Hydrology and Floodplain Analysis, Chapter 10

Hydrology and Floodplain Analysis, Chapter 10

Hydrology and Floodplain Analysis, Chapter 10.1

Introduction to GIS GIS Geographical Information System Spatial Data Data linked with geographical location Observations in GIS: Features Point, line, and area features Human Activities Population maps, census maps, land use Event Occurs in point of time, mapped over time Time series of rainfall data at point in watershed

GIS Hydrologic Adoption Accelerants Availability of worldwide geospatial data Inexpensive, powerful computer hardware Inclusion in engineering curriculums Hydrologic GIS extensions

Hydrology and Floodplain Analysis, Chapter 10.2

Raster and Vector Data Vector Points, lines, or polygons Maps a geographic feature with lines drawn between coordinate pairs Can be associated with multiple attributes Raster Rectangular array of grid cells Digital elevation models (DEMs), gridded rainfall data, satellite imagery Most hydrologic applications use combination of both e.g. vector watershed delineation, NEXRAD raster rainfall data

Right: Raster data of gridded array of rainfall totals in southern Texas! Left: Vector delineation of Brays Bayou watershed!

Map Scale and Spatial Detail Native Scale The scale and resolution at which data are collected or measured of a map Easily manipulated within a GIS system Out-of-scale analysis can skew results Small scale map Features appear small, less detail (1:1,000,000) Large scale map Features appear large, more detail (1:500)

Datum and Spheroid For cartography, Earth treated as spheroid Ellipse rotated around minor or major axis Horizontal datum Reference frame on Earth s Surface Orients lines of latitude and longitude Geocentric or Local Local Examples: 1927 North American Datum Uses the Clarke 1866 spheroid Passes through Meades Ranch, Kansas Vertical Datum Measured from mean sea level NGVD29 and NAVD88 are North American standards

Geographic and Cartesian Coordinate Systems Projection necessary to transform from geographic coordinate system to Cartesian Different projections maintain various properties from geographic system Conformal maintain angles and shapes Equal area maintain area Equidistance maintain distance True-direction maintain direction with respect to central point Universal Transverse Mercator (UTM) Conformal and equal area Earth divided into 60 UTM zones

The UTM projection of the Earth s surface, w/ central meridian through Dodge City, Kansas" Two streams shown on a digital orthophoto showing hydrographic features with mismatched datum (Black Stream, NAD27; White Stream, NAD83) "

Hydrology and Floodplain Analysis, Chapter 10.3

Parameters Direct Measures Rainfall Infiltration Evapotranspiration Hydraulic Roughness Indirect Measure Soil Type Used to estimate infiltration characteristics Land Use/Cover Used to estimate hydraulic roughness and evapotranspiration NEXRAD Radar Reflectivity Used to estimate rainfall

Hydrology and Floodplain Analysis, Chapter 10.4

Digital Terrain Model A DTM is a representation of the terrain Gridded elevations (DEM) Triangular facets (TIN) Series of points (x,y,z) Contour lines Example of a TIN"

Hydrology and Floodplain Analysis, Chapter 10.5

Watershed Delineation Watershed boundaries are delineated by using a DEM. Assume that water flows from each cell to its lowest neighbor.

Fixing Errors Problem: Existing streams do not line up with generated stream paths in flat areas." Problem: Stream paths exit known watershed not at outlet" Solution: Burn in the stream lines to the DEM with a stream vector map. " Solution: Establish a watershed boundary with a watershed vector map."

Hydrology and Floodplain Analysis, Chapter 10.6

Software Description Modules ArcGIS Desktop ERDAS IDRISI Bentley Collection of software to create, import, edit, query, map, analyze and publish. Distributed by Earth Resource Data Analysis System (ERDAS). A popular software package for teaching and research. Distributed by Clark Labs. Software dedicated to architects, engineers, constructors and owneroperators. Includes ArcView and other products that provide mapping data use and analysis. Support for remotely sensed data includes unsupervised classification, geometric correction and map production tools. An integrated GIS and image processing software solution for the analysis and display of digital spatial information. Consists of the Bentley geospatial desktop and server products. Full featured 2-D and 3-D GIS.