VIVEK DHAKAL
Watershed & Watershed Delineation | Calculating Catchment Area

Watershed & Watershed Delineation | Calculating Catchment Area

What is Watershed & Watershed Delineation?

A watershed is all the land & water which contributes runoff to a common point or outlet point. It is also called a catchment or drainage area. The terms catchment & watershed are found to be used interchangeably. So, the watershed area is the land area, from where all the surface runoff converges to a single point to give common discharge. Watershed delineation thus refers to creating a boundary that represents the contributing area for a particular outlet point.

Method of Watershed Delineation

Why Watershed Delineation is required?

Watershed delineation is done primarily to define the boundary of the study area or to divide the study area into subareas. Also, watershed delineation is the initial job for calculating catchment area. So, watershed delineation has major importance in watershed management, soil conservation & hydrometeorological studies.

How to delineate watershed?

Delineating watershed means you're drawing boundary lines of the catchment on a map. Traditionally, this is done manually in the topographic maps using information from contours but some digital methods are also available nowadays. Watershed delineation can be done by following different methods:
  1. Topo Map Method
  2. Google Earth Pro Method
  3. GIS Method
While dealing with the topo map method, one should have sound knowledge of contour lines & map scale. We should be able to visualize the terrain by seeing the contour lines. We should find where ridge & valley exists and also note that the flow direction is always perpendicular to the contour line. Here are few steps for watershed delineation & calculation of catchment area from topo map:
  • Mark the outlet point in the topo map
  • Starting from the outlet point, draw lines perpendicular to the contours in such a way that the line passes through the ridges
  • Following the procedure, connect all the possible extreme points whose discharge converges into the outlet & finally, end at the outlet point.
  • After demarcation of the catchment boundary in the topo map, trace the delineated area in transparent graph paper. Count the number of squares in the graph paper that the catchment has covered & keeping in mind of map scale, determine the value of the catchment area.
                    As an alternative to this graph paper method, we can use Autocad to calculate the catchment area. For this, scan the topo map catchment & import it to the Autocad environment. Fix the scale of the imported image & retrace the catchment boundary in Autocad using polylines. Now, the area of a polygon can easily be determined in Autocad.

Google earth pro method for watershed delineation is quite famous nowadays. Using Google earth pro, we can visualize our catchment in 3D & draw the catchment boundary as a polygon by eye judgment & instantly, Google earth pro shows you the area covered by polygon in the required unit.

GIS method of watershed delineation is the most accurate among all mentioned here. While using GIS for watershed delineation & determination of catchment area, we need DEM data of study area. The DEM data is then loaded in ArcGIS & different tools are available in ArcGIS in order to delineate watershed & determine the corresponding area. Here, ArcGIS automatically delineates the catchment for you once you provide correct information to it. One can download the DEM data directly from USGS Earth Explorer for free & can proceed further in ArcGIS.
Sustainable Development Goals 2016 - 2030 | SDGs in Nepal

Sustainable Development Goals 2016 - 2030 | SDGs in Nepal

Sustainable Development Goals (SDGs) are the goals set by United Nations Organization ( UNO ) in the 70th session meeting held in September 2015. The SDGs contain 17 goals, 169 indicators & 232 sub-indicators. The 17 SDGs were adopted by 193 member countries of UNO & came into effect on January 1, 2016. The 17 SDGs are:
Current Periodic Plan | 15th Five Year Plan of Nepal

Current Periodic Plan | 15th Five Year Plan of Nepal

In Nepal, a serious effort to planned development was started after the first five-year plan (1956-1961).  The national planning commission is a specialized & apex body of the Government of Nepal for the formulation of national vision, development policy, periodic plans & sectoral policies for the overall development of Nepal. Currently, the 15th plan is in action for the fiscal year 2076/77-2080/81. The approach paper of the 15th plan has been approved by the meeting of the national planning commission chaired by Prime Minister Khadga Prasad Oli on 2076/11/19. The 15th plan has the following key objectives:
Monthly Flow Estimation | Regional & Empirical Methods in Nepal

Monthly Flow Estimation | Regional & Empirical Methods in Nepal

Monthly flow estimation of a catchment is a major task for the design of an irrigation system in a required commanded area. We generally estimate runoff as annual or monthly flow, extremely low flow & flood flow. Annual or monthly flow is required for the design of irrigation water requirements whereas extreme low flow & flood flow are determined for the design of hydraulic structures & river training works. Here, in this article, we are mainly concerned with the estimation of monthly flow in the catchment area of study. When long-term flow data of the study are available, we use the frequency analysis method. In absence of such records, we can apply regional & empirical methods to calculate monthly flows.
Design Flood Estimation | Regional & Empirical Methods in Nepal

Design Flood Estimation | Regional & Empirical Methods in Nepal

Most of the hydrological designs consider extreme flood flows. Like, in the design of hydraulic structures such as dams, weirs, barrages, bridges, etc one needs maximum flood discharge as well as maximum flood levels. Thus, design flood estimation is a major task for the design of hydraulic structures & river training works. The estimation of runoff from a catchment is a very complex problem. Runoff is generally estimated in the following different forms:
Visit Nepal 2020 | Everything You Need To Know

Visit Nepal 2020 | Everything You Need To Know

Visit Nepal 2020
There are many places to visit in Nepal. Trekking in Nepal, mountain climbing, historical & religious places, natural resources, etc are the major reasons for tourists to visit Nepal. Tourism in Nepal dates back to 1949 AD after Annapurna Himal, a massif of the Himalayas in the Northern part, was opened for the public for the ascend to its summit. In 1951 AD, Nepal was made open for international trekkers. Professional tourism started in Nepal with the successful attempt to reach the world’s highest peak, Mount Everest (Sagarmatha) by Edmund Hillary and Tenzing Norgay Sherpa in 1953 AD. In 1996, His Majesty’s Government announced the year 1998 as Visit Nepal 1998 so as to set the country’s image as a special destination for visitors with a slogan “A sustainable habitat through sustainable tourism”. Thenceforth every year is celebrated to flourish tourism in Nepal. After the very first Visit Nepal Year 1998, Nepal Tourism Year 2011 was celebrated. Then, we planned to celebrate Visit Nepal Year 2020. The campaign was first reported to be held in 2018 but later put off to 2020 due to the delay in airport & road maintenance & the delay in other reconstruction works caused by the disastrous Gorkha earthquake 2015 (magnitude 7.8 Richter).

The year 2020 was being celebrated as Visit Nepal 2020 with a slogan of “Lifetime Experiences”. Visit Nepal 2020 was officially inaugurated by the president, Bidhya Devi Bhandari on January 1, 2020. The campaign was coordinated by Suraj Vaidya. The folkloric ape-like creature, Yeti, believed to be found in the Himalayan region, was chosen as a mascot of the campaign. The official logo of the Visit Nepal 2020 campaign was designed by Udhav Rimal. The government of Nepal had aimed to welcome about 20 Lakh tourists during this campaign. But Due to the covid-19 pandemic thorough out the world, Nepal's cabinet meeting held on 2076/11/18 BS (March 1, 2020) had decided officially to cancel Visit Nepal 2020 campaign. The Visit Nepal 2020 campaign was planned to revitalize Nepal's tourism industry after devasting Gorkha Earthquake 2015.