Comprehensive Analysis of Hydrological and Glacial Dynamics in the Himalayas: Addressing GLOF Risks in Hydropower Development

doi:10.21203/rs.3.rs-4617124/v1

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Comprehensive Analysis of Hydrological and Glacial Dynamics in the Himalayas: Addressing GLOF Risks in Hydropower Development

https://doi.org/10.21203/rs.3.rs-4617124/v1

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In the Indian Himalayas, several hydroelectric projects are under construction or planning due to the availability of a perennial water source and a natural head for hydropower generation. However, the region faces challenges of natural disasters, particularly from the risk of glacial lake outburst floods (GLOFs) exacerbated by climate change.

The Bajoli-Holi Hydroelectric Project on River Ravi is studied to analyze its spillway capacity considering both GLOF and Inflow Design flood. Advanced methods such as hydrodynamic modeling, hydrometeorological approaches, and tools like ArcGIS for catchment delineation are employed to effectively understand and mitigate these risks. Additionally, sensitivity analysis using the MIKE 11 model helps explore various breaching parameters, enhancing the study's accuracy. This study can make the engineers and policymakers informed decisions to ensure the safety and sustainability of hydroelectric projects in the region, balancing energy generation with environmental conservation.

Breach

Design Flood

GLOF

Himalayas

Hydroelectric

River Ravi

The development of civilization across the globe is intricately linked to its per capita water availability. Dams are constructed for multipurpose needs such as irrigation, flood control, hydropower development, etc., which are essential for the development of any nation. It is crucial to conduct a sufficient inflow design flood analysis before the projects are built because increasing the spillway capacity of existing projects by providing extra spillway openings is very time-consuming and expensive and may sometimes even be non-feasible owing to its topography.

Glacial lakes usually form high altitudes above 3500 meters above the Mean sea level. Thus, the sudden rupture is more dangerous since the Kinematic velocity associated with the rupture is high enough to travel hundreds of kilometers downstream till it is dissipated and, in its path, causes extreme damage to the downstream structures across its flow path. Glacial Lake Outburst Floods (GLOFs) are a significant hazard in mountainous regions, including the Andes, European Alps, and the Himalayas. The consequences include property destruction, loss of human life due to settlement, and profound socio-economic repercussions, particularly in areas densely populated by humans.

The Glacial Lake Outburst Floods peak occurs, dissipating to normal levels once the water is completely discharged from the breach. The peak discharge resulting from a glacial lake outburst flood (GLOF) depends on a multitude of factors such as the volume of the glacial lake, characteristics of the dam (height, width, composition), potential failure mechanisms (e.g., overtopping, dam collapse, ice-dam failure), the topography downstream, and the sediment availability.

The presence of sediment downstream of a dam can lead to the formation of debris flows, typically on slopes with gradients exceeding 10 to 15 degrees. These flows are characterized by the rapid movement of sediment, posing significant hazards to surrounding areas. GLOFs not only cause immediate flooding but also transport considerable amounts of sediment, resulting in the alteration of river floodplains through erosion, transportation, and deposition processes. The alteration of the River floodplain may occur tens of kilometers away from the water source.

India is a country that depends on the Himalayas for its development since it is the only perennial source of fresh water for its northern Rivers (Jain et al. 2012). If the progress in hydropower project development is sustained, the Himalayas are expected to house the world's most significant growth rate in HPPs (Schwanghart et al. 2016). It is thus essential to analyze the safety of the structures constructed across the Rivers in the basins like the Indus, Brahmaputra, and the Ganges, located in the Himalayas, to make them hydrologically safe for their large population (Das et al. 2015; Thakur et al. 2016). Much research in India and other parts of the world is directed at the potential loss of infrastructure, biodiversity, and livelihoods from a dam failure (Allen et al. 2016). Numerous studies demonstrate a relationship between the size of glacial lakes, their fragility, and how climate change influences the increase of lake volume (Cook et al. 2013; Zhang et al. 2022). According to some research, moraine dam glacial lakes are the most susceptible to overtopping and breaching compared to other kinds of glacial lakes, which could result in sudden outflows (Mal et al. 2021). The literature review can be broadly classified into two parts. Firstly, the GLOF studies are done in many glacial lakes worldwide, specifically in the Himalayas. Secondly, the Inflow design flood and PMP estimation are associated with the hydrological design safety of the dams and related structures. Researchers agree that early detection of glacial lake hazards is a better option to mitigate its natural risks. Implementing a remediation strategy is made more accessible by using remote sensing techniques for image processing, hazard detection, monitoring, and assessment. (Richardson and Reynolds 2000). To determine where the lakes are developing and enlarging, it appears crucial to consider the gradient of the lakes and the ablation zone, and its early detection is essential (Quincey et al. 2007).

Between 1999 and 2005, in collaboration with partners across numerous nations, ICIMOD started creating an inventory of glaciers and glacial lakes and identifying potential locations for GLOF (Mool et al. 2001). Research successfully demonstrates that using GAMMA SAR processing of satellite images generates interferograms, and the result depends on orbital parameters, such as baseline length, imaging angle, surface topography, and surface displacement. (Richardson & Reynolds 2000). It is also interesting to note that not all glaciers produce glacial lakes and that longitudinal gradients are necessary for lake formation in addition to negative mass balance. (Reynolds 2000).

The geology and geography of the area impact the sort of glacial lakes generated. The lake area and volume so generated significantly affect the outburst flood, if any. So, change detection techniques using remote sensing help understand the growth or shrinkage of glacial lakes. Many empirical formulae are created to determine the depth and volume of water in such lakes based on satellite photos and validated based on many field observations. (Huggel et al. 2002; Yao et al., 2012; Allen et al. 2016; Muñoz et al. 2020). Due to the glaciated mountains' challenging topography and climatic conditions, remotely sensed data techniques help comprehend the lakes using multispectral data. (Jain et al. 2012).

Due to the rising effects of global warming and climate change, many new glacial lakes have been created and ruptured over time. Most moraine-dammed lakes were believed to have been formed at the end of the Little Ice Age (Clague and Evans 2000). The gradual recession of the glaciers from its mother glaciers also causes stable cirque and supra-glacial lakes to be formed. The expansion of such lakes proves dangerous as the storage volume of glacial melt and rainwater accumulates, forming huge catastrophic lakes with possible GLOF consequences. Cyclic outburst activity is often observed in the end moraine glacial lakes, which get ruptured and again get filled up cyclically, causing more than one failure in the same glaciated lake. It continues until the lake ruptures entirely over many years when it can no longer hold water. Research has been carried out in many areas of GLOF failures in the Himalayas, European Alps, North American Rockies, Andes, Tien Shan Mountains, and Pamirs (Reynolds 2006), and it is seen that the rising global temperature makes the lakes grow in size with time with increasing failure frequency. The GLOF magnitude is rising and will continue to increase with the current and continued global warming scenario (RGSL 2003).

The historical data indicates a notable increase in Glacial Lake Outburst Floods (GLOFs) frequency in the Himalayas. Initially, between 1940 and 1970, the region experienced approximately one major GLOF per decade. However, by the 1990s, this frequency escalated to one major outburst every three years. This rise indicates a concerning trend likely linked to climate change and the retreat of glaciers. The devastating impacts of GLOFs on human lives and infrastructure were seen in two significant events. The first occurred in December 1941 in Huaraz, located in the Cordillera Blanca region of Peru. This disaster resulted in the destruction of the city and the loss of at least 6000 lives, marking it as one of the deadliest GLOF events on record. In June 2013, the Chorabari glacial lake outburst resulted in massive loss of life and property at Kedarnath, Rambara, and Gaurikund in Rudraprayag district of Uttarakhand.

The approximate area of glaciation in the Indian Himalayas is 23,300 sq. km. (Worni et al. 2013) Glacial Hazards relate to dangers associated with glaciers and lakes in high mountainous areas and the related impacts downstream. Unstable ice-cored moraine complexes can cause catastrophic drainage. (Kumar et al. 2022), (Frey et al. 2010). Due to climate change, there is a rise in the area of the glacial lakes, and some are susceptible to bursting when dammed by unstable and non-compacted end moraine. (Westoby et al. 2014). The number of glacial lakes so formed has also increased over the years. (Zhang et al. 2022).

An Inflow Design Flood (IDF), commonly called a Design Flood, is selected to evaluate a structure's safety. It is necessary to consider various types of design floods, such as Probable Maximum Floods (PMFs), Standard Project Floods (SPFs), or floods that occur over a return period, depending on the level of security required against possible structural failures. (WMO 1994)

Dams are constructed for irrigation, flood control, the development of hydropower, and other purposes and are, therefore, essential for the development of any nation. (Lohani 2022). It is crucial to conduct a sufficient inflow design flood analysis before the projects are built because increasing the spillway capacity of existing projects by providing extra spillway openings is very time-consuming and expensive. (Pillai and Gupta 2017). If the safety aspect is overlooked, dams have huge setbacks. In the unlikely chance that they fail, the associated risk is relatively high.

The inflow design flood estimation of the Bajoli-Holi dam using the hydro-meteorological method is essential for ensuring the dam's safety. The results of this estimation will be used to develop better practices for similar projects in hydro-meteorologically similar catchments, especially in the Himalayas.

Assessing the Glacial Lake Outburst flood of the Bajoli-Holi dam will provide insight into the impact of climate change on dam safety. As glaciers continue to melt due to rising global temperatures, the risk of glacial lake outburst floods increases, and understanding this risk is crucial for ensuring dam safety. By evaluating the potential impact of glacial melt on the Bajoli-Holi dam, this study will help to guide future decision-making regarding dam safety and policies.

The Bajoli Holi hydroelectric project is a run-of-the-river scheme proposed on the Ravi River in the Chamba district of Himachal Pradesh. It is a part of the Indus Basin in India. The project's location within the Indus Basin (Fig. 1) is crucial for water resource management and energy generation. The entire project catchment is situated amidst mountainous terrain with steep hill slopes, and its location provides both opportunities and challenges. The catchment area of the proposed project lies between Longitude 76°35’15’’ E and 77°3’35’’ E and Latitude 32°10’20’’N and 32°28’7’’ N. The diversion structure is positioned at Longitude 76°40’36’’ E and Latitude 32°16’49’’N. The total catchment area of River Ravi up to the diversion site is 902 sq. km. The rain-fed catchment and the snow-fed regions are responsible for the snowline elevation at EL. 4600 is 606 km² (73%) and 296 km² (27%) respectively. The shape of the catchment area above the diversion site at Bajoli is like an elongated leaf. The River's total length from its origin to its confluence with the Indus River is nearly 720 km.

The project involves erecting a concrete gravity dam roughly 950 meters downstream from Channi Nallah, near Bajoli village. To facilitate this, the diverted water will be conveyed through a water conductor system planned along the left bank of the Ravi River. A surface powerhouse is proposed to be constructed on the left bank, close to Holi village. The dam is proposed as a concrete gravity dam with a height above the foundation at 46 meters and a length of 2420 meters. The reservoir has a Gross storage capacity of 3.7 MCM. The project forms part of the cascade development of hydroelectric projects on River Ravi, namely Kutehr, Chamera-III, and Chamera-II (Fig. 1).

Identifying potentially dangerous glacial lakes and conducting criticality analysis is crucial in assessing and mitigating risks associated with glacial lake outburst floods (GLOFs). The potentially dangerous lakes have been identified based on the water spread area and other features related to the glacial lakes. A comprehensive criticality analysis has pinpointed the most significant glacial lake within the study area. This analysis aids in prioritizing management strategies and resource allocation to mitigate the risks posed by glacial lake outburst floods (GLOFs). The lake volume of the most vital glacial lake was estimated using ICIMOD and other criteria.

The breach parameter(s) for the Glacial Lake Outburst Flood simulation were estimated using the empirical relationship developed by various researchers.

The MIKE11 model has carried out the hydrodynamic channel routing of GLOF. This involved utilizing river cross-sections derived from the ALOS Digital Elevation Model (DEM) with a horizontal resolution of 12.5 meters. These cross-sections were extracted at regular intervals of 800 meters along the river stretch, extending from the glacial lake site to the project area.

The glacial lakes inventory for the project’s catchment was prepared using LANDSAT 8 ETM+, RESOURCESAT, Sentinel multispectral data, and Google Earth Pro. The project catchment model is given in Fig. 2.

Identification of potentially dangerous lakes

There are about 83 glacial lakes in the catchment area of the Bajoli Holi HEP. About 70 glacial lakes are very small, with a surface area of less than 1 hectare. It is observed that the area of these glacial lakes varies from as low as 40 sq.m to as high as 13000 sq.m. The glacial lakes were identified and mapped in the Bajoli-Holi and are subdivided into five sub-basins, viz SB1 to SB5.

Most lakes are cirque and erosion-type lakes formed in emptying cirques eroded by ancient glaciers. Typically, larger lakes with a surface area exceeding 2 hectares are targeted for study due to their capacity to store substantial amounts of meltwater and generate more significant flood events. Five glacial lakes with a surface area (water spread area) of more than 2 hectares were identified to estimate the GLOF peak potential at the project site. Based on the criteria discussed below, the identified seven potentially dangerous glacial lakes are given in Table 1.

Table 1

List of critically potentially dangerous lakes.
Lake No.	Long (E)	Lat (N)	Elevation (m)	S.A (ha)	Riverine distance From the project site	Type of dam
GL1	77.030798	32.216437	4570	2.325	42	Erosion
GL1,2,7	77.030798	32.216437	4570	4.369	42	Erosion
GL20	76.809309	32.225735	4415	2.008	33	Moraine
GL21	76.777632	32.255783	4570	3.232	26	Moraine
GL47	76.753297	32.23354	4360	10.60	15	Moraine
GL52	76.786781	32.243935	4336	14.50	26.5	Moraine

Hydrological data for GLOF simulation

Two flood events have been selected to get a reasonable estimate of the GLOF hydrograph at the project site. The average annual flow and 100-year flood at the Bajoli Holi HEP site are given in Table 2.

Table 2

Average annual flow and 100-year flood at the Bajoli Holi project site
Project name	Catchment area (sq. km)	Average annual flow (Cumecs)	100-year flood (Cumecs)
Bajoli Holi HEP	902	52	1157

The catchment area depicting the flood impingement as a constant steady discharge at various locations is shown in Fig. 3. The area of sub-catchments and distribution of flood is given in Table 3.

Table 3

Area of sub-catchments of Bajoli basin used for flood distribution
Sub catchment no.	Area (km²)	Distribution of average annual flow (Cumecs)	Distribution of 100-year flood (Cumecs)	Impingement location (km) d/s of GL52
SB1	24	1	5	Lake
SB1	24	1	26	0.1
SB2	630	36	808	10
SB3	53	3	68	16
SB4	71	4	91	22
SB5	24	7	159	25.1
Total	902	52	1157

Distribution of lake volume for MIKE11 Model set up for GL-52.

For the GLOF simulation in MIKE11, the 2 MCM volume of the glacial lake GL52 has been distributed at different elevations, as given in Table 4.

Table 4

Cumulative volume and surface area of GL52 at different elevations
EL (m)	Surface Area (m²)	The volume between two consecutive elevations (m³)
4320	132500
4323	134844	401016
4326	137188	408048
4329	139531	415078.5
4332	141875	422109
4336	145000	573750
Total		2220002

4.1 Breach parameters for GLOF simulation for GL-52

The critical parameters associated with breaches typically include the estimated level of the breach invert, breach width, duration of breach development, and the reservoir or lake level at the time of the breach. Various empirical formulas developed by the researchers over time for the breach width and breach development time are used, and different scenarios are generated to produce the best possible estimation of the case under study.

1. Froelich 1995 B
B = 0.1803 V_w^0.32 h_b^0.19	V_w = Reservoir volume (m³) h_b = Height of water in m above breach invert level(m) B = Average breach width (m) t_f = Time of full breach development (hour)
t_f = 0.00254 V_w^o.53 h_b^−0.90
2. Federal Energy Regulatory Commission (FERC) 1987
B = 2–4 h_d	h_d = Height of water above breach invert level(m) t_f = Time of full breach development (hour)
t_f = 0.1 to 1hour

As per the Froelich equation, the average breach width is about 32.8 m, and the breach development time is about 30 minutes. As per the FERC guidelines, for a 16 m height of water above the breach invert, the average breach width varies from 32 m to 64 m. Accordingly, per FERC guidelines, the average breach width at mid-height may be assumed to be 40 m. Since the naturally formed dam is more porous than a well-compacted earthen dam hence, for a 16 m breach depth, the breach development time can be taken as 15 minutes. The breach slope may be in the 0.5 to 1H: 1V range. As many uncertainties are involved in selecting dam breach parameters, several trial/sensitivity runs have been simulated in the model by changing the breach parameters to get the most critical one. To get the most critical output through the dam breach, the following breach parameters have been adopted for the GLOF simulation, as given in Table 5.

Table 5

Final breach parameters of GL-52 adopted for the study
Breach depth	16 m
Average breach width	48 m
Breach width (bottom)	40 m
Breach width (top)	56 m
Side slope of breaching section	0.5H: 1V
Breach development time	15 minutes

Glacial Lake 52 for GLOF Simulation

From the detailed criticality analysis, the glacial lake GL52, with an estimated volume of 2.22 MCM, has been the most critical for evaluating the GLOF peak at the project site. This lake is located at a distance of about 26.4 km upstream of the project site.

MIKE 11 models set up for GLOF study of GL-52

The GLOF study comprises dam break simulation and hydrodynamic channel routing of dam break (GLOF) flood. Glacial lake GL52 is located about 26.48 km upstream of the diversion site of Bajoli Holi HEP. For the GLOF study, the 27.86 km reach of the River from the GL52 up to 1.38 km downstream of the Bajoli Holi HEP site has been represented in the MIKE-11model set up by river cross sections at an interval of approximately 400 m. The downstream boundary of the GLOF model set-up has been applied at 27.86 km, i.e. 1.38 km downstream of the diversion site. Manning's roughness coefficient for the entire study reach was 0.050, considering the boulder river beds of hilly terrain and the large debris flow associated with GLOF. The bed profile of the River in the study reach is given in Fig. 4.

The glacial lake GL52 is represented in the model by the elevation–area relationship. The moraine dam, which blocks the lake, is characterized by its crest elevation and length, with parameters specified for potential breach. A constant inflow of 2 Cumecs serves as the upstream boundary for the model configuration. The normal depth option has been selected as a downstream boundary, applied 1.38 km downstream of the diversion site. The MIKE11 model setup is given in Fig. 5.

Hydrological data for GLOF simulation for GL-52

Glacial lake outburst floods occur primarily in combination with a flood event. The River can be assumed to be in an initial condition with an average annual or 100-year return period flood flow depending on its pre-existing hydrological condition. These form the upper and lower limits while analyzing a GLOF event. The translation and attenuation of the flood peak in the presence of a GLOF event are analyzed by generating these two scenarios of flood flow in the natural River channel. The initial condition of the River is a necessary criterion for the hydrodynamic wave approach of channel routing. The channel routing of the combined GLOF and the initial condition of the River give a reasonable estimate of the flood peak and its occurrence time.

In the project, the first scenario analyzed is when the GLOF event occurs while the River is at an initial condition of average annual flow, and the second scenario is generated when the GLOF event occurs while the River is at a 100-year return period flood condition. The average annual flow and 100-year flood at the Bajoli Holi HE project site are given in Table 6.

Table 6

Initial Conditions of the River Channel
Project name	Distance from GL52 (km)	Catchment area (sq. km)	Average annual flow (Cumecs)	100-year flood (Cumecs)
Bajoli Holi HE Project	26.48	902	52	1157

The sensitivity analysis of the glacial lake was carried out by varying the breach parameters, breach width, breach slope, and the time of full breach development. Two scenarios of the river flow conditions were generated: First, when the river is at a 100-year flood flow condition and second, when the river is flowing at mean annual flow (MAF) condition of 1157 Cumecs and 52 Cumecs, respectively. The average yearly flood and 100-year flood are impinged as constant steady discharge at different locations of the River by dividing the catchment into various smaller sub-catchments, in the model set up and has been distributed based on the catchment area proportioning as per catchment area plan showing the locations of the projects and sub-catchments polygon as per Fig. 6. The area of sub-catchments and distribution of flood is given in Table 7.

Table 7

Area of sub-catchments of Ravi River used for Mean annual flow and 100-year flood distribution for GL-52
Sub catchment no.	Area (km²)	Distribution of average annual flow (Cumecs)	Distribution of 100-year flood (Cumecs)	Impingement location (km) d/s of GL52
SB1	24	1	5	Lake
SB1	24	1	26	0.1
SB2	630	36	808	10
SB3	53	3	68	16
SB4	71	4	91	22
SB5	24	7	159	25.1
Total	902	52	1157

GLOF Simulation for GL-52

The glacial lake, GL-52, located 26.4km upstream of the project site at an elevation of 4336m above MSL, has a lake area of 14.5 ha. It is the largest glacial lake in the project catchment. It has a lake depth of 16m and a lake volume of 2.2 MCM, as derived from empirical equations.

Taking the breach parameters, the GLOF simulation has been carried out on MIKE11 for the glacial lake GL-52 for the following two initial flood conditions of Ravi River:

Steady discharge corresponding to mean annual flow distributed along the study reach as per Table 7
Steady discharge corresponding to 100-year return period flood distributed along the study reach as per Table 7

GLOF Simulation results for the Initial condition of the River corresponding to MAF for GL-52

For the average annual initial discharge condition of the River, the moraine dam of GL52 has been assumed to breach 1 hour (an arbitrary time) after the start of the simulation. The maximum discharge through the breach for 16 m breach depth, 40 m bottom width, 56 m top width, and 15 minutes breach development time has been simulated as 2147 Cumecs. The GLOF hydrograph at its origin, i.e. just downstream of GL52 and at the Bajoli Holi HE Project diversion site, is given in Fig. 7.

For the average annual initial discharge condition, the GLOF peak of 2147 Cumecs at its origin gets attenuated to 571 Cumecs at the Bajoli Holi HE Project diversion site. The GLOF peak takes about 60 minutes to reach the Bajoli Holi HE Project diversion site. It may be seen that due to the very steep slope of the River, with a drop in the River bed profile from about EL 4315 m near GL52 to EL 2000 m near the project diversion site, the translation of GLOF hydrograph in the River reach is like a kinematic wave resulting very high velocity and less attenuation of flood peak.

GLOF Simulation results for the initial condition of River corresponding to 100-year return period flood for GL-52

For the initial discharge condition of the River corresponding to a 100-year flood, the moraine dam of GL52 was assumed to have been breached 1 hour after the start of the simulation. The maximum discharge through the breach for 16 m breach depth, 40 m bottom width, 56 m top width, and 15 minutes breach development time is about 2147 Cumecs. For the initial condition of the River corresponding to a 100-year flood, the GLOF hydrograph at its origin, i.e. just downstream of GL52 and at the Bajoli Holi HE Project diversion site, is given in Fig. 8.

The flood peaks along the study River reach are given in Annex-6. For the initial discharge condition of the River corresponding to a 100-year flood, the GLOF peak of 2147Cumecs at its origin gets attenuated to 952 Cumecs at the Bajoli Holi HE Project diversion site located about 26.48 km downstream of GL52. The GLOF peak takes about 37 minutes to reach the Bajoli Holi HE Project diversion site.

Glacial Lake Outburst Flood (GLOF) at Bajoli Holi HE Project for GL-52

The two simulated cases of GLOF with the Initial condition of the river with average annual flood and with a 100-year return period flood are compared in Table 8.

Table 8

Comparison of GLOF output for the simulated cases
Case No.	Initial condition of River	GLOF peak just d/s of GL52 (Cumecs)	GLOF peak at Bajoli Holi HEP (Cumecs)	Travel time of GLOF wave (minutes)
1	Average annual discharge (52 Cumecs)	2147	571	60
2	100-year return period flood (1157 Cumecs)	2147	952	37

From the above comparison, it can be concluded that due to the very steep slope of the River in the study, the translation of the GLOF hydrograph is a kinematic wave translation. The initial flood condition in the River significantly affects the attenuation of the GLOF peak. In the case of a 100-year flood initial condition, the flood peak at the project site is much higher than the average annual flow initial condition. This may be due to slight flow congestion and temporary water storage in the channel at the locations where slope transition occurs. On analysis by varying the parameters, it is observed that the most critical condition or the maximum GLOF peak at the project location is developed when the average breach width is 48m, depth-16m, breach slope 1V:0.5H and the time of full breach development is15 minutes respectively. A GLOF peak of 952 Cumecs is generated at the Bajoli-Holi HEP location. The peak observed at the glacial lake, GL-52 is 2147 Cumecs, and it takes 37 minutes for the GLOF peak to translate from the lake location to the HEP site at a distance of 26.4km. The velocity of the GLOF generated is 11.6m/s or 42km/hour. Considering the above two initial flow conditions in the River, the Glacial Lake Outburst Flood (GLOF) for the Bajoli Holi HE Project diversion site can be taken as 952 Cumecs.

In this study, the GLOF estimation is done using satellite imagery and hydro-dynamic analysis using HEC-RAS and MIKE-11 Models. The study aims to contribute to the understanding of dam safety in the context of climate change by conducting a comprehensive review of dam safety, estimating the Probable Maximum flood of the Bajoli-Holi dam along with the GLOF contribution of the largest glacial lakes in its catchment and thus ensuring that proper provisions in the Spillway discharge are allowed to accommodate the combined effect.

It utilizes some of the latest remote sensing products to monitor glacial lake growth, including Sentinel-1 SAR and Landsat 7 and 8 images. To determine the glacial lake volume, the study compared different available empirical equations and selected the most suitable for the study area. Seven out of the sixteen empirical relations given by Wang, Evans, Huggel, Cook and Quincey, Loriaux and Casassa, MRD Formula, provided similar volume estimates.

The sensitivity analysis of the GLOF study is carried out by varying the various breach parameters, and the initial condition of the river is analyzed corresponding to two conditions- the mean annual flow and 100-year flood condition, to simulate the GLOF peak attenuation and the travel time at the project site. As per the study results, a travel time of 19 minutes with a GLOF peak of 992 Cumecs and velocity of 12.5 m/s is to be expected at the project site in case of a dam breach from its most vulnerable glacial lake-47 located 15km upstream. A lake volume of 1.5 MCM and depth of 14m is analyzed using empirical equations. The lake area is about 11 hectares.

Competing interests

The authors have no relevant financial or non-financial interests to disclose.

Ethical approval

Our paper does not have negative societal impacts. No humans or animals were used in this research.

Funding

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Authors Contribution

All authors contributed to the study's conception and design. Material preparation, data collection, and analysis were performed by [Isly Issac], [N K Goel], [Wolfgang Schwanghart], and [Manohar Arora]. The first draft of the manuscript was written by [Isly Issac] and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript

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Comprehensive Analysis of Hydrological and Glacial Dynamics in the Himalayas: Addressing GLOF Risks in Hydropower Development

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1 Introduction

2 Study area

3 Materials and Methods

4 Results

4.1 Breach parameters for GLOF simulation for GL-52

5 Conclusions

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