The relationship between channel width changes with confinement index and flood power of an extreme flood (Case study: Ilam Dam)

Document Type : Case Study


1 PhD Student, Faculty of Geography, University of Tehran, Iran

2 Assistant Professor, Agricultural and Natural Resources Research Center, AREEO, Zanjan, Iran

3 Professor, Faculty of Geography, University of Tehran, Iran

4 Associate Professor, Faculty of Geography, University of Tehran, Iran


Extreme floods are able to execute river geomorphological variations with a wide and substantial geological changes. Former studies of extreme floods have reported a reach of geomorphic replies from negligible change to catastrophic channel change. This article provides an evaluation of the geomorphic effects of a scarce, great value event that occurred in the Ilam Dam upstearim, on 29 October 2015. Variations in geomorphic replies among reaches are examined in the context of changes in flood power, channel competence and lateral confinement index by the use of field survey and Satellite Images (IRS). In this research which is focused on the plan of spatial units, channel width variations and calculation of peak discharges were used to estimate cross-sectional stream power and unit stream power. The analysis was performed for the widening (width ratio) at reach scale. The total data set includes 38 reaches. Because of the 2015 flood, the largest value of widening was 29 m (Reach 13) and it demonstrated a 100% change in the channel width. Flood power peak was calculated 10631 W m−2 along the rather confined reaches (Reach 31) and was much lower along the unconfined reaches. The tendency of high stream power values, and resultant high erosion rates, within the confined and partly confined reaches is a subordinate of the higher energy slope of the steeper.


Alho, P., Russell, A. J., Carrivick, J. L., & Käyhkö, J. (2005). Reconstruction of the largest Holocene jökulhlaup within Jökulsá á Fjöllum, NE Iceland. Quaternary Science Reviews, 24 (22), 2319–2334.
Andrews, E. D., & Nankervis, J. M.  (1995). Effective discharge and the design of channel maintenance flows for gravel-bed rivers. American Geophysical Union, 89, 151-164.
Barrocu, G., & Eslamian, S. (2022). Geomorphology and Flooding. In S. Eslamian & F. A. Eslamian (Eds.), Flood Handbook: Principles and Applications (pp. 23-54). CRC Press.
Baynes, E. R., Attal, M., Dugmore, A. J., Kirstein, L. A., & Whaler, K. A. (2015). Catastrophic impact of extreme flood events on the morphology and evolution of the lower Jökulsá á Fjöllum (northeast Iceland) during the Holocene. Geomorphology, 50, 422-436.
Borga, M., Stoffel, M., Marchi, L., Marra, F., & Jakob, M. (2014). Hydrogeomorphic response to extreme rainfall in headwater systems: Flash floods and debris flows. Journal of Hydrology, 518, 194-205.
Brierly, G., & Fryirs, K. J. (2005). Geomorphology and river management. Blackwell, Oxford, UK.
 Carling, P. A. (2013). Freshwater megaflood sedimentation: What can we learn about generic processes?, Earth Science Review, 125, 87-113.
Carrivick, J. L., Manville, V., Graettinger, A., & Cronin, S. J. (2010). Coupled fluid dynamics-sediment transport modelling of a Crater Lake break-out lahar: Mt. Ruapehu, New Zealand. Journal of Hydrology, 388(3-4), 399-413.
Cheetham, M. D., Bush, R. T., Keene, A., Erskine, W. D., & Fitzsimmons, K. E. (2010). Longitudinal correlation of late Quaternary terrace sequences of Widden Brook, southeastern Australia. Journal of Earth Sciences 57(1), 97-109.
Costa, J. E., & O'Connor, J. E. (1995). Geomorphically effective floods. In J. E. Costa, A. J. Miller, K. W. Potter, & P. R. Wilcock (Eds.), Natural and anthropogenic influences in fluvial geomorphology (pp. 45–56). Washington DC: American Geophysical Union.
Fewtrell, T. J., Neal, J. C., Bates, P. D., & Harrison, P. J. (2011). Geometric and structural river channel complexity and the prediction of urban inundation. Hydrological Processes.  25(20), 3173-3186.
Fuller, I. C. (2008). Geomorphic impacts of a 100-year flood: Kiwitea Stream, Manawatu catchment, New Zealand. Geomorphology 98(1-2), 84-95.
Gregory, S. V., Swanson, F. J., McKee, W. A., & Cummins, K. W. (1991). An ecosystem perspective of riparian zones. Bioscience 41(8), 540-551.
Guan, M., Wright, N. G., Sleigh, P. A., & Carrivick, J. L. (2015). Assessment of hydro-morphodynamic modelling and geomorphological impacts of a sediment-charged jökulhlaup, at Sólheimajökull, Iceland. Journal of Hydrology, 530, 336-349.
Kale, V. S., & Hire, P. S. (2004). Effectiveness of monsoon floods on the Tapi River, India: role of channel geometry and hydrologic regime. Geomorphology  57(3-4), 275-291.
Kale, V. S. (2008). A half-a-century record of annual energy expenditure and geomorphic effectiveness of the monsoon-fed Narmada River, central India. Catena 75(2), 154-163.
Khanbabaee, Z., Moghimi, E., Maghsoudi, M., Yamani, M., & Alavipanah, S. K. (2019). Investigation on the Factors Controlling the Response of Mountain Rivers to Extreme Flood Event (Case Study: Upstream Ilam Dam). Physical Geography Research  51(1), 1-15.
Kondolf, G. M., & Micheli, E. R. (1995). Evaluating stream restoration projects. Environmental Management, 19(1), 1-15.
Krapesch, G., Hauer, C., Habersack, H. (2011). Scale orientated analysis of river width changes due to extreme flood hazards. Natural Hazards and Earth System Sciences, 11(8), 2137-2147.
Kumar, S., Ranta, M., & Praveen, T. (2010). Analysis of the run off for watershed using SCS-CN method and geographic information systems. International Journal of Engineering Science and Technology, 2, 3947-3654.
Lane, S., Tayefi, V., Reid, S., Yu, D., & Hardy, R. J. (2007). Interactions between sediment delivery, channel change, climate change and flood risk in a temperate upland environment. Earth Surface Processes and Landforms, 32(3), 429-446.
Magilligan, F. J., Buraas, E., & Renshaw, C. (2015). The efficacy of stream power and flow duration on geomorphic responses to catastrophic flooding. Geomorphology 228, 175-188.
Magilligan, F. J., Phillips, J. D., James, L. A., & Gomez, B. (1998). Geomorphic and sedimentological controls on the effectiveness of an extreme flood. Journal of Geology, 106(1), 87-96.
Magilligan, F. J. (1992). Thresholds and the spatial variability of flood power during extreme floods. Geomorphology 5(3-5), 373-390.
Marchi, L., Cavalli, M., Sangati, M., & Borga, M. (2009). Hydrometeorological controls and erosive response of an extreme alpine debris flow. Hydrological Processes, 23(19), 2714-2727.
Mishra, S. K., Tyagi, J., Singh, V., & Singh, R. (2006). SCS-CN-based modeling of sediment yield. Journal of Hydrology 324(1-4), 301-322.
Moraru, A. (2017). Streambank erosion and channel widening: implications for flood hazard. Master thesis, University of Barcelona. Spain.
Phillips, J. D. (2002). Geomorphic impacts of flash flooding in a forested headwater basin. Journal of  Hydrology, 269(3-4), 236-250.
Righini, M., Surian, N., Wohl, E., Marchi, L., Comiti, F., Amponsah, W., & Borga, M. (2017). Geomorphic response to an extreme flood in two Mediterranean rivers (northeastern Sardinia, Italy): Analysis of controlling factors. Geomorphology,  290, 184-199.
Rinaldi, M., Surian, N., Comiti, F., & Bussettini, M. (2013). A method for the assessment and analysis of the hydromorphological condition of Italian streams: The Morphological Quality Index (MQI). Geomorphology 180, 96-108.
Surian, N., Mao, L., Giacomin, M., Ziliani, L. (2009). Morphological effects of different channel‐forming discharges in a gravel‐bed river. Earth Surface Processes and Landforms, 34(8), 1093-1107.
Surian, N., Righini, M., Lucía, A., Nardi, L., Amponsah, W., Benvenuti, M., Borga, M., Cavalli, M., Comiti, F., Marchi, L., Rinaldi, M., & Viero, A. (2016). Channel response to extreme floods: insights on controlling factors from six mountain rivers in northern Apennines, Italy. Geomorphology 272, 78-91.
Thompson, C., & Croke, J. (2013). Geomorphic effects, flood power, and channel competence of a catastrophic flood in confined and unconfined reaches of the upper Lockyer valley, southeast Queensland, Australia. Geomorphology 197, 156-169.
Williams, G. P., & Wolman, M. G. (1984). Downstream effects of dams on alluvial rivers. US Government Printing Office.
Wolman, M. G., & Miller, J. P. (1960). Magnitude and frequency of forces in geomorphic processes. The Journal of Geology, 68(1), 54-74.

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