Peak Discharge Estimates of Glacial Lake Outburst Floods

Dr. A K LohaniScientist FNational Institute of HydrologyRoorkee

THE STUDY AREA

DEM of the study area

Glacier mapping

Preparing inventory of glacial lakes

(Mapping of lakes, numbering in binary tree format, finding area, locations, elevetions etc.)

Identification of potentially dangerous lakes

Selecting most dangerous lake for final modeling(The potentially dangerous lakes are further assessed on the

basis of distance from outlet, volume, growth etc)

Finding GLOF simulation parameters for most dangerous lakes(Cross sections from lakes to outlet, several dam geometry parameters,

volume, dam break parameters, hydrological parameters)

MIKE-11 simulation of GLOF(Making the model and running it using extracted

parameters and collect the final result)

NDSI image

Overlay analysis with

glaciers

Proximity analysis with other lakes,

Area thresholding

Slope mapCreation of data base

(Preprocessing of satellite data, preparing drainage, slope and elevation maps)

MAPPING CLEAN-ICE GLACIERS

Clean-ice glaciers can be mapped automatically using

multispectral images using NDSI approach.

NDSI uses the high and low reflectance of snow in visible

(Green) and shortwave infrared (SWIR) region respectively

and it can also delineate and map the snow in mountain

shadows. The equation is given below:

NDSI = Visible band – SWIR band / visible band + SWIR band

Glaciers in the study area

)2()NIRGREEN()NIRGREEN(NDWI

GREEN is a band that encompasses reflected green light and NIR represents reflected near-infrared radiation

The selection of these wavelengths was done to : (1) maximize the typical reflectance of water features by using

green light wavelengths(2) minimize the low reflectance of NIR by water features; and (3) take advantage of the high reflectance of NIR by terrestrial

vegetation and soil features.

Normalized Difference Water Index

IDENTIFICATION OF GLACIAL LAKES

S. Number Lakes Class Lat-long Area (Sq. Km.)

Distance from the outlet (km)

1 140 Moraine dammed

27 54’ 53.26”88 12’ 04.89”

1.167 160.553

2 28 Moraine dammed

27 55’ 15.53”88 09’ 51.53”

0.689 165.496

3 27 Moraine dammed

27 53’ 44.32”88 11’ 33.33”

0.130 164.23

4 38 Moraine dammed

27 56’ 54.73”88 18’ 30.40”

0.279 151.814

5 41 Valley 27 56’ 46.32”88 20’ 02.47”

0.517 149.502

6 51 Moraine dammed

28 00’ 26.98”88 29’ 50.13”

0.380 155.366

7 21 Moraine dammed

27 51’ 14.76”88 14’ 40.23”

0.218 159.854

8 19 Moraine dammed

27 49’ 34.76”88 15’ 22.96”

0.372 161.673

9 17 Blocked 27 49’ 08.11”88 15’ 22.96”

0.100 161

Table: Most vulnerable lakes detected in the basin

10 8 Moraine dammed

27 32’ 01.48”88 05’ 15.33”

0.264 88.054

11 58 Moraine dammed

28 00’ 59.42”88 33’ 56.00”

0.201 150.304

12 59 Valley 28 00’ 32.65”88 34’ 33.65”

0.198 149.905

13 69 Moraine dammed

27 58’ 26.32”88 37’ 07.00”

0.559 145.051

14 70 Moraine dammed

27 57’ 36.55”88 39’ 05.07”

0.163 147.719

15 65 Moraine dammed

28 01’ 35.08”88 42’ 58.63”

1.044 166.982

16 63 Blocked 28 00’ 34.95”88 42’ 16.28”

0.805 169.569

17 61 Moraine dammed

27 59’ 34.95”88 49’ 18.78”

0.157 178.056

18 107 Moraine dammed

27 51’ 56.13”88 52’ 12.84”

0.150 132.789

Table: Most vulnerable lakes detected in the basin

Fig. : Area of the lake

Fig. : Graph showing distance from the outlet of various lakes

Fig. : Graph showing percantage change in area since 2009

Lake-140

Change in area

28.66%

Lake 140 Extent changes

Longitudinal

shift

Lateral shift Change in

area

303.66 m 66.03 m 28.66%

Lake Parameters

VolumeMm3

Depthm

Breach invert level

m

Breach formation

timehours

Breachwidth

m

4.293 37 28 3.9 76

GLOF Hydrograph at selected Site considering 50 m breach width with side slope 1:1

GLOF Hydrograph (including 100 year flood ordinates) at selected Site considering 72, 76 and 80 m breach width

with side slope 1:1

W72 W76

W80

Flood peak due to glacial lake outburst

Breach Depth Side SlopeTop

breach width

Flood at Lake Site

m3/s

Flood at Project

Sitem3/s

24 1.00 50 2611.14 1766.7124 1.00 72 5237.5 2376.224 1.00 76 5237.5 2482.824 1.00 80 5237.5 2604.9

CONCLUSION