An interesting way to look at the Himalayas is to understand the flow of water (rain, winter snow and glacial melt) from the snow covered high ranges through the vast network of valleys and streams. Hydrology is the science of visualizing and studying water flow, catchment boundaries and basins and river networks. Eco systems (chapter 8) on the planet are connected to topography (chapter 4), geography (chapter 8), climate (chapter 9) and hydrology (chapter 10). We will be using data from HydroSHEDS (hydrosheds.org) which provides provides global catchment boundaries, river networks and water flow.
Contents
- Hydro Sheds
- Base Maps
- Rivers
- Basins
- GHNP
Hydro Sheds
The HydroSHEDS database offers a suite of global digital data layers in support of hydro-ecological research and applications worldwide. Its various hydrographic data products include catchment boundaries, river networks, and lakes at multiple resolutions and scales. Download below data sets for Asia:
Base Maps
Import Hydro Rivers and Hydro Basins level 3-8 in QGIS as 7 vector layers. We will be using Natural Earth rivers, shaded relief and EarthData DEM (chapter 8) as additional layers to enhance visualization. HydroRIVERS represents a vectorized line network of all global rivers that have a catchment area of at least 10 km² or an average river flow of at least 0.1 m³/sec at 15 arc-second resolution (500m). The global coverage of HydroRIVERS encompasses 8.5 million individual river reaches with an average length of 4.2 km, representing a total of 35.9 million km of rivers globally. HydroRivers has attributes like the river reach length, the distance from upstream headwaters and ocean outlet, the river order, and an estimate of long-term average discharge.
Rivers
One important attribute of HydroRivers is the Strahler order. Initial stream segments have order 1 and as they join other stream segments of equal order the Strahler order increases. We can enhance the visualization of the river network in QGIS by hiding smaller segments at larger scales and increasing the line width as per the Strahler order to reflect increase in water flow.
Choose a Rule-based Symbology for rivers showing only the ones with Strahler over above 4:
This automatically improves the visualization at larger scales showing only major rivers:
Showing all rivers of Strahler order 2 and above in white color for a smaller area on a shaded relief DEM base layer shows clear alignment of the river drainage network and the topography of a mountainous terrain:
We can also increase the width of the rivers as per increasing Strahler order. Under Symbology – Width – Choose Assistant:
Map Strahler values from 2 to 20 to Line widths of 0.1 to 1:
This shows the river width increasing downstream:
Anyone familiar with a given region can easily identify the individual rivers:
Rivers can be overlaid on different types of base maps. Here a satellite map showing terrain: rivers draining snow capped ranges and grassy ridges into lush green valleys:
Hydro rivers shown on gray-scale DEM perfectly aligned with the topography: draining high areas (white) into low valleys (dark):
Overlay a Survey 1:50K map to quickly identify the name of each stream segment: here the Tos Nal and Tichu Nal streams, tributaries of the Parvathi river.
Basins
Basins are watersheds which define the boundaries (water divides, ridgelines) from where the rivers drain the (rain, snow, glacial melt) water from.
The HydroBASINS product follows the Pfafstetter concept and provides levels 1 to 12 globally:
- Level 1 distinguishes 9 continents
- Level 2 splits each continent into up to 9 large sub-units
- Level 3 the largest river basins of each continent start to break out
- From Level 4 onwards, the breakdown follows the traditional Pfafstetter coding
HydroBASINS divides a basin into two sub-basins at every location where two river branches
meet which each have an individual upstream area of at least 100 km2.
Level 3
First let’s take a look at basins level 3 at a continental level. Use a Categorized symbology, set value as “rand(1,10)” fo classify 10 random colors and opacity as 50%:
Overlay the Natural Earth rivers to show the respective rivers in each of the level 3 basins shows the major watersheds across Asia and major rivers draining each:
Level 4
When zooming in we can use basins of higher level. Here we are looking at 1:8 million scale of the Himalayas with level 4 basins on a shaded relief basemap with Natural Earth geo-political boundaries (and optional mountain ranges). We can distinguish major basins:
- Indus basin draining Tibet, Ladakh, Hindu Kush into Pakistan
- Shyok river basin draining the Karakoram in Ladakh
- Jhelum/Chenab/Ravi/Sutlej basin draining the western Himalayas
- Yamuna/Ganges/Ghaghara/Gandaki basin draining the mid Himalayas joining the Gambal/Son in the Ganges plains
- Brahmaputra/Manes/Tista basin draining into Bangladesh
- Pamir basin draining the Pamir mountains in Tajikistan and Afghanistan
- Yarlang basin draining the Northern Himalayas in China
Level 6
Zooming in further to a 1:1 million scale, here we show level 6 basins rendered as a “Outline: Simple Line” shown on top of a shaded relief DEM base layer. We clearly see the individual watersheds of the Sutlej, Yamuna, Bagirathi, Ganges rivers in Garhwal draining (blue) the surrounding ridgelines (yellow/orange/red) that define the boundaries of each basins. The size of each watershed (rainfall, winter snow and glacial melt) correlates to the amount of waterflow in the respective rivers. The height (yellow vs orange vs red) of the surrounding ridgelines defines the amount of winter snow (snow depth) that will melt and contribute during each month of the year as the snowline recedes during summer:
Overlaying on the standard Open Streets base map clearly shows the size of the glaciers located in each basin which will contribute to the waterflow during summer.
Level 8
Let’s zoom in further to a 1:600K scale around the Manali region showing level 8 basins on a shaded DEM base map. We can identify individual watersheds for well known rivers:
Basin Maps
Let’s now focus on creating beautiful topographic maps of individual basins.
Great Himalayan National Park
Let’s start with GHNP (Great Himalayan National Park) defined by the Tirthan and Sainj rivers. Select the HydroBasins level 8 layer in QGIS and use the Select Features tool from the toolbar to select the basin corresponding to Tirthan and Sainj rivers located Southeast from the Beas river valley:
Right click on the Basins level 8 layer and choose Export – Save Select Features As – save this basin as GHNP (ESRI Shapefile format):
A new layer is created showing the GHNP Basin.
Let’s hide everything else by changing the Symbology to Inverted Polygons with a white color fill:
The resolution of the global DEM from EarthData (chapter 8) is 30sec or 1km which is too coarse for this scale. Let’s download high resolution DEM for GHNP at 1sec (30m) using the QGIS SRTM Downloader plugin (chapter 4). The DEM raster is by default displayed in gray-scale:
Change the Symbology to Singleband Pseudocolor with Turbo color ramp to get a better visualization. Further manually adding the names of the main rivers results in a beautiful topographic map of the GHNP basin
