Thursday, September 1, 2016
creating a street intersection list
GOTO SOURCE: THIS IS REALLY HELPFUL FOR STREETS DEPARTMENTS:
https://blogs.esri.com/esri/arcgis/2013/02/11/streetintersectionlist/
Saturday, August 18, 2012
Convert GIS Data to AUTOCAD
Department of Survey in Nepal has been providing the
topographic maps of whole Nepal in digital format. To be more exact, it
provides the contour maps of whole Nepal in Nepalese coordinate system
(modified UTM) in either 1:25000 or 1:50000 scale. If you have ARCGIS version
9.2 or 9.3 with 3d-Analyst extension, you can easily convert the digital map
from GIS format to AUTOCAD format. I shall explain the procedure of doing this
in a layman language and hope it will help a lot of us in our studies and work. Following are the step by
step procedures:
1.
Open ARCGIS map.
2.
Open ARCGIS Catalogue.
3. Drag the file from Arc Catalogue to the ARC map
window to its left side area. Drag only
the file with name starting like “Topo LN…”
4. Open the 3d analyst
Click 3d analyst
Click convert>
convert features to 3d
5. Select the contour
file
Click input feature
attribute and select "COV" form the field.
6. save the file in your desired location and click ok.
7. click the arc tool
box. "red box"
click
"index" at its bottom
type'export to
cad"
8. Select the file and
location and ok.
Open the exported file
in AUTOCAD.
You can also export other data except TOPO_LN to cad. You just don't have to convert them to 3d. Just export to cad.
If you have any
questions regarding this please mail me the query at sarveshdhakal@gmail.com
Tuesday, March 13, 2012
Coordinate system of Nepal


![]() |
Nepal coordinate projections |
Note that using UTM or Universal Transverse macater
projection gives result like the one below. The area is not preserved. You can change the aspect like the one shown
below.
![]() |
Projection using Transverse Mecator |
![]() |
Different aspects |
![]() |
Different ellipsoids suitable for different locations |
Wednesday, February 22, 2012
The Science of
Hydrology in Nepalese Hydropower Projects
Hydrology has long
been defined as the science of the movement of water. Hydrology is an important
science, especially in case of hydropower projects simply because it determines
the scale of the project. Critical analysis of hydrological variables should be
conducted prior to any proposed hydropower development. Such detailed analyses are necessary because
a small misinterpretation of data could risk millions of dollars of investment.
In other words, if a project is decided with a head of 100 meters and river
discharge of 100 cumecs instead of 95 cumecs as a certain dependable flow due
to slight difference in methodologies, we could lose a minimum of 1 million US
dollars of energy revenue per year in the Nepalese market. What then are the data
requirements that we need to take into account when making decisions? The
answer lies in critical components of the hydrologic cycle. Some of the most
important processes of this are briefly discussed below.
1. Rainfall:
Rainfall affects the
overall catchment characteristics from vegetation to channel networks to
sediment transportation. Massive loss in reservoir storage is largely due to
sediment deposition especially during monsoon in Nepalese rivers. Because rainfall
is purely a meteorological phenomenon, it depends mainly on climatic factors
like latitude, topography, wind cycle and distance from the sea. How can so
many variables then be synchronized into one single mathematical model? The
answer lies in long term, research projects in these areas that our country has
never commenced.
I would like to highlight
two basic kinds of hydrological models. The first one is based on data
interpretation and relies on mathematics, probability; reliability analysis and
statistical tools to either interpolate or extrapolate the desired result. It
is the one largely used in Nepalese context. The other one depends mainly on
hydrological processes and are developed for a specific project. Currently we
are seeing an increase in the number of Nepalese engineers that are realizing
the need for reliable data sources. Our country’s current need is to provide a
substantial theoretical basis for designing models that incorporates both of
these modeling philosophies so that better decisions can be made with limited
risk. Long term data collection of many variables as well as sensitivity
analysis for all important variables must be well understood before modeling of
such processes can be made. These long
term datasets are also vital for calibrating models as they are developed.
With respect to the
rainfall cycle in Nepal, precipitation occurs primarily during the monsoon in
which heavy rain falls which frequently result in flash floods around the
country. Prior to the monsoon season, soil moisture content and the water table
are relatively low. During this period, climatic conditions are relatively dry,
yet snow melt fed perennial rivers are recharging the water table.. During the
monsoon season, which falls from late June to late September, soil moisture
rises and flows in the rivers surge to their highest levels. Snowmelt is also
accelerated due to rain on snow conditions over the mountains. However, not all of the rain water
flows as runoff due to considerable volumes of ground water are stored which
then raises water table levels. This condition remains throughout the monsoon period.
Subsequent to the monsoon season, the river
and water table levels fall again and the processes repeat themselves.
How do we model
rainfall then? Could we do it in a macro scale or do we study separately for
different catchments? Nepalese meteorologists must play a role in answering
these important questions.
2. Snow hydrology
This field is largely
understudied and has not attracted the attention of Nepalese hydrologists. As
such, very little data exists. Large
volumes of water are stored in the snow of our extensive mountainous regions. This
snowpack serves as a balancing reservoir in our river catchments. Snow feeds
both surface runoff and ground water which in turn feeds our rivers. Snowmelt
is the primary input into rivers during our dry seasons prior to the monsoon.
During the winter monsoon, snowmelt adds flow to rivers. As a result Nepal has
experienced unexpected lowering in duration of load shedding during February
and March every year. No past data analysis can be found in connection to the snow
hydrology in context of Nepal. Department of Meteorology and Hydrology has
established quite a few snow measuring stations but, unfortunately the data are
either hard to find or not reliable.
3. Ground water hydrology
Ground water hydrology
is also in an early stage of development in Nepal. There has been little to no study
in this field. Experts seem to be little concerned with impact of ground water
fluctuations during project development and implementation. One aspect that is
often forgotten is that ground water has a high significance in project
reliability both technically are financially. When we talk about reliability of
flow in rivers, in many ways we are talking about seasonal water table
variations. For a better understanding of river hydrology, ground water
hydrology and geohydrology needs to be well understood. Ground water contour
maps need to be plotted over time to better understand groundwater flow paths
and potential runoff volumes. Geologists and hydrologists need to work together
to develop robust datasets that can help guide hydropower development decisions.
If we observe the
trend of project development in Nepal, we find out that there is less
importance given to the very inputs of design, i.e. hydrology. Rain, snowmelt
and groundwater all serve as inputs, and the magnitude, frequency and duration
of these inputs ultimately determines a project’s future. If we arrive at
conclusions insufficient information, substantial sums of money can be lost. Due to the uncertainty in many hydrologic
inputs, decision making in hydropower development is very tricky business. Past
trends show that different consultants arrive at different conclusions for the
same river inputs. Why is there a discrepancy? When we talk about flood
analysis, the results often vary significantly. We always tend to forget that
it is the magnitude of the same flood that determines around 50% of the total
project costs.
4. Evapotranspiration
Especially in case of
reservoir projects and projects with either large or very small catchments,
there is a critical need to study the net evapotranspiration (ET) of a
project’s catchment. People don’t realize that increases in evapotranspiration,
results in tangible losses in energy production. ET on the other hand, also
affects the rainfall distribution. This is one of the reasons why we need to
study this field for a hydropower project. Projects with large catchments lose
large amounts energy through ET while projects with relatively smaller
catchments may lose small energy but it affects the overall rates of return.
5. Snow sublimation
If we observe snow
peaked mountains everyday around 1 o’clock in the afternoon, we would easily
know how snow sublimation changes the water balance of a catchment. Currently,
we have no data that indicate how much water evaporates annually by this
process.
6. Snow melt
While snow melt is
especially high during monsoons, this process provides a steady input of water
to catchments by snowmelt all around the year.
7. Glacier formation
Glaciers, their
movements and parameters affecting them are important to be studied. GLOF is
one of the major challenges and having to incorporate it into a project is a
matter of great risk and challenge both for designers and developers.
8. Topography and geology
Aspects of rocks, rock
types, slopes and faces of mountains all affect the hydrology of a catchment.
River catchments of Nepal are difficult to model. There are catchments with fairly
regular rainfall patterns towards the south east near Bay of Bengal and there
are those which fall on a rain shadow region on north and west side. For
example, the Tamakoshi river catchment receives more rainfall and snowfall than
Kaligandaki catchment. If we observe snow peaked mountains over Koshi River in
Google earth, they are whiter with large glaciers reaching up to China. If the
same is observed for Kaligandaki River, the catchment acts like a large desert.
One of the other ways of how topography affects the hydrology is that mountains
with gentle slopes on the northern sides retain more snow and vegetation than
those facing south.
The challenge is to be
able to choose an optimum design among almost infinite number of choices. Ultimately
government policies, personal and project developer’s interests determine the
fate of a project more than what is known about a potential project’s runoff
characteristics. An understanding of a project’s risk helps in decision making and arriving at
conclusions. This understanding also aids the government and private developers
in their decisions as well. The risk calculation should however be backed up
with substantial practicability both in terms of theory and data.
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