cient ffi 2 ) 2 ) Q Q varies from 1.0 (perfect fit) to erent combinations of ff E relation can only be applied to the downstream boundary. In order calc mean used during the calibration process were within the range of 0.020– ciency coe − − ffi n Q Q/h Q e e s as recommended by Chow (1959). To avoid model instability, appropriate obs ff ( obs 3 ( / . The erent locations in the river reach. During calibration, the simulated and ob- 1 P ff ff P − − 1 usive or fully dynamic, vertically integrated mass and momentum equations. The The values of For calibration and validation purpose, the model was run with actual data, for real In order to setup the model, the Red River system was designed under a network = ) at di ff n E The model was calibrated by( changing the values of Manning’sserved roughness water coe discharge atwere Ha compared Noi, for di Thuongter Cat, levels matched Nam closely. Dinh, OptimizationNash–Sutcli Cua of Cam the gauging model’s parameterssimulation sites and was given based by: on the Ba Lat, Ninh Co andcalculated Day by River mouths. the While model SSC duringflood at period. ebb these periods, estuarine we boundaries was chose to fix it3.3.3 at 50 mgL Calibration and validation as boundary conditions in the Bach Dang, Cam, Lach Tray, Van Uc, Thai Binh, Tra Ly, Buoi (Cau River), CauSSC were Son used (Thuong as River) inputs and at Chu these cross-sections. (Luc Hourly Nam water River). levels Daily were imposed situations. For studying theas impact defined of from HBD, the(1989–2010) the average HBD impoundment. model of The was daily hourlythe run boundary river conditions for mouths in two came water from elevation typicaland at measurements 2006, years performed respectively. at the gauging stations in 1979 3.3.2 Boundary conditions Upper boundaries were fixed across sections at Son Tay on the Red River and at Thac which includes the main rivers (Fig.collected 2) from by data the such NHMS. as river Inbefore section the every and true calculation bed simulation elevation the began. model ran for 32 days for the spin up the hydrodynamic regime (characterized by theary Froude number). can The be discharge applied bound- to eitheralso the be upstream applied or to downstream the boundary sidepict conditions, tributary runo and flow can (lateral inflow). Theto lateral simulate inflow suspended is used sediment toused transport, de- in a which module erosion ofule and advection/di requires deposition outputs are of from expressed thelevel, as hydrodynamics cross-sectional source/sink module, area namely terms. and water This discharge, hydraulic water radius mod- and calibrated specific parameters. solution of continuity and momentumscheme. equations This is based scheme on is anspecified. structured implicit Boundary finite so di types as includefield, to dambreak, water be and level independent resistance ( ofeither factors. the the The wave water upstream description level or boundary downstream must boundary be conditions applied in to the model, depending on di tational time step and gridwater size level were and assigned discharge as conditions 30tially, s the were and model provided 1000 was m, to run respectively.the Initial using avoid initial a a uniform runs, dry roughness the bed coe model situation. over-estimated Ini- water level at some stations. Local values that the mean valuethan of the model the (Krause observed et time al., 2005). series would have0.035 been m a better predictor computational time step and grid size were selected. In the model setup, the compu- in which the sumserved of values the is absolute normalized squared byunder di the investigation. variance of the observed values during the period 5 5 25 20 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2 − 11.8 %, (Fig. 4), + 1 (Van Rijn, − 2 . The rate of − yr 2 3 − m 9 10 × ects the discharge of Red 0.902) as are the Red and ff for our simulations. The criti- = 2 2 − r s (upstream and in the riverbeds) 3 , that of the Duong River increased / 1 1 − − for the periods 1960–1979 and 1989– yr 1 . The average annual water discharge − 3 was used in our simulations. The critical 1 − yr m 1 ) was tested in the range 0.005–0.25 Nm . In other words, the portion of discharge 3 9 − 1 yr c,d 346 345 − 3 m τ 10 9 yr m × 3 9 ) was tested in the range 0.1–1.0 Nm 10 m 10 . erent locations along the river to obtain the best fit × c,e 9 1 ff τ × − 10 s was then calculated to quantify the model performance 2 cient from 0.035 m × 109.4 %, Station 5; Table 1). This shows (1) that the HBD − ffi + E were high. Rainy season (June to October) water discharge Q and 105.8 kg m 47.8 %, Station 3 – see location in Fig. 1), Red River ( 1 3 + cient − − ffi 0.899). As a result, the HBD not only a yr s (downstream and in the main channel). cient of variation, denoted CV and defined as the ratio of standard 3 3 = / ffi m 1 2 were chosen at di − r 9 n 10 × ciency coe ffi values for water discharge in Ha Noi, Thuong Cat, Nam Dinh and Cua Cam were Regulation of HBD has led to changes in the water distribution of the Da, Red and The trends of the inter-annual variability in yearly water discharge are not straight- The measured yearly water discharge exhibited small increases per tributary af- Seasonal variations of Lo and Thao Rivers supply about 50 % of the total water discharge of the Red River, The e Stokes’ law was used to determine the free settling velocity of the suspended par- forward. The coe deviation to the average, is a suitable indicator of variability. While the inter-annual Duong Rivers. Discharge increased significantly duringment dry on periods the post Da HBD River impound- ( Station 4) and Duong River ( has a marked impactRiver on responds water to regulationsection variations at above in the the connection the seasonal with Red the scale Thai-Binh River, and River. particularly (2) in that Duong the dry season in the poundment, to 31.5 %. represents 71–79 % of annual total(December discharge to with April; only 9.4–18 Table 1). % during Therainfall the remaining (January, dry February, 5–10 and % season occurs March). during the period of lowest charge of the Da andDuong Rivers Red ( Rivers is highlyRiver but correlated also ( that of the Duong River. ter HBD commissioning (TableRiver 1, and 1.9 Fig. % 4): for thecreased 7.3 Da % by River. 8.8 for Conversely, % while from the theby 116.1 yearly Lo to Red 13.9 River, %, 105.8 River 4.6 discharge from % de- diverted 29.2 for by the to the Thao 33.3 Duong River increased from 24.5 % of the Red River before HBD im- with an averagewas value 116.1 of 110.0 2010, respectively (Table 1, Fig. 4). the remaining 50 % being provided by the Da River (Table 1). The monthly water dis- from year to year, over the range 80.5 (in 2010)–160.7 (in 1971) good agreement between measurementssediment and transport simulations (i.e. the during wet the season; main Fig. 3). period for 4 Results 4.1 Water discharge in the mainThe tributaries Red RiverRivers discharge (Fig. results 1). from Between its 1960 and three 2010, major the tributaries, Red Da, River discharge Thao at and Son Lo Tay varied with daily averagegust measured 2006 upstream water (HaE discharge Noi, and Thuong Cat) sediment0.75, and 0.72, concentration 0.71 downstream and (Nam in 0.69,tion respectively. Dinh, The Au- at Cua values for the Cam). suspended same sediment stations concentra- were 0.67, 0.66, 0.65 and 0.65, respectively, thus providing ticles in thisflocculation, study. a Assuming settling a velocityerosion of low shear 0.2 stress concentration mms of without sediment ( hindered2005); after settling calibration, we and selected thecal no value deposition of shear 0.2 stress Nm of sediment ( (Van Rijn, 2005); after calibration,erosion we chose was set to apply at a 10 value of 0.15 Nm between measurements and simulations. Thea decreasing resulting roughness calibration coe was obtaineddown with to 0.02 m of Manning’s 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 1 1 − − and over tyr 1 1 6 − − 17.3 %; . The an- 10 − 1 × − (Table 1). (Table 2). At 1 1 − after ( − 1 tyr − 6 tyr before the HBD was 10 6 1 × − 10 × tyr 91.1 %). This is equivalent 6 − 10 to 0.74 erences after impoundment and 61.3 %; see Table 1, Fig. 4), cor- 1 × ff − − after ( tyr 1 6 − 10 tyr for the period 1989–2010) and Thao River × 6 ect on sediment discharge and SSC in the 1 ff − 348 347 10 ; Table 1, Fig. 4), whereas sediment discharge over the period 1989–2010 (Table 2). Interest- 1 × tyr 1 − 6 − t in 1971 before HBD impoundment and between t in 1990 for the period after 1989. tyr 6 6 10 6 × 10 10 10 × × × . As a consequence, annual total suspended sediment 1 after the impoundment ( − (about half of the total supply to the Red River delta) before 1 − 1 − tyr to 51.7 6 1 tyr − 6 10 tyr 10 before the HBD was also reduced to 21.6 × 6 1 × − to 105.7 mgL 10 1 t in 1963 and 201.0 t in 2010 and 133.6 tyr × − 6 6 6 in the Da River was multiplied by 1.75 after HBD impoundment. 10 10 10 Q × × × Despite contrasted changes in the inter-annual variability of river discharge, the main The seasonal variability of SSC is high. Total suspended sediment discharge is high- The HBD impoundment had a strong e Before HBD impoudment, SSC of the Thao River was, on average, 1728 mgL aries in the north of the RRD slightly increased after impoundment: from 15.5 % (before in the Red Riverin by suspended 31 load % (Table56.0 and 2). in At the the Duong10.4 Son River Tay by station, 13 sediment % flux due ranged to4.3 between a large Influences decrease on the distributaries discharge The water distribution acrosswas the estimated 9 from numerical river simulations mouths (Table 3). before Water and discharge after ratio of HDB the impoundment estu- iment discharge onequivalent the and ranged inter-annual between 32.2 scale. %before (Red While River HBD at their impoundment, Son Tay) they respective andvaried 36.3 had CVs % from much (Thao were River) 38.8 higher % almost di inlute the change Duong of River the to standard 77.4 deviation % decreased in significantly the in Lo the River. Da Moreover, River the by abso- 88 %, est in July andment August discharge and for lowest fivefrom in months 87 February of % and the to rainy AprilSSC 96 % was season (Table the (Table 2). (from highest 1). in Suspended June While theto sedi- to Da the 70 River October) % CV (111.9 made after, %) amongst before it up 80 HBD the %, remained impoundment respectively monthly quite and (Table 2). dropped averaged unchanged The values changea in in of decrease the the of Da Lo 6–7 River % and sediment of regime Thao the also rivers, involved seasonal around variability 90 ofrivers SSC and of in the the Red Red River and system Duong show Rivers. an enhancement of the variability of relative sed- see Table 1, Fig. 4),the and the period average of SSC 1960–1979 decreased toingly, by the 738 25.4 total mgL %, suspended from sediment delivery 989 mgLseason in after the Duong HBD River impoundment, slightly from increased 0.46 in dry Thuong Cat on the Duong28.9 River, the annual total suspended sediment which averaged river was 65.0 HBD impoundment, itto dropped only to 7.8 5.8 %Fig. of 4). the At cumulated contributions1193 the mgL from Hoa Da, Binh Loof gauging and the station, Thao Red the Rivers Riverreduced annual (Table to at 1, average 46.1 Son SSC Tayresponding decreased which to from averaged a 119.3 decrease in the average SSC from 1027 to 397 mgL nual total suspended sediment fluxfor increased the both period in 1960–1979 the to Lo 12.7 (from River 43.4 (from 9.2 and SSC decreased in the Da and Red Rivers. Da, Red and Duong Rivers. While annual total suspended sediment discharge of Da 4.2 Suspended sediment discharge The total suspendedwater sediment discharge discharged as well from asand the Da on Rivers. Red the suspended River sediment system concentration of depends the on Lo,was Thao always higher than therespectively; mean Table 2). SSC The of SSC the of Da the Red and River Lo (at Rivers Son (1193 Tay) was and 1027 mgL 306 mgL a CV ofDuong 15.2–15.3 River, % it shown amongst higher variations yearlyfrom upstream: 23.2 values) from 10.4 to and to 14.8 17.8 % decreasedCV % for of for by the the Da only Lo River, River 2.8 % and from for 14.2 the to 52.7 % for the Thao River. The variability did not change for the Red River at Son Tay after HBD impoundment (with 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 − yr 3 22 %, m ∼ 9 for 1960– 10 t for the dry 1 − 6 × , see Table 3) 6 and s ratio were ob- 1 3 10 − ∼ M × yr 3 25, m ∼ 9 t to 1.7 10 6 × 10 during the dry season, while × 3 for the period 1960–1979 and of m 1 9 − s 10 3 × t for the rainy season (Table 4). As a result, . Their percentage for the Van Uc-Thai Binh 1 6 350 349 − during the rainy season (Table 3). This lower 10 3 or 3678 m tyr × 1 m 6 − 9 for 1989–2010 (Table 1, Fig. 4). These values are . The changes in suspended sediment distribution yr 10 1 1 10 3 − − × s × m 3 tyr 9 t to 30.5 6 6 10 10 × 10 × for 1989–2006, and those of other reports or papers (To, 2000; × 1 − or 3353 m s 1 3 − yr 3 m 9 10 ratio decreased in the central part of the delta. Although the suspended sedi- × M No estimates of water distribution amongst the 9 estuaries have been published for The value of 31.5 % of water diverted by the Duong River and calculated over 22 yr Although the HBD does not influence yearly water discharge, its regulation has mod- The decrease of suspended concentration of the Red River caused a strong de- The decrease of total water discharge from all the distributaries of 10.2 respectively. Our value for Ba Lat is also consistent with that of van Maren and Hoekstra the period before HBDof impoundment, the however, water Pruszak discharge etdate percentage al. is for (2005) 6 not gave estuaries, given estimates butsuspended which sediment they are flux probably reported of refer 116 in tosystem Table pre-1989, (37 3. %) as The is they very consider closesystem to a (38.6 our % global estimate for yearly before Cam, 1979well Bach for (10 the % Dang, whole by Lach Duong-Thai Pruszak Tray Binh Ba and et Lat, Thai al., Ninh Binh), 2005, Co and vs. and for 8.4 Day % the estuaries in Tra are Ly our the as calculation). same The and estimates represent for the during the wetter period 1996–2000 to 35 % during theified drier the 2001–2006 range period. ofseason seasonal in variation. the Water Da discharge Riverand increased by (at by 109 Hoa % 47.7 Binh % in station), the in by Duong the 11.8 River dry % (at in Thuong the Cat). Red River (at Son Tay) 105.8 consistent with the previous1988, and estimates 3426 of m DangNguyen et et al., al. 2003; Le (2010): etare 3557 al., based m 2005). on This data is provided to by be the expected same as administration. all ofis the in determinations very goodet al. agreement (2010) with who the calculated former an estimate average over diversion of 11 yr 30 %, (1996–2006) with by variations Luu from 25 % The values ofdataset water of and discharge and sedimentcan sediment discharge concentration be at compared calculated five with keywater in the discharge stations this previously of of 116.1 published the study values. Red from We River found a an 50 average yr annual 5 Discussion and conclusion 1989 from 84.8 tomirror 35.1 the changes ofserved discharge in distribution the i.e. northernCam slight Rivers) part increases and of in of the thethe southern delta part (from (from 15.5 22.1ment to to discharge 22.8 in 17.1 % % absolute in value inin the decreased Day the Cam-Bach in River), most Bach Dang whereas distributaries, estuary Dang itble slightly 4). in and increased dry season due to an increase in river discharge (Ta- crease in suspendedcharge sediment in the concentration distributaries. asdry Total suspended and well sediment rainy season delivery as after decreasedseason, suspended HBD both and impoundment from in sediment from 77.3 the 2.6 dis- the total average annual suspended sediment discharge decreased by 58.6 % after between 1960–1979 and 1989–2010calculated (from by 130.5 the to model 120.3 should is be due noted to that awere water decrease use not of for considered the irrigation, Red inestuaries drainage, River the urban increased discharge model. and slightly (Table industrial 1). Between fromit purposes It the decreased 17.8 two from to periods, 98.8 20.8 variability water to of 85.2 discharge water discharge of is the mainly a consequence of water regulation by the HBD. Tray River, from 13.6 toBinh 14.5 % River. for It the also Van23 Uc increased %. River, Conversely, in and this from the value decreased 6.0 Dayfrom in to 24.9 River, the 6.4 to at % central 22.5 the delta, in % especially the (Table south 3). at Thai of Ba the Lat mouth delta, from 22.1 to HBD) to 16.5 % for the Cam and Bach Dang estuaries, from 3.5 to 3.7 % for the Lach 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 1 to − 1 , re- ects − 1 ff tyr − 6 10 at the Son × 1 − t settle per year, ) calculated over 1 6 − 10 tyr ected by the impound- × 6 t as quoted by van den ff 6 ). This latter range is con- 10 to 397.4 mgL 1 10 × − 1 − × tyr 6 10 × ) given by Pruszak et al. (2005). The value 1 352 351 ) is also very close to the value calculated by − . This decrease of 91 % is consistent with an 1 1 − tyr − for 2003–2010; see Fig. 4). 6 tyr 1 tyr ) for the period 1979–2008. The interannual vari- − 6 10 1 6 − × 10 tyr 10 6 × tyr × c and the outgoing tidal waters out (Tran et al., 2002). 6 10 ffi 10 × × ciency trapping of 88 % in the HBD (Dang et al., 2010). ffi in the Da River and represented about half of the total supply to 1 − ) than during 1989–2010 (10–134 1 tyr at Hoa Binh (Da River) and from 1027 mgL − 6 1 − tyr 10 6 × 10 × The increase of the suspended sediment discharge ratio in the northern and south- By limiting flow during floods, the HBD regulation decreased sediment transport ca- The highest value at Thuong Cat station as compared to the Son Tay station may The distribution of sediment discharge from the Red River to the RRD coast changed After the HBD impoundment, average daily SSC decreased from 1193 mgL The average sediment flux in Hanoi before HBD (119 Concerning the suspended sediment discharge, it should be noted that there were The present calculations show that water distribution was a pacity of the rivers therebyof enhancing obstructing deposition in the the river, boat with tra the knock-on e However, it is consistentestimated with by Häglund the and value Svensson of (2002). 70 % ofern sediment estuaries delivered and to itsaccretion the decrease zones sea at along as the thecal, RRD Ba biogeochemical and coasts, Lat ecological they responses mouth in also(e.g. influenced the altered Rochelle-Newall estuaries, not et delta, the and al., only geological, coastal 2011; areas erosion morphologi- Bui and et al., 2012; Navarro et al., 2012). Da rivers is lostrepresenting in 31 % the delta. ofdelivered Between to the the Hanoi ocean. sediment This and percentage dischargethe is the similar at absolute to sea, that Son quantity 11 of 1960–1979 is Tay,guess (29 the %), since divided however, the remaining by model part does 3. not being This take into estimate account neither should flocculation be nor stratification. considered as a first estimated sediment e be explained byindustrial, either agricultural new origins or sediment fromby inputs dredging activities riverbed between such and as the bank observedGuennec, erosion in two 1996; Hanoi), induced stations van or by Rijn, (from the 2005). local urban, river load capacityboth (Ouillon spatially and and Le quantitatively, decreasing fromconsider 85 the to 35 period million t 1989–2010, (about 58.6 50 %). % If of we the sediment brought by the Lo, Thao and 105.7 mgL Tay Station on the Redwas River. 65 The annual totalRed suspended River, sediment decreased discharge, which to 5.8 sediment discharge (24.5 1960–1979 is the sameagreement with as other previous that estimates that calculatedwith ranged a between by 100 very and Dang close 160 etcalculated estimate for al. (116 1989–2010 (2010). (46 ItDang is et also al. inability (2010) good of (49 sediment201 transport in Hanoisistent was with the higher range overBergh estimate et the of al. period between (2007b), 30 1960–1979 although and we (56– 120 found a smaller lower limit due to the recent lower (Yuanjiang river), as illustrated by1960s, the 1970s, average 1980s SSC andspectively, at 1990s were the where observed Manhao values station (He ofsuch during 1870, et as 2490, the shifts al., 3120, in 2007). land 3630 mgL Other use and impacts deforestation in may also China contribute and to these in changes. Vietnam ment of the HBD.Lach While Tray, the Van water Uccreased ratio and at of Thai the the Binh) Ba northernestuaries Lat increased estuaries increased mouth from by (Bach from 17.0 38.6 % Dang, 24.9season in to to Cam, after the 22.5 the 41.1 dry %. % HBD season The impoundment, after and total due decreased 1989, water to by discharge water it 13.7 regulation. % from de- large in the the increases rainy in sedimentThese discharge were and partly concentration caused in by the human Thao activities and in Lo the rivers. Chinese part of the Red River a dry year (2006)average and post-1989 a yr. wet The year percentagesare (1996) of very post-1989, Luu close while to et ours our al.our were estimates; (2007) estimates with calculated for than those for for the for an dry the three years wet main being years. outlets in better agreement with (2004): 21 %. Other calculations were performed by Luu et al. (2007, see Table 3), for 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (van den 1 − , turbulence Q , Do et al., 2007). 1 , respectively. This − 3 and the rapid accre- m 1 3 − 10 × culties for navigation, similar ffi 354 353 t of sediments annually dredged from the port in 6 10 ) and tectonic subsidence (2 mmyr × 1 − . Shoreline changes obtained from maps suggest that the Hai Hau 1 − It is not possible to test this hypothesis using hydro-sedimentary studies due to the the Hai Hau district was subsiding with a maximum rate of up to 5 mmyr tion in front ofto the Haiphong river bay. Conversely, mouths sedimenterosion. caused deficits Coastal in widespread erosion the di causes adjacentThe loss areas coastal of led zones land, to where andmouth shoreline rapid the to erosion expansion the prevails of are Hai(Do saline located et Hau intrusions. al., from district 2012), south such (see ofcan as location reach the north 15 in of Ba myr the Fig. Lat Ninherosion 1), Co started mouth. and Shoreline around in regression therate in the beginning Hai during nearby Hau of the the the late mouths 1960s. 20th According century to with geodesic a measurements decrease from in 1963 erosion to 1985, ing sea level riseTypical (1–2 mmyr mechanisms ofbars delta in propagation front involvement of the of the forming the mouths and deltariver (Do connecting outward mouths et sand into were al., the expanding 2012), at Gulf thus a of inducing rate Tonkin. Recently, a of the progressive about shorelines develop- 15–100 myr at these probably due to the generalmodified decrease dynamics of of river the capacityregulation turbidity of of maximum, sediment water both transport flow ofPhong or by which to in HBD. are the The 1922, directly dredged relatedis 1983, volume to compared 1992 of the to was sediment aboutorder 922.6, in the to the 1256 4–5 guarantee port the and port ofpublished). 1700 During activities Hai the today last (Vietnam geological Administrationmouths period, of also the Hai had Van very Phong, Uc, rapid un- Thai accretion Binh, zones Tra with Ly and sediment accumulation Ba rates Lat exceed- the recent increase of sediment deposition in the middlelack and lower of estuary. data availablein prior the to volume theenhanced of HBD silting sediment impoundment. up dredged However, of from the the the recent estuarine harbour changes Cam-Bach of Dang Hai estuary Phong. illustrate This increase the in silting is and the volume of fluid mud. In the Cam-Bach estuary, it is probably a major feature of east of the delta (Cam-Bachand Dang, Lach south Tray and delta Van Uc estuarieset estuaries) al., because than 2002). in the the Other tidal central forcingsuspended factors amplitude particulate also is matter modify is tidal therecentration, pumping. strongly much Flocculation especially dependent higher of in on (Uncles estuarine the lowhas suspended energetic been sediment identified episodes as con- (Verney the etson most important al., in factor the 2009) controlling aggregation Bach andand in Dang turbulence SSC the estuary wet variability sea- caused (Lefebvre by etbidity dam maximum al., regulation zone 2012). and and The to changed changes dam its of retention characteristics, displaced such the as tur- its seasonal trajectory that marine water flows intocycle the shows estuary a during strong floodriod. and velocity The high asymmetry, observed enough with slight so aimpoundment increases that of short of the the tidal river but HBD discharge likely highlypumping enhanced during energetic (Allen the the et tidal flood al., dry asymmetry pe- 1980; and season Dyer, the after 1986). associated Tidal the tidal pumping is probably higher in the north- water periods than lowmum slack (Allen waters, et thus al., favoringconsolidates deposition 1980; slightly near Uncles during neap the et tides turbidity al.,sediment (Dyer, maxi- 1985; 1986). deposition Lefebvre Dyer, induced et 1986; al. by Dronkers, (2012)up tidal showed 1986). pumping to that Fluid in three mud the timesdry Cam-Bach higher Dang during season, estuary the the can dry netCam-Bach be season Dang sediment relative estuary, flux to bringing the at backfloods wet (Lefebvre into the et season. the al., river During 2012). estuary Tidal mouth the particles pumping is occurs brought when by positive river previous discharge from is low the enough sea to the Dang, Ninh Co andto Day improve Rivers navigability. In resulting the inby the middle the dynamics and need of lower for thedients; estuaries, turbidity increased deposition Sottolochio maximum dredging zone is et in (e.g. mainly al., tidalwith order driven pumping shorter 2001). and/or and Tidal density more pumping gra- energetic is flood periods caused than by ebb the periods, and asymmetry longer of high slack tide, Enhanced deposition occurred in the middle estuaries, in particular the Cam-Bach 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | cient ffi , respec- 1 − , respectively. for 1991–1995 1 − 1 − ), and “strong” erosion (more than 1 − 5 m, 5–10 m, 10–15 m decreased by 63, 56, 356 355 < Pb in sediment cores show that the sediment 210 ected water discharge and the suspended sediment in- ff ), “mean” (2.5 to 5 myr 1 − in the period 1965–1991 and up to 15.0 myr 1 − erent scenarios, before and after HBD period (Vu et al., 2011). This ff shore (at about 20 m depth, HP6), the average sedimentation rate for the ff ) by Tran et al. (2002). In the period 1965–1990, the length of eroded coastline 1 − River dams have been built in Viet Nam for many decades for energy supply, such In the coastal area, recent measurements of sedimentation rate at the outer Tra In order to assess impacts of HBD on the distribution of suspended sediment along To distinguish between various erosion levels, the intensity of erosion was noted as 5 m, 5–10, 10–15, 15–20, 20–25, 30–35 m decreased by 62, 66, 65, 54, 42, 36 %, River delta are presentlyof silting the up HBD and whichriver this has discharge led is in to partly the a northern duedeposition the delta to in decrease during the the in Cam-Bach the water sediment Dang dryment transport estuary. flow season. Moreover, discharge and the regulation All of decrease of an Red of which increase River suspended likelyshoreline. induced of sedi- enhance Coastal a erosion decrease intensifies of when sedimentationbalance sedimentation rate sea and along accumulation level the no rise delta longer account and tectonic when subsidence considering and daman this regulation. integrated factor management Finally, needs this plan to that work be extends underlines taken from into the the need river for basin to the coastal zone during the first decades.sediment However, fluxes. recent In studies summary, from havesiderable its documented impoundment, role their Hoa in Binh impacts Dam floodHowever, on it has control, also played a significantly irrigation con- a andput from electricity the production Red in River basin North to Vietnam. the delta and coastal areas. The estuaries of the Red season, averaged SSC on waterand depths 39 %, respectively. These resultsa show higher that impact the on reduction shallow ofof water sediment the areas, delivery central up has delta, to where 15by m tidal morphologic in asymmetry changes the (van are north Maren driven and et by up al., wave to 2004). action 10 m moreas in than the front Day DamRiver), in and 1937 the (on HBD the in Day 1989. River), Sediment the trapping Thac in Ba the Dam reservoirs in was 1970 not (on considered the Chay polymeric substances, EPS) in thein aggregation the which Cam-Bach have Dang beenHaiphong estuary shown to (Mari Bay be et area e al., and< 2012). during The the simulations shown wetrespectively, that, season, after in HDB the the impoundment. averaged In SSC front on of the water Ba depths Lat mouth and during the wet model did not take into account the influence of polysaccharide polymers (extra-cellular was setup with di rate in this areaMouth (station is HP4 decreasing in (Bui Bui1966–1975, et et 1975–1988, al., and al., 2012), 1988–2011, 2012). was theFurther 1.8, average At 1.24 sedimentation o and 10 rate m 1.01 for cmyr depth theperiods periods in 1964–1976, front 1976–1984, of 1984–2011tively. was the This 0.67, River tendency 1.0 is andriver coincident 0.56 to cmyr with the sea the after reduction HBD of impoundment. sediment inputthe from Red the River Red delta, an integrated model (hydrodynamics-waves-sediment transport) for this period. The Haierosion Hau rate of coast 8.3 became myr the(Tran main et al., eroded 2001). coastline with an average Ly Mouth based on the analysis of “weak” (less than 2.5 myr 10 myr was 59 km, with a meancovering intensity covering 45.5 45.5 %. % For of the theto shoreline period and 25.5 1991–1995, a km strong the intensity due lengthVan to of Uc eroded dike River coastline mouth) consolidation decreased and anderosion Tien because Lang to (southwest sections accretion. of in However, Van strong Bang Uc intensity River La mouth) covered (northeast switched up from of to 87.5 % of the shoreline a southern direction anderosion do also not takes reach place north theintensity. of coastline The the of reduction Van the Uc of Riverthe Hai sediments (Haiphong HBD Hau exported city) has district. although to already with Shoreline thecoastal been lower coastal line identified (Tran zone as et due al., the to 2002; main Do trapping cause et in of al., intensified 2007, erosion 2012). in RRD Bergh et al., 2007a). Sediments from the Red River (Ba Lat) are largely transported in 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ects of tides ff Cs Radiotracer, , 2005. 137 Pb and ciency criteria for hydrological 210 ffi erent e ff 10.5194/adgeo-5-89-2005 358 357 ects of climate and anthropogenic change on small ff This work was financed by the science and technological cooperation pro- Hydrological regime and waterEarth budget Sci., of 37, the 219–228, Red 2010. River Delta (Northern Vietnam), J. Asian réton, J. P.: SeasonalEstuary, variability Haiphong of (Vietnam), Geo-Mar. cohesive Lett., sediment 32, aggregation 103–121, 2012. in the Bach Dang-Cam budgets for the Red2005. River basin (Vietnam and China), Global Biogeochem.sediment Cy., load 19, of the 1–16, Red River, Viet Nam, J. Hydrol., 334, 199–214, 2007. model assessment, Adv. 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Lat, prodelta (Red River, Viet Hoa Binh hydropower dam onSci. the coastal Technol., 3, sedimentary 1–17, environment 2008. in red river delta, J. Mar. sediment in a partly mixed estuary, Estuar. Coast. Shelf S.,intrusion 20, length, 147–167, tidal 1985. range and residence time, Cont. Shelf Res., 22, 1835–1856, 2002. impacts on coastal changes in Vietnam, Reg. Environ. Change, 4, 49–62, 2004. Vu, D. V., Nguyen, D. C., and Tran, D. T.: The impact of Hoa Binh Dam on distribution of sus- Verney, R., Lafite, R., and Brun-Cottan, J. C.: Flocculation potential of estuarine particles: the Yang, Z., Wang, H., Saito, Y., Milliman, J. D., Xu, K., Qiao, S., and Shi, G.: Dam impacts on van Rijn, L. C.: Principles of Sediment Transport in Rivers, Estuaries and Coastal Seas, Aqua Wang, H. J., Yang, Z. S., Wang, Y., Saito, Y., and Liu, J. P.: Reconstruction of sediment flux van Maren, D. S. and Hoekstra, P.: Seasonal variation of hydrodynamics and sediment dynam- van Maren, D. 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O.: Regimes of human and climate 5 5 15 30 10 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ), and coef- 1 − 364 363 (1960–1979) (1989–2010) Dry Rainy total year Dry Rainy total year ) 2.76 22.28 29.25 5.77 23.58 33.33 ) 16.26 86.91 116.08 18.18 75.18 105.80 ) 6.64 42.82 54.49 9.81 39.48 55.54 ) 4.18 17.92 25.14 4.50 18.54 26.29 ) 4.40 22.14 30.08 5.77 22.91 32.34 3 3 3 3 3 t) 0.46 26.07 28.93 0.74 19.17 21.57 t) 3.27 108.55 119.26 1.91 40.32 46.13 t) 0.64 62.36 64.98 0.33 5.17 5.76 t) 1.95 38.66 43.45 1.40 46.43 51.74 t) 0.18 8.33 9.22 0.35 11.62 12.68 m m m m m 6 6 6 6 6 9 9 9 9 9 10 10 10 10 10 10 10 10 10 10 × × × × × × × × × × ( ( ( ( ( M( M( Q M( Q M( Q M( Q Q 1 2 3 4 5 6 7 8 9 10 11 12 CV (%) average Average water and suspended sediment fluxes measured at five gauging stations Average monthly and annual suspended sediment concentration (mg L 1989–2010 32.91989–2010 30.3 324.31989–2010 270.8 40.1 314.2 35.2 80.7 523.11989–2010 31.4 1012.7 101.2 216.4 2339.91989–2010 30.1 93.9 378.4 3150.2 123.1 30.9 91.9 2990.7 100.8 474.8 117.0 2611.4 131.4 41.2 399.2 1413.7 146.3 262.2 255.1 1041.0 351.0 91.4 427.1 317.3 191.0 717.1 153.1 480.1 77.5 71.0 857.4 141.6 606.0 2058.2 875.6 36.0 577.1 87.5 772.8 338.3 88.1 52.0 531.2 252.2 421.4 36.9 365.3 96.8 138.7 32.1 68.3 72.8 70.0 397.4 737.6 105.7 Duong 5 Red 4 Da 3 Thao 2 Lo 1 River Station Parameter Before Hoa Binh Dam After Hoa Binh Dam Lo 1960–1979 24.1 25.1 46.7 66.8 328.6 484.7 444.0 399.4 255.3 151.1 69.4 29.5 92.2 306.5 River PeriodThao 1960–1979Da 404.8 382.2Red 1960–1979 417.7 549.7 45.6 1960–1979Duong 920.7 183.3 1960–1979 45.6 163.6 125.8 1804.9 34.9 156.3 118.9 2426.1 265.5 211.5 103.9 2908.8 196.8 439.1 2001.2 538.9 1225.2 556.7 1249.1 1014.0 1787.9 868.0 1383.1 1028.4 1792.4 1468.4 1291.1 521.6 1068.6 1369.8 978.8 80.2 1025.2 726.2 509.0 Monthly 713.3 averages 1728.5 484.9 319.3 452.4 224.6 92.5 180.8 74.0 111.9 79.6 1027.4 1192.7 989.2 Annual Table 2. ficient of variation ofafter (1989–2010) mean Hoa monthly Binh values, Dam at impoundment. five gauging stations before (1960–1979) and Table 1. during the dry season (December–April), the(1960–1979) rainy and season (June–October), after and (1989–2010) per year, HoaFig. before 1). Binh Dam impoundment (see locations of stations in Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Luu et al. a 366 365 dry rainy total dry rainy total season season year season season year t) 2.61 77.26 84.85 1.66 30.52 35.14 t) 0.09t) 4.81 0.14t) 5.16 7.43 0.06t) 7.96 2.79 0.28 0.11t) 2.99 10.65 0.12 2.10 0.17t) 11.54 2.43 4.72 0.26 3.10 0.07t) 0.24 5.10 3.57 6.40 0.78 1.13t) 4.40 7.12 19.00 1.30 0.19 0.10t) 5.07 21.12 4.59 0.69 1.95 0.13 0.37 5.10 16.87 2.24 2.35 18.76 6.81 2.70 0.09 7.84 0.38 1.71 6.97 1.97 8.02 dry rainy total dry rainy total 2006 1996 6 6 6 6 6 6 6 6 6 6 season season year season season year (dry year) (wet year) 10 10 10 10 10 10 10 10 10 10 ) 4.45) 21.16 17.76 28.84 98.76 130.50 4.82 20.78 19.53 85.22 27.62 120.28 ) 0.79) 6.39 1.22) 7.96 9.84 0.45) 12.25 3.67 2.06 1.39 13.89 4.57 2.05) 6.00 17.76 0.89 7.98) 8.37 0.74 2.94 6.16 11.47 1.68) 3.21 12.46 7.84 8.04 5.01) 4.48 17.45 10.94 23.85 1.21 1.31 32.5 5.76 1.63 5.54 7.84 6.60 4.72 7.75 19.11 9.33 1.18 27.03 4.79 6.78 3 3 3 3 3 3 3 3 3 3 × × × × × × × × × × m m m m m m m m m m ( ( ratio (%)( 3.45ratio (%)( 6.23 5.36ratio (%)( 6.08 9.62 2.30ratio (%)( 9.38 10.73 3.61 6.63ratio (%) 13.78( 3.52 10.24 4.60 6.88ratio 13.60 (%)( 10.16 6.92 6.11 9.96 4.22ratio (%) 14.46 10.16 ( 6.01 29.89 8.28 3.70 14.42ratio (%) 24.59 14.43 ( 8.39 3.70 7.28 6.02ratio 24.89 (%) 26.44 5.94 6.39 7.83 22.29 21.84 6.01 6.37 7.70 22.31 22.11 22.31 7.68 5.42 22.89 5.60 22.84 22.82 5.61 9 9 9 9 9 9 9 9 9 9 10 10 10 10 10 10 10 10 10 10 delivery (1960–1979) (1989–2010) M M M M M M M M M M M M M M M M M M M × × × × × × × × × × (%)( ratio (%) 49.49( 25.06 44.36 21.43 45.30 22.10 42.54 23.20 42.29 22.92 42.31 22.96 52.0 22.0 44.7 20.8 56.7 17.2 ( ratio (%)( ratio (%) 4.45( ratio 6.47 (%) 6.87( ratio 6.10 9.96 (%) 2.53ratio (%) 11.60 9.39 3.72 6.69( 25.45 14.06ratio (%) 3.50 7.04 9.87( 34.21 13.61ratio (%) 5.01 32.60 6.96 9.36 3.56( 14.15ratio 6.24 (%) 9.46 9.54 34.26 3.77 14.62( ratio 28.21 6.01 8.14 (%) 34.79 14.51 3.72 24.15 34.73 8.38 6.81 6.30 24.90 26.0 5.83 6.50 7.84 22.71 34.6 6.01 6.44 7.74 22.42 22.47 26.1 11.0 7.76 5.68 25.0 10.0 5.62 5.64 6.0 delivery (1960–1979) (1989–2010) (2005) (2010) Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Average suspended sediment fluxes in the nine distributaries of the Red River in the Average water discharge in the nine distributaries of the Red River in the dry season Total River mouth Sediment before Hoa Binh DamBach Dang Cam after Hoa Binh Dam Lach Tray Van Uc Thai Binh Tra Ly Ba Lat Ninh Co Day Pruszak et al. (2005). River mouth Water before Hoa Binh Dam after Hoa Binh Dam P Sub-Total Center Day Total Bach Dang Cam Lach Tray Van Uc Sub-Total NE Thai Binh Tra Ly Ba Lat Ninh Co a Table 4. dry season (December–April), the1979) rainy and season after (June–October), (1989–2010) and Hoa Binh per Dam year, impoundment. before (1960– Table 3. (December–April), in the rainy seasonafter (1989–2010) (June–October), Hoa and Binh per Dam year,et impoundment; before al., comparison (1960–1979) 2005; with and Luu previous et estimates al., (Pruszak 2010). Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

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-1 3 -1 3 Annual water and sediment discharge in the main tributaries of the Red River system Comparison of modeled and measured water discharge ( concentration ( Fig. 3. after calibration of the model. Fig. 4. (1960–2010), and average values before and after Hoa Binh Dam impoundment.