Hydrologic Cycle Hydrologic Cycle Processes Atmospheric water Precipitation

Hydrologic Cycle

Hydrologic Cycle Processes Atmospheric water Precipitation Evaporation Surface Runoff Soil water Surface Water Groundwater Recharge Baseflow Groundwater

Map-Based Hydrology and Hydraulics Arc. View Input Data DEM CRWR-Pre. Pro HEC-HMS Flood discharge Arc. View Flood plain maps Av. RAS HEC-RAS Water surface profiles

GIS-Based Flood Modeling • Terrain analysis using Digital Elevation Models • Flood hydrology model for the Austin region • Creating flood plain maps for Waller Creek • Real time flood emergency management

Study Region in West Austin Hog Pen Ck 4 km

Watershed Delineation by Hand Digitizing Watershed divide Drainage direction Outlet

30 Meter Mesh Standard for 1: 24, 000 Scale Maps

DEM Elevations 720 Contours 740 720 700 680

Eight Direction Pour Point Model 32 64 1 16 8 128 4 2

DEM Elevations Contours 700 680

Austin West 30 Meter DEM Elevations in meters ftp: //ftp. tnris. state. tx. us/tnris/dem. A. html

Flow Direction Grid 32 64 128 16 8 1 4 2

Grid Network

Flow Accumulation Grid 0 0 3 0 0 0 0 2 11 1 2 5 0 0 0 0 2 0 0 0 3 2 2 0 1 0 0 11 0 0 0 1 15 0 0 2 5 24 1 15 24 1

Flow Accumulation > 5 Cell Threshold 0 0 0 3 2 2 0 0 0 11 0 0 1 15 0 0 2 5 24 1

Streams with 200 cell Threshold (>18 hectares or 13. 5 acres drainage area)

Watershed Draining to This Outlet

Watershed and Drainage Paths Delineated from 30 m DEM Automated method is more consistent than hand delineation

DEM Data Sources • Digital terrain models with 2’ or 4’ contours built from aerial photogrammetry • 10 m DE-DEMs, from 1: 24, 000 scale maps with drainage enforcement (experimental) • 30 m DEMs from 1: 24, 000 scale maps • 1 " seamless DEM of Texas (March, 1999) • 3" (100 m) DEMs from 1: 250, 000 scale maps (current state-wide coverage) • 30” (1 km) DEMs global coverage

Coverage of DEMs 1” seamless DEM 3" (100 m) DEM 1º 30 m DEM 7. 5´ 1º

30 m (1”) Cell Size 100 m (3”)

GIS-Based Flood Modeling • Terrain analysis using Digital Elevation Models • Flood hydrology model for the Austin region • Creating flood plain maps for Waller Creek • Real time flood emergency management

Map-Based Hydrology and Hydraulics Arc. View Input Data DEM CRWR-Pre. Pro HEC-HMS Flood discharge Arc. View Flood plain maps Av. RAS HEC-RAS Water surface profiles

Austin Digital Elevation Model Waller Creek

Austin Watersheds

CRWR-Pre. Pro Digital Elevation Model Stream Map Arc. View-based preprocessor for HEC-Hydrologic Modeling System (HEC-HMS) Control point locations Soil and Land Use Maps HMS Basin File

DEM Watersheds for Austin

Selected Watersheds and Streams Mansfield Dam Colorado River

HMS Schematic Prepared with CRWR-Pre. Pro Mansfield Dam Colorado River

• SCS Runoff Curve Number method determines the direct runoff from storm rainfall in small watersheds. • Curve number (CN) is a function of hydrologic soil group and land use.

HMS Basin File Basin file is a text description of all hydrologic elements 155 33 Subbasin 87 Reach Junction 39

HMS Model of the Austin Region

Design Precipitation Input

Maps Served on the Web

Nexrad Rainfall for Storm of Oct 1994

HMS Results Watershed 155 Junction 44

GIS-Based Flood Modeling • Terrain analysis using Digital Elevation Models • Flood hydrology model for the Austin region • Creating flood plain maps for Waller Creek • Real time flood emergency management

Map-Based Hydrology and Hydraulics Arc. View Input Data DEM CRWR-Pre. Pro HEC-HMS Flood discharge Arc. View Flood plain maps Av. RAS HEC-RAS Water surface profiles

Waller Creek DEM

Waller Creek HMS Model

Flood Plain Mapping

Connecting HMS and RAS

Discharge at a Particular Cross-Section

Map-Based Hydrology and Hydraulics Arc. View Input Data DEM CRWR-Pre. Pro HEC-HMS Flood discharge Arc. View Flood plain maps Av. RAS HEC-RAS Water surface profiles

HEC-RAS: Background l River Analysis System model of the U. S. Army Corps of Engineers l Input = cross-section geometry and flow rates l Output = flood water elevations Cross-Section Schematic

HEC-RAS: Cross-Section Description l Points describe channel and floodway geometry l Bank station locations

HEC-RAS: Output Graphical Text File

HEC-RAS: Data Translation l Data translation from HEC-RAS text file to dbase table l Bank and floodplain boundaries measured from stream centerline

Digital Stream Mapping l Digital orthophotograph and road coverage used as a base map l User digitizes stream with mouse

Floodplain Mapping: Plan View

3 D Terrain Modeling: Ultimate Goal

GIS-Based Flood Modeling • Terrain analysis using Digital Elevation Models • Flood hydrology model for the Austin region • Creating flood plain maps for Waller Creek • Real time flood emergency management

Real-time flood emergency mapping Nexrad radar rainfall input Offline Flood hydrology analysis system Real time Precomputed flood map library