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A Study on Sediment Settling Pattern in the Reservoir of Shahid Rajaie by Using Observed Data & Empirical Methods

Zohreh Zargaran M.Sc. Student of Water Resources Engineering and Management, Islamic Azad University, Science & Research Branch, Tehran, [email protected]

Farhang Behrangi Ph.D. Candidate in Hydraulic Structures, School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran [email protected]

Leila Amiri Ph.D. Candidate in Environmental Engineering, Department of Civil and Environmental Engineering, K.N.Toosi University of Technology, Tehran, Iran [email protected]

Abstract

In addition to reducing the useful storage capacity, sedimentation in reservoirs makes changes to a river basin and reservoir morphology. Depending on the amount of incoming sediment, trap coefficient and the manner of settling, the useful life of the reservoirs varies. With the movement of sediments towards the body of the dam and the obstruction of the discharging gates and turbine valves, the dam operation will practically face problems. Therefore in sedimentation studies, besides the incoming sediment, its movement rate towards the body of the dam, and the sediment deposit procedure must be taken into account. This paper presents a study on Shahid Rajaee reservoir in Iran in which first, by using AutoCAD Civil 3D 2011 software, the geometrical information of the reservoir such as its volume, area and longitudinal profile are obtained from hydrographic maps. Then with observed data and empirical methods, the amounts of sediment inflow as well as its settling pattern in the reservoir are studied and the future of sedimentation procedure in this reservoir is anticipated.

Keywords: Shahid Rajaie Dam, Sedimentation, longitudinal profile, Hydrographic, Trap coefficient, Civil3D

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1. Introduction By constructing a dam, a lake will be created in its upstream. Because of water retrogression, the speed of river behind the dam decreases; as a result, the coarse sediments will deposit far from the structure and the fine particles which are easily carried by the flow eventually sink to the bottom of the reservoir near to the body of the dam. Problems created by deposition of sediment are numerous and varied. Sediment deposition in the dam reservoir is reflected in the reduction of the storage capacity of the reservoir. Moreover, the deposition is followed by a rise in water level which leads to an increase in evaporation in the lake as well as the inundation of the lands and the creation of swamps. Disturbance in discharging gate and a reduction in dam efficiency in controlling floods are among other disadvantages of sediment deposition. This paper will briefly discuss the researches upon sedimentation in reservoirs. It will also state literature reviews on Shahid Rajaie Dam as well as the target location of the present article. Afterwards, by using hydrographic maps of Shahid Rajaei reservoir and the observed data, the amount of deposited sediment is found. At this stage, the most popular and current empirical relations involved in the deposition of dam reservoirs are applied and their efficiency in the reservoir of Shahid Rajayi dam is identified. These relations include those estimating the volume of sediment inflow and the ones determining the reservoir trap coefficient. The rest of this article concerns with identifying the amount of deposit settling and studying its distribution pattern. According to the fore studies on this dam, it has been observed that there is no concern about the useful life of the dam in regard to the volume of sediment inflow. In this research, nevertheless, deposit settling and its pattern are studied by means of empirical relations, hydrographic maps and Civil3D software to make certain that the sediments do not strike the dam body and the valves (before reservoir is filled). In the end, a conclusion is drawn from the results, and reservoir future in respect to sedimentation is predicted and some suggestions for future studies are presented.

2. Literature reviews So far there have been many studies on sedimentation in reservoirs by scholars. Some of them are done by Numerical simulations of the river and reservoir of the dam. These studies have been performed by the implementation of soft wares such as HEC-RAS (Behrangi et al., 2009), GSTAR (Pourbojarian et al., 2009) and (Behrangi et al., 2011), HEC-6 (Gibson et al., 2004). The common point between these numerical models is that in all of them the amount of sediment inflow, the flow characteristics along with geometry of river and reservoir are considered as input and the output will demonstrate the manner of sediment distribution and deposition in different parts of the dam. Other sedimentation studies are performed by means of equations and empirical methods. These studies have also been done in two categories of anticipation of amount of sediment inflow and the manner of settling in reservoirs. In the studies concerned with the first category, (Behrangi et al, 2014) studied the sedimentation behind Latian Dam by means of empirical equations presented by different scholars, hydrographic results and hydrology statics. In this research, the strength or weakness of different empirical equations for Latian dam was examined and eventually by considering 85 MCM of useful capacity and 28 years of statics, the useful life of this reservoir was estimated as 96 years. (Pourbojarian et al, 2009) also investigated sedimentation behind Sefidrood Dam through usual empirical relations. In the second category of studies with the help of empirical relations, the manner of sediment deposit has been studied in two major forms. The first form, which is the most common, is the empirical methods of area- decrease and area-increase. In this research, (Shabanloo et al, 2002) studied the amount of sediment inflow and it’s settling pattern in the reservoir of . In this study on the basis of the amount of sediment inflow to the reservoir gained in 1983 and 1997, the amount and the manner of sediment deposit till 2021 were estimated. (Behrangi et al. 2009) in a study on Latian Dam reservoir also examined the accuracy of empirical methods by using actual values. In the recent study

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it was determined that Lara’s area- decrease method has been best suited for estimating the void capacity of the reservoir while in finding sediment deposits elevation near to the body of dam and close to the gates, area-increase method is the best. Also using area- increase and area- decrease method, Hasirchian et al. (2010) have also anticipated the manner of sedimentation settling in Shahid Rajaei Dam in future. The other form of relevant studies which are related is involved with longitudinal profile of the reservoir, formation of sedimentary delta and its movement towards the body of dam. In this area, Behrangi et al. (2008) have probed the formed delta in Latian Dam and demonstrated that of useful life of Latian reservoir comes to an end before the reservoir is filled with sediment and by Lavrak branch sedimentary delta conflux to the structure.

3. Location of the present research The present study is a research on sedimentation in Shahid Rajaei reservoir. In sedimentation studies, in addition to the amount of sediment inflow and sediment deposit in reservoir, the manner of settling distribution in different elevations and also the pace of sediment deposit progress towards the body of the dam are of great importance. (Ghaderi et al. 2010) by studying the abrasion amount of the reservoir basin of Shahid Rajaei dam indicated that an average of annually 0.25 MCM sediment enters the reservoir. Meanwhile, we can see this quantity is confirmed in reports prepared by the exploiting organization. Hence, considering the 162.5 MCM capacity of the reservoir, there shouldn’t be any concern about its filling with sediments. On the other hand, the manner in which the sediments fill the reservoir should be examined to prevent early obstruction before the reservoir is filled with deposit sediment. There are two ways achieving this goal. The first is area-increase and area-decrease method through which the volume of deposited sediments in various levels of the reservoir can be anticipated. This was done by (Hasrchian el al. 2010). In this study area-decrease proved better results and the sediment amount at different levels of the reservoir in future is anticipated. They predicted that the reservoir will have been filled with sediment by 2133. The significant point in all the studies made on Shahid Rajaei Dam reservoir is the lack of studies on the pace of the deposited sediment towards the body of the dam. So in present study this has been examined with empirical relations, the form of longitudinal profile, hydrographic maps and Civil3D software. In this study some empirical relations predicting the amount of sediment inflow and deposit sediment were also surveyed for Shahid Rajae Dam and the only ones which had more accuracy for the future of the region are presented.

4. Study area Shahid Rajaie dam is situated in a place named Tange-soleiman which is located in 40 kilometers from the south east of the city of Sari in Mazandaran province. It is constructed on Tajan River in the area to provide valuable irrigation water for the fertile agricultural lands in the downstream plains of the dam and to produce hydro-electricity, flood control and tourist attraction in the beautiful forests of Northern Iran. The dam is a double curvature concrete arch dam with 430 m crest length, 27 m width of dam in foundation and 7 m in crest. The height above foundation is 138 m and 116 m from the riverbed. The spillway manages 800 cubic meters of water per second and the area of its lake at normal water level is 158 cubic meters. Table1. indicates the other characteristics of the dam and the location of Shahid Rajaei dam is shown in Figure 1.

5. Meterials and methods Civil3D software This software was released by AutoCAD Company in April 2008. By combinig multiple advanced engineering softwares (e.g.,AutoCAD ،Land development ،Civil and HydroFlow ), this company presented a new advanced software named Civil3D which has particular usage in civil engineering branches specially in Hydrolic and road construction.

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By triangulating and computing the area of each triangle, Civil3D gives a good delicacy of surface area. The volume of the reservoir can also be obtained from its bed up to arbitrary elevation by computing the void volume between the horizontal plane and each tridimensional surface. Thus in each reservoir its area-volume-elevation diagram is attained (Pourbojarian et al, 2008).

Table 1. Empirical equations parameters value in Shahid Rajaee reservoir Parameter Value Unit Symbol Description A catchment area 1244 Km² Q Mean annual stream flow 11.04 m³/s HCM؟ 87875؟ C Initial storage capacity HCM؟ I The average annual inflow capacity 164568 R Topographic index 4.11

qw Annual runoff 0.2797 m Ɵ Side slop 3.67 ° mm 70.4 ؟Pm Mean precipitation of rainiest month P Mean annual precipitation 539 mm m 3000 ؟H Average catchment height C Capacity of the reservoir 162.5×106 m³ AD drainage area 1244×106 m² coefficient for Coarse sediment 1.0 K

coefficient for Medium sediment 0.1 coefficient for Fine sediment 0.046

I mean annual discharge 11.04 m³/s

Dam site

Figure1: The Location of Shahid Rajaei Dam [1]

The actual data This study has benefited from Shahid Rajaei reservoir hydrographic map which was prepared in 2008. This map was scrutinized with the help of the software which gave the actual volume and area of each elevation and also the longitudinal profile of the reservoir in order to study the manner of sedimentary delta progress towards the dam. Empirical relations In order to determine the percentage risk of sedimentation in this dam, the sediment inflow, trap coefficient and the manner of sediment distribution are studied by means of hydrological data of the catchment area and empirical relations which are explained in the next section.

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6. Examining the amount of sediment inflow into the reservoir by means of observed data The operation of depth measurement of Shahid Rajaei Dam was performed in 1998 and 2008. In 1998, according to the dam operating organization report and, the information concerning the reservoir volume in different elevations was made available. But to determine the amount of deposit sediment in this reservoir, the 2008 hydrographic maps must also be applied. These maps were examined by using civil 3D software and area-volume-elevation graph was found. Therefore, the amount of sedimentation in reservoir can be found by considering the difference in the amount of the reservoir volume in a period of 10 years. It was diagnosed that the amount of deposit sediment within 1998 till 2008 was around 2.5 million cubic meters. Operating organization has also reported the average amount of sediment inflow to the reservoir as 2.5 million cubic meters. The area-volume–elevation graph has been shown in Figure 2.

Figure 2: Volume-Area-Elevation graph of Shahid Rajaei Dam (1996 & 2008)

7- Examining appropriate empirical equations for the estimation of sedimentation in the catchment area There are many empirical relations for estimating the sediment inflow to the reservoir. Many of these relations consider the annual sediment inflow as a function of the catchment area. In this study by considering the characteristics of the region and validity assessment in reservoirs of Iran such as Latian Dam (Behrangi et al., 2008) and (behrangi et al., 2014), (Pourbojarian et al.,2009) ,Torogh Dam (Amini et al.,2009) and (Akbarzadeh et al.2010), selective empirical relations for Shahid Rajaei Dam were chosen from about 20 empirical equations presented by different sources. These relations, along with the amount of sediment inflow into Shahid Rajaei reservoir have been shown in Table 2. So far, aforementioned relations have been used for estimating the annual sediment inflow into the reservoir. It is necessary to make it clear how much of this sediment will deposit in the reservoir? To do this, empirical relations concerning sediment trap coefficient in reservoirs are used (Xiaoqing, 2003). According to the given relation, this coefficient is defined according to the relation below and is expressed by percent.

Vst Vso (1) Te 100 Vst

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In this relationV si , V so & Te in order present the total volume of inflow sediment (suspended load + bed load), the volume of outflow sediment in t period and trap coefficient. The empirical relations for determining trap coefficient are also numerous and varied. These relations have been selected on the basis of the global validity (Xiaoqing, 2003) and also their reliability in Iran’s reservoirs which were specified in the past researches (Pourbojarian et al., 2009). Table 3. Indicates these selected relations.

Table 2: The amount of annual sediment inflow into Shahid Rajaei reservoir based on presented empirical equations Equation Sediment inflow into the Reference reservoir (MCM) 0.229 Q 2 . 4 A 0.346 Strand (1975) s 0.49

Q 4s 1 3 9 R 0.200 Salas (Xiaoqing, 2003)

0.24 Strand & Pemberton Q 1.84 A 0.248 s (Xiaoqing, 2003)

1.13 Q 0 . 0 3 4Q 0.427 Galay & Evans (1989) s

0.581.23 0.13 0.227 Lal et al. (1977) Q0.774s  C / II / AR  

2 P 2 log Q2.65 log()0.46m log()1.56 H 0.609 Furineh (Xiaoqing, 2003) s PA

Table 3: The amount of Trap coefficient in Shahid Rajaei dam based on empirical equations. Trap Equation coefficient Reference (%)  1 T = 100 1 - 99.6367 Brown(1944) e C 1 + 2099.7375K AD 1.5 1 99.9999 Brune (1953) T1e  100  1 100( C / I )

C Log   Dendy (Xiaoqing, 0.19 I 95.9366 T1000.97e  2003)

0.78 8000 36 C  I  T  101.4585 Rakash & Garg(2008) e 0.78 78.85  C  I  C  I  Rakash & Garg

Te  99.99995 0.00013 0.010.0000166CC (2008)   II   graph 99 Churchill(1948)

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As we can see in Table 3, all methods have offered large quantities for trap coefficient and their maximum difference is 8%. For certainty, the trap coefficient is assumed 100%, which means all inflow sediment will deposit in the reservoir. As mentioned before, by examining the hydrographic maps, existing reports and results (Ghaderi et al.,2010), the annual average deposited sediment in reservoir is declared as 0.25 million cubic meters ; therefore, among the stated empirical relations, Strand and Pemberton and Lal et al. formulas have proved the best accuracy.

8. A survey on the manner of sediment settling in reservoir by empirical relationships There are three different shapes of longitudinal profiles of deposits in reservoirs, namely delta, wedge and narrow band. The geometric shape of reservoir deposits depends on the composition and diameter of the incoming sediment load, the amount of incoming load relative to the storage capacity the geometry and operational mode of the reservoir (Xiaoqing, 2003). A delta forms in most impounding (storage) reservoirs in which the ratio of the storage capacity, V, to the incoming annual runoff, W, is large; the pool level is frequently kept at high elevations, and the incoming sediment load is comparatively coarse. A wedge forms in gorge-type reservoirs in which V/W is small, incoming sediment is comparatively fine, and the pool level frequently fluctuates. Sediment will soon reach the dam site. A narrow band may form in some of gorge-type reservoirs in which V/W is large, the incoming sediment is comparatively fine and the pool level fluctuates frequently. This shape of deposit is caused by the large fluctuations in pool level (Xiaoqing, 2003). Several rules of thumb have been developed to differentiate between the various shapes of deposits in reservoirs. (Luo, 1977) showed the result of works by equation (2) and (3). w (2) L  s sv Delta 0.78 L 1.7 (3)  Narrow band 1 .1  L 3.98  Wedge 4.38 L 5 .2

Where V is the average storage capacity in a time interval in m3, w s is the incoming sediment load in

m3 and  s is the unit weight of deposits in ton per cubic meters. Another rule of thumb to predict shape of longitudinal profile described by Jiao, 1980 referred by (Xiaoqing, 2003). (4) v/ w2Deltas   v/ w2Wedges  According to equation (2) to (4) and data of Rajaie dam reservoir, the L factor of Luo is 1.1

andv/w2.031s  . Therefore, the shape of settling sediment is delta.

9-Investigation of longitudinal sediment distribution using hydrographic maps and Civil3D software To study sediment distribution pattern in Shaheed Rajaee Reservoir, longitudinal profiles of various branches of the dam reservoir has been tracing. As Figure (3) indicates delta hasn’t been formed after 20 years (1988-2008). Because the slope is almost constant throughout the profile and it is not possible to identify different parts of delta. However it is being expected that delta formation hasn’t occurred during the initial years, regarding the small amounts of sediments input. Hence it can be concluded that the amount of delta moving toward the dam don’t threaten the dam’s operation.

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Figure 3: Longitudinal profiles of various branch of Shaheed Rajaee Dam reservoirs for 2008.

The more accurate time of delta collision to dam can be forecasted when the delta is formed in dam’s reservoir as a consequence of sedimentation in future. In this case to determine the delta’s movement speed, the longitudinal profiles of reservoir and their different parts of delta have to be compared in two different time points. When the delta’s speed and its distance to dam are determined, it is possible to forecast the distance of delta to dam in various time.

10- Conclusion In current article, the sedimentation in Shaheed Rajaee dam reservoir was investigated and the results are as follows:  Regarding to existing information and hydrographic maps the average annual sedimentation is determined 0.25 MCM. Strand and Pemberton and Lal et al. empirical relations draw accurate conclusions for sedimentation estimation. Hence these methods are reliable enough to be used for future studies.  Regarding the low volume of sediment deposition and the size of initial reservoir, it was determined that the amounts of sedimentation cannot be regarded as a main concern for the operation and maintenance organization.  In 2008 hydrographic maps were examined by Civil3D software and reservoir’s empty volume was determined in various elevation (Figure 3). By this method the more accurate reservoir’s water storage can be determined according to water surface level.  It is possible that the sediments moving toward dam become problematic, before reservoir filled with sediments. Therefore, in this project the reservoir’s longitudinal profiles forms was investigated, using empirical relations and also hydrographic maps and Civil3D software.

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 The longitudinal profiles forms were determined using delta empirical relations. Studying hydrographic maps in 2008 (20 years after the operation of the dam) was specified that in different branches of the reservoir, the delta was not formed. Whereas progress and movement of delta toward dam occurs after delta formation, there is no concern about collision of longitudinal profiles to the dam in the near future. As mentioned earlier, the more accurate time of possible collision can be forecasted after the delta is formed in the reservoir.

11- Suggestions  To study the sedimentation phenomenon in rivers and reservoirs using numerical models or empirical relations and methods, it is necessary to have access to accurate and adequate field measurements. In addition, natural disasters such as flood or drought could change all forecasts and estimations. Hence, it is being advised to be aware and sensitive to consider and record such events.  The is a perfect example for reservoir storage of the country’s , regarding its low rate of sedimentation in reservoir and also good watershed management in upstream. It is suggested to seriously reconsider the issues of watershed management and vegetation maintenance in reservoir’s upstream lands, regarding the similarities of this dam region to other dams’.

12-Acknowledgement Sincere gratitude is hereby extended to the following who contributed to this paper without whose help it was not possible to implement this research: Dr.Ramezan Tahmasebi,Eng. Sirous Nayeri,Eng. Norouz Mohammadi,Eng. Borzoo, the personnel’s of Mazandaran Regional Water Authority and Administration of operation and maintenance of Shahid Rajaee Dam.

13- References 1. Behrangi, Farhang., Pourbojarian, Ali. And Banihashemi, Mohammadali. (2009). Comparing results of HEC- RAS model with observed values in sedimentation of Latian dam's reservoir., 8th International river engineering conference, Shahid Chamran University of Ahvaz (in Farsi). 2. Pourbojarian, Ali., Banihashemi, Mohammadali., Behrangi, Farhang and Amini, Mahdi. (2009) Sefidrood Dam Reservoir Sedimentation Estimation using GSTARS3. 8th International river engineering conference, Shahid Chamran University of Ahvaz.(in Farsi) 3. Behrangi, Farhang., Banihashemi, Mohammadali., Amiri, Leila. (2011). Latian Dam Reservoir Sedimentation Estimation using GSTARS Software and observed data, seminar on civil engineering research, Malaysia. 4. Gibson, Stanford., Brunner, Gary., Piper, Steve., and Jensen, Mark. (2006) SEDIMENT TRANSPORT COMPUTATIONS WITH HEC-RAS., PROCEEDINGS of the Eighth Federal Interagency Sedimentation Conference (8thFISC), Reno, NV, USA. 5. Behrangi, Farhang., Banihashemi, Mohammadali., Rahamanian, Mohammadreza. (2008) Study of Empirical Relations of Sedimentation in the Latian Dam Reservoir. 2nd National Conference on Dam and Hydropower (in Farsi). 6. Pourbojarian, Ali., Banihashemi, Mohammadali. and Behrangi, Farhang. (2008) Study of trapping efficiency estimation in the Sefidrood Dam Reservoir, 3th national conference on water resources, University of Tabriz,Tabriz, Iran (in Farsi). 7. Shabanloo, Mohammad., Moosavi, Farhad and Heidarpour, Mohammad. (2003) Evaluation of area reduction and area increment methods in reservoir according to time varies. 6th international congress of Civil Engineering, Esfahan(in Farsi). 8. Hasirchian, Mehraveh., Meshkati, Javad., Emadi, Ali and Taghavi, Janali. (2010) Evaluation of sediment distribution in Rajaee dam reservoir using area reduction and area increment method. 5th national congress on Civil Engineering, Mashhad(in Farsi).

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9. Pourbojarian, Ali., Behrangi, Farhang and Banihashemi, Mohammadali. (2008) How to evaluate the geometry of dam reservoirs using Civil 3D software, 14th student conference on Civil Engineering, University of Semnan, Semnan(in Farsi). 10. Behrangi, Farhang., Banihashemi, Mohammadali., Shayesteh, Mahani and Rahmanian, Mohammadreza. (2014) Sediment settling in the Latian Dam in Iran, International journal of sediment research, Vol.29 No.2 2014 pp.208-217. 11. Aminin, Mahdi., Banihashemi, Mohammadali., Pourbojarian, Ali. And Behrangi, Farhang. (2009) Study of sediment distribution in the reservoir of Torogh Dam, 8th Hydraulic conference, University of Tehran, Tehran(in Farsi). 12. Akbarzadeh, Nayereh., Majdzadeh Tabatabaei, Mohammadreza., Ghoreishi, Hossein and Behrangi, Farhang. (2010)The second national conference on integrated resource management, Shahid Bahonar University of Kerman, Kerman(in Farsi). 13. Strand, R.I., Penibertori, E. I., (1975), Reservoir Sedimentation Technical Guideline for Bureau of Reclamation 14. Galay, V.J., (1989) Sediment yield and mean annual discharge from watersheds in the Indian subcontinent. New Orleans, Louisiana. 15. Lal, V.B., et al.(1977), Siling Yield in relation to drainage basin characteristic in some Indian river valley projects, Proceedings of the Paris Symposium, IAHS-AISH. 16. Brune, G.M. (1953), Trap efficiency of reservoirs, Geophysical Union. pp. 407-418. Vol. 34. 17. Brown, C.B., (1944), Discussion of sedimentation in reservoirs. s.l. : Ed. J. Witzig. Proc. of the American Society of Civil Engineers. pp. 1493-1500. 18. Rakash, Jothip, Garg, V.,(2006) Re-look to conventional techniques for trapping efficiency estimation of a reservoir, s.l. : International Journal of Sediment Research,. pp. 76-84 . Vol. 23. 19. Churchill, M.A. (1948), Discussion of analysis and use of reservoir sedimentation data. Denver, Ed. L. C. Gottschalk, Proc. of Federal Interagency Sedimentation Conference,. pp. 139-140. 20. Xiaoqing, Y., (2003) Manual on sediment management and measurement, secretariat of the world meterological organization, WMO. 21. Tolouee, E., (1989), Reservoir Sedimentation and De-Siltation, thesis for the degree of Ph.D. Birmangam, University of Birmangam,. pp. 122–140. 22. Luo, Minsun. (1977) Reservoir Delta and its Calculation (in Chinese).

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