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Nicaragua Overview: Hydrologic Analysis

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Nicaragua Overview: Hydrologic Analysis. By Ketan Shah. CEVE 499. Final Individual Report ... this model, and then the survey data from Nicaragua will be ... – PowerPoint PPT presentation

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Title: Nicaragua Overview: Hydrologic Analysis


1
Nicaragua Overview Hydrologic Analysis
  • By Ketan Shah
  • CEVE 499
  • Final Individual Report

2
Hydrologic and Hydraulic Analysis
  • The hydrologic model takes many different factors
    such as rainfall, soils (infiltration),
    elevation, drainage area, and watershed shape
    into account to create an outflow hydrograph
    (flow vs. time).
  • The hydraulic model uses this data and calculates
    the height to which the water will rise according
    to the geometric properties of the stream.
  • The ultimate goal of the analysis is to find the
    height of the water at the site to ensure that it
    will never reach the height of the bridge.

3
The Analysis Model
4
Data Acquisition
  • Digital Elevation Model (DEM)
  • Elevation data of land every 90 meters
  • VMAP International Vector Data
  • Infrastructure
  • Geographic information
  • Topographic Map of Site Quad
  • 150,000 scale topographic map
  • Contour interval of 20 meters
  • Also displayed roads and other structures
  • All data was bought online from www.mapmart.com

5
Nicaragua Overview
6
Nicaragua Overview
  • The coordinates of Jinotepe are 11.85 N and
    -86.20 W.
  • The site is located in the Department of Carazo.
  • The major river in the Department of Carazo is
    the Rio Grande.

7
DEM and Site Location
8
DEM and Site Location
  • The exact site (El Panama) is located about 10 km
    southwest of Jinotepe.
  • The coordinates of Jinotepe are 11.76 N and
    -86.24 W.
  • The site is located near the foot of a small
    mountain (1000 m).
  • The steep slopes of the mountainside greatly
    influence the watersheds and increase the
    response time and peak flow of watersheds on the
    mountainside.

9
What is a watershed?
  • A watershed is the entire drainage area of a
    certain stream or river.
  • Any drop of water placed in a certain rivers
    watershed will eventually flow into that river.
  • Large watersheds can be split up into smaller
    watersheds, which in turn can be split into even
    smaller watersheds.

10
Using ArcView GIS 3.2and HEC-GeoHMS 1.0
  • Using GeoHMS, elevation data can be used to
    create stream definitions and their watershed
    boundaries.
  • The following steps were taken
  • Fill Sinks
  • Flow Direction Grid
  • Flow Accumulation Grid
  • Stream Definition (stream threshold)
  • Stream Segmentation
  • Watershed Delineation
  • Watershed Polygon Processing
  • Stream Segment Processing
  • Watershed Aggregation

11
HEC-GeoHMS
12
Watersheds and Rivers
13
Watersheds and Rivers
  • As the figure shows each larger watershed (green)
    encompasses several smaller watersheds (red)
    the size and quantity of watersheds depends on
    the definition of a river.
  • In this area, all the watersheds are long, thin
    slivers of land extending radially outward from
    the peak of the mountain.

14
Why?
  • The horizontal elevation around the mountain is
    almost the same. Small changes in horizontal
    elevation define the horizontal boundaries of the
    watersheds
  • Due to the horizontal flatness, the steep
    downhill slope dominates the flow direction,
    leading to long and narrow watersheds.

15
Rio Grande Watershed
16
Rio Grande Watershed
  • The Aragon watershed is a sub-watershed of the
    Rio Grande watershed. Thus, the Aragon river is
    a tributary of the Rio Grande.
  • Narrow watersheds dominate on the steeper slope
    of the mountain, but as the terrain flattens near
    the foot of the mountain, the watersheds become
    wider. The flow of water in the lower watersheds
    is defined more by the horizontal or overland
    slope rather than the steep downhill slope.
  • The bulge at the right of the Rio Grande
    watershed is a result of the divide along the
    side of the mountain. All the water on the other
    side flows down the other side of the mountain.

17
Topographic Map and Site
18
Topographic Map and Site
  • The watershed area is only 2.81 sq. miles.
  • The site location is near the outlet of the
    watershed
  • The Aragon watershed has no tributaries, and is
    thus independent from the watersheds surrounding
    it.
  • This simplifies the model because the site is not
    affected by rainfall anywhere but in this small
    area.

19
Aragon Watershed and Slope of Site
  • Because the elevation ranges are relatively
    equal, we can assume an almost constant slope
    throughout the watershed.
  • The slope is about 176 ft/mi (in comparison,
    Houston is 1 ft/mi).
  • The slope and narrowness of the watershed cause a
    quick response time after rainfall.
  • If rain is falling over the entire span of the
    watershed, there is a large risk of high water
    levels at the site.
  • This problem is intensified by the fact that the
    site is located near the outlet of the watershed
    thus, all of the water from the watershed must
    pass through the site.

20
What is next?
  • Next, rainfall data need to be obtained for the
    watershed for the hydrologic model. HEC-HMS will
    be used to create this model, and then the survey
    data from Nicaragua will be used to create the
    hydraulic model for the final analysis of the
    peak height of the water flow.
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