Peak Discharge Estimates of Glacial Lake Outburst Floods
Dr. A K Lohani Scientist F National Institute of Hydrology Roorkee
THE STUDY AREA
DEM of the study area
Creation of data base (Preprocessing of satellite data, preparing drainage, slope and elevation maps)
Slope map
NDSI image
Glacier mapping
Preparing inventory of glacial lakes (Mapping of lakes, numbering in binary tree format, finding area, locations, elevetions etc.)
Overlay analysis with glaciers
Identification of potentially dangerous lakes
Proximity analysis with other 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)
Area thresholding
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
IDENTIFICATION OF GLACIAL LAKES
Normalized Difference Water Index
(GREEN − NIR ) NDWI = (GREEN + NIR ) 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.
Table: Most vulnerable lakes detected in the basin S. Number
Lakes
Class
Lat-long
1
140
2
28
3
27
4
38
5
41
Moraine dammed Moraine dammed Moraine dammed Moraine dammed Valley
6
51
7
21
8
19
9
17
27 54’ 53.26” 88 12’ 04.89” 27 55’ 15.53” 88 09’ 51.53” 27 53’ 44.32” 88 11’ 33.33” 27 56’ 54.73” 88 18’ 30.40” 27 56’ 46.32” 88 20’ 02.47” 28 00’ 26.98” 88 29’ 50.13” 27 51’ 14.76” 88 14’ 40.23” 27 49’ 34.76” 88 15’ 22.96” 27 49’ 08.11”
Moraine dammed Moraine dammed Moraine dammed Blocked
Area (Sq. Distance from Km.) the outlet (km) 1.167
160.553
0.689
165.496
0.130
164.23
0.279
151.814
0.517
149.502
0.380
155.366
0.218
159.854
0.372
161.673
0.100
161
Table: Most vulnerable lakes detected in the basin 10
8
11
58
12
59
13
69
14
70
15
65
16
63
17
61
18
107
Moraine dammed Moraine dammed Valley Moraine dammed Moraine dammed Moraine dammed Blocked Moraine dammed Moraine dammed
27 32’ 01.48” 88 05’ 15.33” 28 00’ 59.42” 88 33’ 56.00” 28 00’ 32.65” 88 34’ 33.65” 27 58’ 26.32” 88 37’ 07.00” 27 57’ 36.55” 88 39’ 05.07” 28 01’ 35.08” 88 42’ 58.63” 28 00’ 34.95” 88 42’ 16.28” 27 59’ 34.95” 88 49’ 18.78” 27 51’ 56.13” 88 52’ 12.84”
0.264
88.054
0.201
150.304
0.198
149.905
0.559
145.051
0.163
147.719
1.044
166.982
0.805
169.569
0.157
178.056
0.150
132.789
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 Lateral shift shift 303.66 m
Change in area
66.03 m
28.66%
Lake Parameters Volume Dept Mm3 h m
4.293
37
Breach invert level m
Breach formation time
28
3.9
Breach width m
hours
76
GLOF Hydrograph at selected Site considering 50 m breach width with side slope 1:1
W72
W76
W80
GLOF Hydrograph (including 100 year flood ordinates) at selected Site considering 72, 76 and 80 m breach width with side slope 1:1
Flood peak due to glacial lake outburst Top Breach Depth Side Slope breach width
Flood at Flood at Project Lake Site Site 3/ m s m3/s
24
1.00
50
2611.14
1766.71
24
1.00
72
5237.5
2376.2
24
1.00
76
5237.5
2482.8
24
1.00
80
5237.5
2604.9
CONCLUSION