Drawdown reservoir flushing - Revision history

Bendikhansen: Text replacement - "category:Measures" to "category:Solutions"

2020-10-26T10:03:04Z

Text replacement - "category:Measures" to "category:Solutions"

Bendikhansen at 18:29, 30 September 2020

2020-09-30T18:29:52Z

Bendikhansen at 18:29, 30 September 2020

2020-09-30T18:29:00Z

Bendikhansen: /* During implementation */

2020-09-30T18:27:46Z

During implementation

Bendikhansen: /* During implementation */

2020-09-30T18:27:36Z

During implementation

Bendikhansen: /* During implementation */

2020-09-30T18:27:22Z

During implementation

Bendikhansen: /* During implementation */

2020-09-30T18:27:12Z

During implementation

Bendikhansen: /* During implementation */

2020-09-30T18:26:13Z

During implementation

Bendikhansen: /* During planning */

2020-09-30T18:24:17Z

During planning

Robert Boes: /* Introduction */

2020-04-29T08:44:55Z

Introduction

← Older revision		Revision as of 10:03, 26 October 2020
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	*Sumi, T. 2008. Evaluation of efficiency of reservoir sediment flushing in Kurobe River, ICSE, in 4th International Conference on Scour and Erosion, pp. 608–613, Tokyo, Japan.		*Sumi, T. 2008. Evaluation of efficiency of reservoir sediment flushing in Kurobe River, ICSE, in 4th International Conference on Scour and Erosion, pp. 608–613, Tokyo, Japan.

−	[[category:Sediment measures]][[category:~~Measures~~]]	+	[[category:Sediment measures]][[category:Solutions]]

@@ Line 19: / Line 19: @@
 From an ecological point of view, the capacity of the downstream river to transport the flushed sediments further downstream, as well as the potential change in water quality during the flushing need to be considered. If the shear stress is not sufficient to mobilize sediments, the flushed sediments can deposit downstream and clog in interstices. It will be even more difficult to transport the sediments later, since the shear stress threshold allowing mobilization of clogged sediments will be higher. In addition, water turbidity can be significantly modified if large concentrations of sediments are released in rivers with low to moderate discharge. To avoid large changes in water quality and deposition of sediments in the river stretch located nearby the dam, the timing of the flushing should correspond to periods of high flows. In this context, the planning of flushing operation is of very high importance to avoid impacts on the ecosystem.
-There is a large number of numerical models that can be applied to simulate the reservoir during the planning phase of flushing. Examples are HEC-RAS, ISIS, SSIIM (see Chapter 9.1 for references). Sediment management strategies including different flushing scenarios can be modelled and tested. The efficiency of the measure and it's the impact on storage capacity reduction, as well as sediment transport in the downstream river can be simulated to design the flushing operation.
+There is a large number of numerical models that can be applied to simulate the reservoir during the planning phase of flushing. Examples are [[HEC-RAS]], ISIS, [[Sediment simulation in intakes with Multiblock option (SSIIM)|SSIIM]]. Sediment management strategies including different flushing scenarios can be modelled and tested. The efficiency of the measure and it's the impact on storage capacity reduction, as well as sediment transport in the downstream river can be simulated to design the flushing operation.
 ==During implementation==
 During flushing, the discharge through the reservoir should be large enough to ensure mobilization of the deposited sediments. Low levels gate at the dam will be opened during the flushing.
-Concentration of suspended sediments and turbidity levels in the river must be monitored during flushing operations to ensure that their value remain under ecosystems thresholds and that the operation do not have significant impacts on the physical and chemical environment.Discharge and water velocity can be registered with devices such as mechanical current meter, Acoustic Doppler Velocimeter Probe (ADV), Acoustic Doppler Current Profiler Probe (ADCP).Sediment concentration in the downstream river can be monitored under flushing using acoustic sampling, optical sampling, or trap samplers.
+Concentration of suspended sediments and turbidity levels in the river must be monitored during flushing operations to ensure that their value remain under ecosystems thresholds and that the operation do not have significant impacts on the physical and chemical environment. Discharge and water velocity can be registered with devices such as [[Current meter|mechanical current meter]], [[Acoustic Doppler velocimetry (ADV)|Acoustic Doppler Velocimeter Probe (ADV)]], [[Acoustic Doppler current profiler (ADCP)|Acoustic Doppler Current Profiler Probe (ADCP)]].Sediment concentration in the downstream river can be monitored under flushing using acoustic sampling, optical sampling, or trap samplers.
 ==During operation==
@@ Line 44: / Line 44: @@
 *Tigrek, S., and Aras, T. 2011. Reservoir Sediment Management, CRC Press, Leiden, The Netherlands, 203p.
 *Sumi, T. 2008. Evaluation of efficiency of reservoir sediment flushing in Kurobe River, ICSE, in 4th International Conference on Scour and Erosion, pp. 608–613, Tokyo, Japan.
 [[category:Sediment measures]][[category:Measures]]

@@ Line 19: / Line 19: @@
 From an ecological point of view, the capacity of the downstream river to transport the flushed sediments further downstream, as well as the potential change in water quality during the flushing need to be considered. If the shear stress is not sufficient to mobilize sediments, the flushed sediments can deposit downstream and clog in interstices. It will be even more difficult to transport the sediments later, since the shear stress threshold allowing mobilization of clogged sediments will be higher. In addition, water turbidity can be significantly modified if large concentrations of sediments are released in rivers with low to moderate discharge. To avoid large changes in water quality and deposition of sediments in the river stretch located nearby the dam, the timing of the flushing should correspond to periods of high flows. In this context, the planning of flushing operation is of very high importance to avoid impacts on the ecosystem.
-There is a large number of numerical models that can be applied to simulate the reservoir during the planning phase of flushing. Examples are [[HEC-RAS]], ISIS, [[Sediment simulation in intakes with Multiblock option (SSIIM)|SSIIM]]. Sediment management strategies including different flushing scenarios can be modelled and tested. The efficiency of the measure and it's the impact on storage capacity reduction, as well as sediment transport in the downstream river can be simulated to design the flushing operation.
+There is a large number of numerical models that can be applied to simulate the reservoir during the planning phase of flushing. Examples are HEC-RAS, ISIS, SSIIM (see Chapter 9.1 for references). Sediment management strategies including different flushing scenarios can be modelled and tested. The efficiency of the measure and it's the impact on storage capacity reduction, as well as sediment transport in the downstream river can be simulated to design the flushing operation.
 ==During implementation==
 During flushing, the discharge through the reservoir should be large enough to ensure mobilization of the deposited sediments. Low levels gate at the dam will be opened during the flushing.
-Concentration of suspended sediments and turbidity levels in the river must be monitored during flushing operations to ensure that their value remain under ecosystems thresholds and that the operation do not have significant impacts on the physical and chemical environment. Discharge and water velocity can be registered with devices such as [[Current meter|mechanical current meter]], [[Acoustic Doppler velocimetry (ADV)|Acoustic Doppler Velocimeter Probe (ADV)]], [[Acoustic Doppler current profiler (ADCP)|Acoustic Doppler Current Profiler Probe (ADCP)]].Sediment concentration in the downstream river can be monitored under flushing using acoustic sampling, optical sampling, or trap samplers.
+Concentration of suspended sediments and turbidity levels in the river must be monitored during flushing operations to ensure that their value remain under ecosystems thresholds and that the operation do not have significant impacts on the physical and chemical environment.Discharge and water velocity can be registered with devices such as mechanical current meter, Acoustic Doppler Velocimeter Probe (ADV), Acoustic Doppler Current Profiler Probe (ADCP).Sediment concentration in the downstream river can be monitored under flushing using acoustic sampling, optical sampling, or trap samplers.
 ==During operation==
@@ Line 40: / Line 40: @@
 =Relevant literature=
+*Kondolf G.M., Gao Y., Annandale G.W., Morris G.L., Jiang E., Zhang J., Cao Y., Carling U.P., Fu K.,  Guo Q., Hotchkiss R., Peteuil C. , Sumi T., Wang H.‐W.,  Wang Z., Wei Z., Wu B., Wu C. and Yang C. T. 2014. Sustainable sediment management in reservoirs and regulated rivers: experiences from five continents. Earth's Future, 2 (2014), pp. 256-280
 [[category:Sediment measures]][[category:Measures]]

@@ Line 24: / Line 24: @@
 During flushing, the discharge through the reservoir should be large enough to ensure mobilization of the deposited sediments. Low levels gate at the dam will be opened during the flushing.
-Concentration of suspended sediments and turbidity levels in the river must be monitored during flushing operations to ensure that their value remain under ecosystems thresholds and that the operation do not have significant impacts on the physical and chemical environment. Discharge and water velocity can be registered with devices such as [[Current meter|[mechanical current meter]], [[Acoustic Doppler velocimetry (ADV)|Acoustic Doppler Velocimeter Probe (ADV)]], [[Acoustic Doppler current profiler (ADCP)|Acoustic Doppler Current Profiler Probe (ADCP)]].Sediment concentration in the downstream river can be monitored under flushing using acoustic sampling, optical sampling, or trap samplers.
+Concentration of suspended sediments and turbidity levels in the river must be monitored during flushing operations to ensure that their value remain under ecosystems thresholds and that the operation do not have significant impacts on the physical and chemical environment. Discharge and water velocity can be registered with devices such as [[Current meter|mechanical current meter]], [[Acoustic Doppler velocimetry (ADV)|Acoustic Doppler Velocimeter Probe (ADV)]], [[Acoustic Doppler current profiler (ADCP)|Acoustic Doppler Current Profiler Probe (ADCP)]].Sediment concentration in the downstream river can be monitored under flushing using acoustic sampling, optical sampling, or trap samplers.
 ==During operation==

@@ Line 24: / Line 24: @@
 During flushing, the discharge through the reservoir should be large enough to ensure mobilization of the deposited sediments. Low levels gate at the dam will be opened during the flushing.
-Concentration of suspended sediments and turbidity levels in the river must be monitored during flushing operations to ensure that their value remain under ecosystems thresholds and that the operation do not have significant impacts on the physical and chemical environment. Discharge and water velocity can be registered with devices such as [Current meter|[mechanical current meter]], [[Acoustic Doppler velocimetry (ADV)|Acoustic Doppler Velocimeter Probe (ADV)]], [[Acoustic Doppler current profiler (ADCP)|Acoustic Doppler Current Profiler Probe (ADCP)]].Sediment concentration in the downstream river can be monitored under flushing using acoustic sampling, optical sampling, or trap samplers.
+Concentration of suspended sediments and turbidity levels in the river must be monitored during flushing operations to ensure that their value remain under ecosystems thresholds and that the operation do not have significant impacts on the physical and chemical environment. Discharge and water velocity can be registered with devices such as [[Current meter|[mechanical current meter]], [[Acoustic Doppler velocimetry (ADV)|Acoustic Doppler Velocimeter Probe (ADV)]], [[Acoustic Doppler current profiler (ADCP)|Acoustic Doppler Current Profiler Probe (ADCP)]].Sediment concentration in the downstream river can be monitored under flushing using acoustic sampling, optical sampling, or trap samplers.
 ==During operation==

@@ Line 4: / Line 4: @@
 [[file:sediment_drawdown_switzerland.png|thumb|250px|Figure 2: River Aare in Haslital (CH) with highly increased suspended load after the flushing at reservoir Räterichsbodensee.]]
-Dams act as a barrier for sediment transport in river systems. Sediments-laden inflows bring sediments from upstream catchment that will be trapped when reaching the reservoir. Sediments deposit in the bottom of the reservoir and reduce its storage capacity. In geographical areas with very high sediment yields, reservoirs can be filled with sediments after some years of operation, and the reservoirs not fulfill their water storage function anymore.
+Dams act as a barrier for sediment transport in river systems. Sediments-laden inflows transport sediments from upstream catchment that will be trapped when reaching the reservoir. Sediments deposit in the bottom of the reservoir and reduce its storage capacity. In geographical areas with very high sediment yields, reservoirs can be filled with sediments after some years of operation, and the reservoirs not fulfill their water storage function anymore.
-Reservoir flushing consists in removing deposited sediments out of the reservoir to retrieve the reservoir storage capacity. As a result of flushing, deposited sediments will be mobilised and released downstream the dam inducing a supply of sediments in the downstream river at the time of operation. Reservoir flushing is mainly a reservoir management measure. However, the supply of sediments induced by flushing could help to re-balance the deficit in the downstream river if the timing of the operation and the amount of sediments flushed match the transport capacity of the river (Morris et al. 1998, Tigrek et al. 2011, Kondolf et al. 2014).
+Reservoir flushing consists in removing deposited sediments out of the reservoir to retrieve the reservoir storage capacity. As a result of flushing, deposited sediments will be remobilised and released downstream of the dam inducing a supply of sediments in the downstream river at the time of operation. Reservoir flushing is mainly a reservoir management measure. However, the supply of sediments induced by flushing could help to re-balance the deficit in the downstream river if the timing of the operation and the amount of sediments flushed match the transport capacity of the river (Morris et al. 1998, Tigrek et al. 2011, Kondolf et al. 2014).
-Reservoir flushing necessities a complete emptying of the reservoir when planned outside flood periods, thus interferes with hydropower operations. The reservoir is drawn down to establish flow conditions through the reservoir that are similar to river flow conditions. Low-level gates at the dam are opened to let water flows out of the reservoir. The free water surface should be at or lower than the gate level. However, in large rivers with runoff-rivers hydropower plants, sediment flushing does not necessarily require a complete stop of power production
+Reservoir flushing necessitates a complete emptying of the reservoir when planned outside of flood periods, thus interfering with hydropower operations. The reservoir is drawn down to establish flow conditions through the reservoir that are similar to the river flow conditions prior to dam construction. Low-level outlet gates at the dam are opened to release water flows out of the reservoir. The free water surface should be at or lower than the gate level. However, in large rivers with run-of-the-river hydropower plants, sediment flushing does not necessarily require a complete stop of power production.
 =[[Methods, tools, and devices]]=