Simulation of River Bed Degradation with Bed Rock Erosion Downstream of the

Sumi, Tetsuya University of Kyoto, Kyoto, Japan [email protected]

Lai, Jihn-Sung, Lee, Fong-Zuo, Tan, Yih-Chi & Huang, Chen-Chia National University, City, Taiwan

ABSTRACT:

After the completion of a or a weir, coarser sediments could be trapped in the impounding water area. Part of inflowing sediment tends to deposit during reservoir operation. Over a period of time, the downstream river bed may gradually be degraded by the released flood flow which contains less sediment supply than that of reservoir inflow. River bed erosion caused by running flood may create problems of scouring the foundation of levees or bridge piers. In Taiwan, several river reaches downstream of the have the bed rock erosion problems that possess of complex mechanism. The hydraulic erosion and sediment abrasion are studied to estimate the degradation of bed rock. The numerical mobile-bed model is adopted to simulate erosion phenomena downstream of the Shihmen reservoir. The Shihmen Reservoir has the function of water supply for municipal and agricultural demand in the northern part of Taiwan. The Shihmen Reservoir is situated in the Dahan creek that is one of the major tributaries of the Tanshui River. In this research, the degradation tendency is investigated using bed rock erosion formulas. The simulated results provide further understanding of bed degradation mechanism.

Keywords: Degradation, Bed rock, Erosion mechanism

1. GENERAL INSTRUCTIONS in channel capacity and specific discharge time series are explicitly simulated. Similar to the 1D model of In Taiwan, many downstream alluvial rivers of Greimann and Vandeebrg (2008), the 2D model would and dams are characterized by the presence and exposure not estimate the local erosion caused from plunging jets of soft rocks on the river bed, due to lack of sediment downstream of spillways. Such erosion could be supply. The soft rock consists of mainly mudstone and estimated using models developed by Bollaert and sandstone which is relatively weak (shear strength lower Schleiss (2005) and Annandale (2006). Bolaert and than 25.0 MPa) and subject to essential erosion during Mason (2006) applied the method of Bollaert and high flows. Therefore, soft rock erosion is an important Schleiss (2005) to estimate scour in a plunge pool river process in Taiwan. For example, a few kilometres downstream of a dam. Therefore, this study would not of river channels downstream of the Chi-Chi Weir, apply such techniques similar to Annandale (2006) to Shihkang reservoir and Shihmen reservoir have estimate local rock scour downstream of dams; experienced up to couple meters of rock scour since weir representative applications and procedures are reported and reservoir construction (see Fig. 1). Much bed rock by Frizell (2006; 2007). Besides, Sklar and Dietrich erosion is the result of interaction of hydraulic erosion (2004) and Lamb et al. (2008) researched on the abrasion and sediment abrasion. There are many researches of erosion. Sklar and Dietrich (2004) considered the bedrock erosion and are usually classified to hydraulic abrasion erosion from bed load effect and Lamb et al. and abrasive scour kinds. Tomkin et al. (2003) compared (2008) further considered suspended load influence and various empirical models for bedrock erosion, but, the combining bed load effect to simulate bed rock erosion. results showed that they generally cannot explain However, in this study, only bed load effect is employed observed behaviour because of the simple empirical to estimate due to simplify model routing. approaches do not account for the varying channel capacity in different parts of the river and they account Water Resources Planning Institute (2009) already used for the distribution of discharge with time. Therefore, in the same method to verify parameters of bed rock erosion this study, building a bedrock erosion module into 2D phenomenon. But, unfortunately, many bed rock erosion hydraulic and sediment transport models, the variations phenomena, mechanisms and rates do not agree with each domestic environment. Therefore, this study the Shihmen reservoir has accumulated a significant chooses exposed bed rock area in the downstream of amount of sediment after dam completion. The Shihmen reservoir in at northern Taiwan for depositional pattern has become wedge-shaped since the application case. Using of the hydraulic scour and 2000. sediment with rock abrasion in bed rock erosion model From identification by the parameters of the turnover rate for parameter identification and verification. Then, the of water(CAP/MAR=total capacity/Mean annual runoff) study would establish appropriate bed rock parameters in and sediment(CAP/MAS=total capacity/Mean annual Dahan River and recognize which erosion mechanism inflow sediment) (Sumi, 2011), the life of Shihmen would dominate bed rock erosion in Shihmen reservoir reservoir is reduced from 188 year to 55year due to area. Chi-Chi earthquake effect (Fig. 3). Fig. 4 show the variation of deposition volume from reservoir is constructed. The mainly deposition volume happened in 1964 year and 2004 year after reservoir is constructed and typhoon AERE attacking, respectively. The Fig. 4 (a) also shows that the Chi-Chi earthquake does not affects deposition volume obviously in recent 10 years. Therefore, the mainly deposition volume is result from typhoon effect. Based on recent survey data in 2010, the storage capacity was estimated to be 67.07% of its initial (b) capacity.

Fig. 5 shows the cross sections below the Shihmen reservoir and Fig. 6 shows the mainly variation area of bed elevation from section 86 to section 90. According to (c) the degradation of section 90, there is about 9m be eroded after Shihmen reservoir is constructed. However, Figure 1. Photographs showing exposed bed rock at the starting year of bed rock erosion is not recorded downstream of (a) Chi-Chi weir (b)Shihkang reservoir clearly. But, based on 2004 field survey of Northern (c)Shihmen reservoir Water Resources Bureau, bed rock is exposed and mainly exposed area was from section 90A to section 82. Therefore, the bed elevation of 2004 was adopted as a 2. DESCREPTION OF SHIHMEN RESERVOIR initial geographic condition to simulate bed rock erosion. DOWNSTREAM

The Shihmen reservoir is a multi-functional reservoir and its functions include irrigation, water supply, generating electric power, preventing flood and recreation. The Shihmen reservoir has a natural drainage area of 762.4 km2. It is formed by the Shihmen dam located at the upstream reach of the Dahan River. The Dahan River is one of the three tributaries of the Tamshuei River which flows westward the Taiwan Strait. A map of the watershed area of the Shihmen reservoir is presented in Fig. 2. The Shihmen dam was constructed in 1963 is a 133.1m high embankment dam with spillways, Figure 2. Watershed of Shihmen reservoir (Lee et al., 2007) permanent river outlet, and power plant intake and flood 100000 diversion tunnels controlled by tailrace gates. The Excavation(before Chi-Chi earthquake) Excavation(after Chi-Chi earthquake) Dredging(before Chi-Chi earthquake) Dredging(after Chi-Chi earthquake) elevations of the crest, permanent river outlet, Venting(before Chi-Chi earthquake) Venting(after Chi-Chi earthquake) and power plant intake and tunnel spillway are EL.235 m, 10000 Others(before Chi Chi earthquake) Others(after Chi-Chi earthquake)

EL.169.5m, EL.173m and EL.220m, respectively. The 1000 total discharge of spillways is 11400m3/s, permanent Shihmen river outlet is 34m3/s, power plant intake is 137.2m3/s 100 and tunnel spillway is 2,400m3/s. With a maximum water 10 Shihmen level of EL.245 m, the reservoir pool is about 16.5 km in

2 Life=CAP/MAS Reservoir length and forms a water surface area of 8.15 km . The 1 initial storage capacity was 30,912x 105 m3, and the 5 3 0.1 active storage was 25,188x 10 m. Due to a lack of 0.0001 0.001 0.01 0.1 1 10 sufficient desiltation facilities, incoming sediment Capacity-inflow ratio=CAP/MAR particles have settled down rapidly along the reservoir since the dam was completed. Based on the survey data, Figure 3. Reservoir characteristics in Taiwan 40 120 1999  c Before Chi‐Chi‐Earthquake AfterChi‐Chi‐Earthquake n ) )

3 (1) 35 3 E  k pU ( 1) (1 )  Ea m m 6 33% of 100 6  cri ctr 30 Capacity Where, E =total rock erosion rate (m/s), k =hydraulic 25 Typhoon 80 p Aere(2004) 20 erodibility, U =depth averaged flow velocity (m/s), 60 First year after reservoir 15 constructed  ,  cri =bed shear stress ; critical shear stress for 10 40 hydraulic scour (Pa), c , c =thickness of rock cover ; 5 tr 20 0 transition thickness (m); n =empirical exponent and Accumulative deposition volume(10 deposition Accumulative Average annual depsition volume(10 depsition annual Average

-5 0 Ea =abrasive scour rate (m/s). The first term on the right 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 hand side of equation (1) represents the hydraulic scour Year rate and it is set to be a function of the stream power (τU) Figure 4. Variation of sedimentation in Shihmen reservoir (Annandale,2006). The above form has the advantage of being dimensionally consistent as opposed to the dimensional equations used in many existing models such as that of Tomkin et al. (2003) and it is also consistent in form to the cohesive sediment transport Section 90A Section 90

Section 89 relationships. The c / ctr term represents the armour Section 88 Section 87 effect and ctr  0.1m was used as the transition Section 86 thickness above which zero rock erosion is expected. Section 85 Besides, n=1 is used in this study as no concrete data Section 84 Section 83

Section 82 Section suggest the use of nonlinear relations. Therefore, two empirical parameters are needed for the hydraulic scour:

k p and  cri . The dimensionless erodibility parameter k can be a calibration parameter in the numerical model Figure 5. Mainly bed rock area and cross sections p and it is also probably can be a site specific value. Based

129 Section 86 on the results of Greimann and Vandeburg (2008) and 126 123 Section 87 Water Resources Planning Institute report (2009), the 120 -6 117 Section 88 value of k is set from 4.0*10 to 1.0 downstream of 114 p elevation(m)

111 Section 89

108 Bed Section 90 the weir if abrasive scour is ignored. In this research, the 105 ~9m

102 ~102m 1969 1970 1980 1990 2000 2007 2010 same value is adopted. The critical stress  may be Year cri estimated using the Annandale (2006) approach, field test, or numerical model test in comparison with field Figure 6. Variation of bed elevation at each cross section data. With the Annandale method the critical stream power may be related to the critical shear stress as (Greimann and vandeburg, 2008). According to the 3. DESCREPTION OF BED ROCK EROSION calibration results of Water Resources Planning Institute MODEL AND SIMULATED CONDITION report (2009) in Chu-Chi weir and Shihkang reservoir,

the value of  cri is between 100 Pa and 300 Pa. In this study, we employed that the hydraulic scour and Therefore, this study also follows such range in Shihmen abrasive scour be modelled separately to simulate bed reservoir. rock erosion. And, mainly content is following the results of Water Resources Planning Institute report (2009). The abrasive scour is based on the model of Sklar and Therefore, both models are incorporated into 2D mobile Dietrich (2004) and adopted model is presented as bed model. Field survey should be conducted to following: determine whether the study site is hydraulic scour 1.5 dominant, abrasive scour dominant, or both play 0.08R gY   u  E  b q ( 1)0.5 1 ( * )2 F (2) important roles. Model simulation results may also be a 2 s   e kv T  c  wf  used through post-analysis to assess the dominant scour   mechanism. In which Ea =abrasive scour rate (m/s),

R b = s /  1, s =is sediment density and ρ is water The presented rock erosion model follows the results of 2 density, g=gravity (m/s ), k =rock erodibility parameter Greimann and Vandeburg (2008) with minor v modifications. The rock scour rate is computed by (-), Y=modulus of elasticity of rock (Pa),  T =tensile combining both the stream power based hydraulic scour strength of rock (Pa), qs =sediment supply per unit width model with excesses shear tress and the bed load abrasive scour model as follows: (kg/m/s), , c =bed shear stress and critical shear stress (Pa), wf =sediment fall velocity (m/s),u* =shear velocity 2758000 2758000 Yuanshan Weir (m/s) ;  /  and Fe =fraction of exposed bedrock. 2756000 2756000

Section 82 2754000 2754000 Bed elevation (m) There are three parameters needed to be determined for 140

y(m) 2752000 130 y(m) 2752000 120 110 abrasive erosion: k , Y and  . k is a dimensionless Section 82 Section 82 v T v 100 2750000 2750000 90 80 parameter representing rock erodibility and it may be 70 60 2748000 2748000 Obviously 50 estimated in the laboratory that presented by Sklar and Section 90A bed rock area 40

2746000 2746000 Dietrich (2004), but it needed to be calibrated for field 276000 278000 280000 282000 284000 286000 276000 278000 280000 282000 284000 286000 Section 90A applications. Based on the calibration results of Chi-Chi x(m) x(m) weir and Shihkang reservoir, its value was calibrated to be from 10 to 1000 at different cross sections if only Figure 8. Simulation mesh and initial bed elevation in 2004 abrasive scour is present. Y is the rock modulus of elasticity (Pa) and is the rock tensile strength (Pa). T 4. SIMULATION RESULTS AND DISCUSSION Based on the relative values in similar locations, Y and

can be measured in the field. Note that, the fraction of  T Due to the lack of field test, the hydraulic erosion and the exposed bed is represented by Fe in the abrasive abrasion erosion parameters from refer to the values of model equation (2). In addition, it can be chosen the Shihkang reservoir and Chi-Chi weir (Water Resources same as the hydraulic scour, i.e. F 1- c / c . However, Planning Institute report, 2009). Table 1 lists the e tr reference data from Shihkang reservoir area and Chi-Chi F  1- q / q is used to represent the fraction of bedrock e s t weir area and calibrated values of k , Y, , k and exposure with the sediment transport capacity per unit v T p cri width (kg/m/s). from 2004 year to 2006 year in this study. The calibrated

values indicated that k v ,  T and  cri at same order On the other hand, the sediment transport equation of between three areas. But, Y and k presented couple Parker (1990) was adopted. Besides, due to the initial bed p condition is from 2004 year, the simulated boundary order difference, especially Y. Therefore, the value of condition is also from 2004year. Fig. 7 shows the Y needed to measure in the field to adopt proper value. hydrograph of boundary condition and combines Fig. 9 shows the variation of bed elevation from 2004 apparently hydrological events from 2004 year to 2008 year to 2006 year and the figure also shows the bed year to simulate bed rock erosion. The first part from elevation tendency of downstream river is erosion, 2004 year to 2006 year was used for calibration especially at section 78 and section 75. However, the parameters and from 2006 to 2008 year was used for erosion area of field survey presents cross section erosion verification duration. Fig. 8 presents the simulation mesh performance between section78 and section 87 and and initial bed elevation from section 90A of upstream simulated result presents mainly channel erosion boundary and Yuanshan weir of downstream boundary. phenomenon. Fig. 10 shows the comparison of The simulated mesh was locally increased to improve measurement data and simulation results at section 85, simulation accuracy. section 87 and section 89. Mainly part of each cross 5500 section was choosing for comparison. The figure shows 5000 Section 90A 實測值 4500 the fine agreement results at main channel of section 85 4000

3500

/s) and section 89, except section 87. The simulation results 3000 3

2500 Q(m indicated that employed model can deal with mainly bed 2000 1500 rock erosion at deep channel, but, weakly simulate at 1000 檢定(85 hr) 驗證(138 hr) 500 2004~2006 2006~2008 flood plain or widely cross section. Integrated to say, the 0 0 25 50 75 100 125 150 175 200 225 20000 時間 檢定(85 hr) (hr) 驗證(138 hr) bed rock tendency can preliminary describe by presented 18000 2004~2006 2006~2008 16000 model, but, precisely erosion depth and range is needed 14000 Section 90A 12000 to improve. Fig. 11 shows the variation of bed elevation 10000

8000 from 2006 year to 2008 year and the figure also shows

6000

4000 the bed elevation tendency of downstream river is Sediment concentration (ppm) concentration Sediment 2000 實測值 erosion as 2004 year to 2006 year, especially at section 0 0 25 50 75 100 125 150 175 200 225 51.9 78 and section 75 downstream. However, the erosion 51.8 2004~2006檢定(85 hr) 2006~2008驗證(138 hr) 51.7 area of field survey obviously presents cross section 51.6 51.5 erosion performance between section 75 and section 87 51.4 51.3 and simulated result still presents mainly channel erosion 51.2

51.1 Wa ter level (m) phenomenon. Fig. 12 shows the comparison of 51.0 實測值 50.9 Yuanshan Weir measurement data and simulation results at section 85, 50.8 0 25 50 75 100 125 150 175 200 225 Time (hour) section 87 and section89. Mainly part of each cross section was also choosing for comparison. The figure Figure 7. Boundary conditions of inflow and outflow shows that the relative fine agreement results at main channel of section 85, section 87 and section 89. Based on the field survey at section 87 from 2004 to 2008, the 120 Section 85 115 Simulation (2006) variation during 2004 to 2006 is erosion but during 2006 Measurement(2006) 110 to 2008 is deposition. The simulation results pointed out (m) Initial elevation(2004) adopting model can deal with mainly bed rock erosion at 105 模擬值(95年) deep channel and also sedimentation mechanism at flood 底床高程 100 實側值(95年) Bed elevation (m) elevation Bed 95 plain or widely cross section if those sections possess 初始底床(93年實測值) sedimentation and bed rock erosion at the same event. 90 0 100 200 300 400 500 600 120 The results also presented that the sediment transport Section 87 距左岸距離(m) 118 模擬值(95年) 116 equation of Parker (1990) is suitable in Dajia River, 實側值(95年) 114 Chosui River and Dahan River. Overall to say, the bed 初始底床(93年實測值) (m) 112 rock tendency can preliminary describe by presented 110 108 model, but, precisely erosion depth and range is needed 底床高程 106 to improve. (m) elevation Bed 104 102 100 270 320 370 420 470 130 距左岸距離(m) Section 89 Table 1 Relative parameters of bed rock erosion 模擬值(95年) 125 Critical 實側值(95年) Modulus of Erodibility Tensile Hydraulic 初始底床(93年實測值) shear (m) 120 Sections elasticity parameter strength erodibility stress Y (Pa) KV σT (Pa) KP 2 115 τcri (N/m ) 底床高程

Shihkang Reservoir Area (Dajia River) (m) elevation Bed 110 6 6 -6 7*10 50 5*10 4*10 200 105 Chi-Chi Weir Area (Chosui River) 0 50 100 150 200 250 300 350 400 Distance距左岸距離 from left(m) bank (m) 6 6 -6 7*10 75 5*10 1*10 225 Shishmen Reservoir Area (Dahan River) Figure 10. Mainly comparison of bed elevation from 2004 85~82 5*1010 50 1*106 4*10-6 200 year to 2006 year in section 85, section 87 and section 89 87~85 1*1011 50 1*106 7*10-7 200 88~87 5*1010 50 1*106 7*10-7 200 2758000 90A~88 5*109 50 1*106 7*10-7 200 Section 72 2756000 2758000 Section 75

2754000 Section 72 2756000 Section 78 Section 78A Section 75 2752000 y(m) Change of bed elevation (m) 2754000 Section 82 -0.5 Section 78 -1.0 Section 78A 2750000 -1.5 -2.0 2752000 -2.5 y(m) Change of bed elevation (m) Section 85 -3.0 -3.5 -0.5 Section 87 Section 82 2748000 -4.0 -1.0 Section 88 -4.5 -1.5 2750000 Section 89 -5.0 -2.0 Section 90 -2.5 Section 85 -3.0 2746000 -3.5 276000 278000 280000 282000 284000 286000 2748000 Section 87 -4.0 x(m) Section 88 -4.5 Section 89 -5.0 (a) Section 90 2746000 276000 278000 280000 282000 284000 286000 x(m) (a) 2758000

2758000 2756000 Change of bed elevation (m) -0.5 Section 75 -1.0 2756000 2754000 -1.5 Change of bed elevation (m) Section 78 -2.0 -0.5 Section 78A -2.5 Section 75 -1.0 -3.0

y(m) 2752000 2754000 -1.5 -3.5 Section 78 -2.0 -4.0 Section 78A -2.5 Section 82 -4.5 -3.0 -5.0

y(m) 2752000 2750000 -3.5 -4.0 Section 85 Section 82 -4.5 2750000 -5.0 2748000 Section 87 Section 88 Section 89 Section 85 Section 90 2748000 Section 87 2746000 Section 88 276000 278000 280000 282000 284000 286000 Section 89 Section 90 x(m) 2746000 (b) 276000 278000 280000 282000 284000 286000 Figure 11. Change of bed elevation from 2006 to 2008 (a) x(m) (b) Field survey (b) Simulation result Figure 9. Change of bed elevation from 2004 to 2006 (a) Field survey (b) Simulation result 120 模擬值(97年) Y, and to be a new parameter is probably Section 85  T k v 115 Simulation (2008) Measurement(2008) 實側值(97年) attempted to try. In addition, the abrasion erosion in this 110 Initial elevation(2006)實側值(95年) (m) study only considered bed load effect. Therefore, 105 combing bed load and suspended load effect was

底床高程 100

Bed elevation (m) elevation Bed reasonable to improve simulation accuracy and the 95 scheme of Lamb et al. (2008) is a good method to replace 90 0 100 200 300 400 500 600 the equation of Sklar and Dietrich (2004) in this study. 120 Section 87 距左岸距離(m) 118 模擬值(97年) 116 實側值(97年) 114 實側值(95年) (m) 112 ACKNOWLEDGEMENT 110 The presented study was financially supported by the Water 108

底床高程 106 Resources Planning Institute, Water Resources Agency

Bed elevation (m) elevation Bed 104 Ministry of Economic Affairs. Writers wish to thank the 102 100 National Taiwan University Hydrotech Research Institute and 270 320 370 420 470 130 Disaster Prevention Research Institute of Kyoto University in 距左岸距離(m) Section 89 模擬值(97年) Japan for manpower and technique supporting. 125 實側值(97年) 實側值(95年) (m) 120 REFERENCES 115

底床高程 Bed elevation (m) elevation Bed 110 Annadale G.W. (2006) : Scour technology, mechanics and

105 engineering practice.” McGraw Hill, New York. 0 50 100 150 200 250 300 350 40 Bollaert, E.F.R., and A. J. Schleiss (2005) : Physically Based Distance from距左岸距離 left bank(m) (m) Model for Evaluation of Rock Scour due to High-Velocity Jet Impact, Journal of Hydraulic Engineering, 131(3), Figure 12. Mainly comparison of bed elevation from 2006 pp.153-165. year to 2008 year in section 85, section 87 and section 89 Bollaert, E.F.R., and Mason, P.J., (2006) : A Physically Based Model for Scour Prediction at Srisailam Dam, Hydropower and Dams, Issue Three. 5. CONCLUSIONS Frizell (2006) : Hydraulic Investigations of the Erosion Potential of Flows Overtopping Gibson Dam, Sun River In past 10 years, the downstream river bed gradually be Project, Montana, Great Plains Region, Hydraulic Laboratory Report HL-2006-02. US Bureau of Reclamation. degraded by the released flood flow after reservoir or Frizell (2007) : Analysis of the Erosion Potential of Flow weir was constructed and the gradation reason result Overtopping Arrowrock Dam, Technical Memorandum No. from less sediment supply that of reservoir outflow in ARR-8560-IE-2007-1 US Bureau of Reclamation. Taiwan. Over a period of time, the remained sediment at Greimann, B.P., and Vandeberg, M., (2008) : Predicting Rock the downstream would be flushed out to the sea and bed Scour, Technical Report SRH-2008-01, Technical Service rock would finally expose. This study focuses on the bed Center, Bureau of Reclamation, Denver, CO. rock erosion with hydraulic mechanism and sediment Lamb, M.P., Dietrich, W.E., and Sklar, L.S. (2008). “A Modle abrasion methods in Shihmen reservoir downstream. Five ofr Fluvial Bedrock Incision by Impacting Suspended and parameters were pointed out, three of them (Y, Bed Load Sediment.” J. Geophys. Res., 113, F03025.  T Lee, F. Z., Lai, J. S., Hwang G. W. and Tan, Y. C. (2007) : Influence of High-turbid Inflow on Irrigation and Water and cri ) can be measured and specified from field test Supply in the Shihmen reservoir, 2007_58th ICID IEC and two of them ( k v and k p ) needed to calibrate from Meeting and Fourth International Conference on Irrigation calibration and verification. According to the historical and Drainage. data and field survey, it is realized that bed rock exposed Parker, G. (1990) : Surface-Based Bedload Transport Relation from 2004 year. Therefore, from 2004 year to 2008 year for Gravel Rivers, J. Hydraulic Research, 28(4), pp.417-436. Sklar, Leonard S., and William E. Dietrich (2004) : A was separated as calibration period and verification mechanistic model for river incision into bedrock by saltating duration. The simulation results show that the simulated bed load,” Water Resources Research, Vol. 40, No. 6, pp bed rock tendency can preliminary describe by presented 063011-0630121. model, but, precisely erosion depth and range is needed Sumi, T. and Kantoush, S. A. (2011) : Comprehensive to improve. Besides, the adopted sediment transport Sediment Management Strategies in Japan: Sediment bypass equation of Parker (1990) is suitable to use in Dajia tunnels, 34th IAHR World Congress, pp. 1803-1810, River, Chosui River and Dahan River. According to the Brisbane, Australia. simulation results of Shihmen reservoir downstream, the Tomkin, J. H., Brandon, M. T., Pazzaglia, F. J., Barbour, J. R. bed rock erosion parameters are calibrated to Y is from and Willet, S.D. (2003) : Quantitative Testing of Bedrock 9 11 Incision Models for the Clearwater River, NW Washington 5*10 to1*10 , k v is equal to 50,  T is equal to State, Journal of Geophysical Research, 108(B6), 2308, 1*106, k is from 4*10-6 to 7*10-7 and is equal to pp.1-19. p cri Water Resources Planning Institute, Water resources agency, 200. Moreover, due to the obviously difference of Y Ministry of Economic Affairs (2009) : Rock Erosion between field survey and simulation result, combining Modeling on Selected Alluvial Rivers in Taiwan, Bureau of Reclamation, U. S. A..