Hydrologic Cycle

Hydrologic Cycle Processes

Surface WaterSoil water

Atmospheric water

Groundwater

Processes

Precipitation

Evaporation

Surface Runoff

Groundwater Recharge

Baseflow

Map-Based Hydrology and Hydraulics

ArcViewInput Data

DEM

HEC-HMSFlood

discharge

HEC-RASWatersurfaceprofiles

ArcViewFlood

plain maps

CRWR-PrePro AvRAS

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

4 km

Watershed Delineation by Hand Digitizing

Watershed divide

Drainage direction Outlet

30 Meter MeshStandard for 1:24,000 Scale Maps

DEM Elevations

Contours

720

700

680

740

680700720740

720 720

32

16

8

64

4

128

1

2

Eight Direction Pour Point Model

DEM Elevations Contours

700

680

Austin West 30 Meter DEMElevations in meters

ftp://ftp.tnris.state.tx.us/tnris/demA.html

Flow Direction Grid

32

16

8

64

4

128

1

2

Grid Network

0 0 000

0

0

0

0

0

0

0

0

03 2 2

11 1

1 152 5

24 1

0 0 00 0

0

0

0

0

0

0

0

0

0

3 2 2

11 1

1

12

15

245

Flow Accumulation Grid

0 0 00 0

0

0

0

0

0

0

0

0

0

3 2 2

11 1

1

12

15

245

Flow Accumulation > 5 Cell Threshold

Streams with 200 cell Threshold(>18 hectares or 13.5 acres drainage area)

Watershed Draining to This Outlet

Watershed and Drainage Paths Delineated from 30m DEM

Automated method is more consistent than hand delineation

DEM Data Sources• Digital terrain models with 2’ or 4’ contours built

from aerial photogrammetry • 10m DE-DEMs, from 1:24,000 scale maps with

drainage enforcement (experimental)• 30m DEMs from 1:24,000 scale maps• 1 " seamless DEM of Texas (March, 1999)• 3" (100m) DEMs from 1:250,000 scale maps

(current state-wide coverage)• 30” (1km) DEMs global coverage

7.5´

7.5´

1º

1º

3" (100m) DEM

30m DEM

Coverage of DEMs1” seamless

DEM

Cell Size30m (1”) 100m (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

ArcViewInput Data

DEM

HEC-HMSFlood

discharge

HEC-RASWatersurfaceprofiles

ArcViewFlood

plain maps

CRWR-PrePro AvRAS

Austin Digital Elevation Model

Waller Creek

Austin Watersheds

CRWR-PrePro

ArcView-based preprocessorfor HEC-Hydrologic ModelingSystem (HEC-HMS)

Digital Elevation ModelStream Map

HMS Basin File

Control point locations

Soil and Land Use Maps

DEM Watersheds for Austin

Selected Watersheds and Streams

Mansfield Dam

ColoradoRiver

HMS Schematic Prepared with CRWR-PrePro

Mansfield Dam

ColoradoRiver

• 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 FileBasin file is a textdescription of all hydrologic elements

15533

8739Subbasin

Junction

Reach

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

ArcViewInput Data

DEM

HEC-HMSFlood

discharge

HEC-RASWatersurfaceprofiles

ArcViewFlood

plain maps

CRWR-PrePro AvRAS

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

ArcViewInput Data

DEM

HEC-HMSFlood

discharge

HEC-RASWatersurfaceprofiles

ArcViewFlood

plain maps

CRWR-PrePro AvRAS

HEC-RAS: BackgroundRiver Analysis System model of the U.S. Army Corps of

Engineers

Input = cross-section geometry and flow rates

Output = flood water elevations

Floodway Floodway

Left Bank Station

Flood Water Surface

Right Bank Station

Normal Water Surface

Main Channel

Cross-Section Schematic

Points describe channel and floodway geometry

Bank station locations

Water surface elevations and floodplain boundaries

HEC-RAS: Cross-Section Description

HEC-RAS: OutputText FileGraphical

Data translation from HEC-RAS text file to dbase table

Bank and floodplain boundaries measured from stream centerline

HEC-RAS: Data Translation

Digital orthophotograph and road coverage used as a base map

User digitizes stream with mouse

Boundary points define the RAS stream

Digital Stream Mapping

Floodplain Mapping: Plan View

3D 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

Flood hydrologyanalysis system

Nexrad radarrainfall input

Precomputedflood map

library

Real time

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