Hydro Tools

Duality between Terrain and Drainage Network ► Flowing

water erodes landscape and carries away sediment sculpting the topography ► Topography defines drainage direction on the landscape and resultant runoff and streamflow accumulation processes

Study Area in West Austin with a USGS 30m DEM a 1:24,000 scale map Digitizing Watershedfrom Delineation by Hand

Watershed divide

Drainage direction

ArcHydro Page 57

Outlet

DEM Elevations 720

720

Contours 740 720 700 680

740 720 700

680

Hydrologic Slope - Direction of Steepest Descent 30

30

80

74

63

80

74

63

69

67

56

69

67

56

60

52

48

60

52

48

67 − 48 = 0.45 Slope: 30 2 ArcHydro Page 70

67 − 52 = 0.50 30

Eight Direction Pour Point Model 32

64

1

16 8

128

4

2

ESRI Direction encoding ArcHydro Page 69

32 64 128

Flow Direction Grid

16 8

ArcHydro Page 71

1 4

2

2

2

4

4

8

1

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4

8

4

128 1

2

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1

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16

Flow Direction Grid

32 64 128 16 8

1 4

2

Grid Network

ArcHydro Page 71

Flow Accumulation Grid. Area draining in to a grid cell 0

0 3

0 0

0

0

0

0

0

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0

0

0

0

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0

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2

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0

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0 2 11 1 2

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15 24

1

Link to Grid calculator ArcHydro Page 72

Contributing Area Grid 1

1

1

1

1

1

1

4

3

3

1

1

1

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12

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25

2

1

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1 4

1

3 12 2

1 3

1

1

3

1

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16

6 25

1 2

TauDEM convention. The area draining each grid cell including the grid cell itself.

Flow Accumulation > 5 Cell Threshold 0

0

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2

2

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Stream Network for 5 cell Threshold Drainage Area 0

0 3

0 0 0 0

0 2

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2

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0 11 1

0 2

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15

5 24

1

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

Watershed Draining to Outlet

Watershed and Drainage Paths Delineated from 30m DEM

Automated method is more consistent than hand delineation

The Pit Removal Problem

► DEM

creation results in artificial pits in the landscape ► A pit is a set of one or more cells which has no downstream cells around it ► Unless these pits are removed they become sinks and isolate portions of the watershed ► Pit removal is first thing done with

Pit Filling

Increase elevation to the pour point elevation until the pit drains to a neighbor

Carving Lower elevation of neighbor along a predefined drainage path until the pit drains to the outlet point

“Burning In” the Streams  Take a mapped stream network and a DEM  Make a grid of the streams  Raise the off-stream DEM cells by an arbitrary elevation increment  Produces "burned in" DEM streams = mapped streams

+

=

AGREE Elevation Grid Modification Methodology PLAN

GRID CELL SIZE A

A

SECTION A-A

GRID CELL SIZE

ELEVATION RESOLUTION MODIFIED ELEVATION ORIGINAL ELEVATION KNOWN STREAM LOCATION AND STREAM DELINEATED FROM MODIFIED ELEVATION STREAM DELINEATED FROM ORIGINAL ELEVATION

Stream Segments 0

0 3

0 0 0 0

0 2

0

0

2

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0

0 11 1

0 2

1 0

15

5 24

1

Stream Links in a Cell Network 1

1

1

2 3

4 4 4

ArcHydro Page 74

2

3

4 4

3 5

5

6 6 6

5 5

Stream links grid for the San Marcos subbasin

201 172 202 203 206 204

ArcHydro Page 74

209

Each link has a unique identifying number

Vectorized Streams Linked Using Grid Code to Cell Equivalents

Vector Streams Grid Streams

ArcHydro Page 75

DrainageLines are drawn through the centers of cells on the stream links. DrainagePoints are located at the centers of the outlet cells of the catchments ArcHydro Page 75

Catchments for Stream Links

Same Cell Value

Raster Zones and Vector Polygons One to one connection

DEM GridCode 3

Catchment GridID

4 5

Raster Zones Vector Polygons

Catchments ► For

every stream segment, there is a corresponding catchment ► Catchments are a tessellation of the landscape through a set of physical rules

Catchments, DrainageLines and DrainagePoints of the San Marcos basin ArcHydro Page 75

Adjoint catchment: the remaining upstream area draining to a catchment outlet. ArcHydro Page 77

Catchment, Watershed, Subwatershed. Subwatersheds Catchments

Watershed

Watershed outlet points may lie within the interior of a catchment, e.g. at a USGS stream-gaging site. ArcHydro Page 76

Summary of Key Processing Steps

► [DEM

Reconditioning] ► Pit Removal (Fill Sinks) ► Flow Direction ► Flow Accumulation ► Stream Definition ► Stream Segmentation ► Catchment Grid Delineation ► Raster to Vector Conversion (Catchment Polygon, Drainage Line, Catchment Outlet Points)

Digital Elevation Model Based Watershed and Stream Network Delineation ► Conceptual

Basis of Terrain processing for watersheds and stream networks

► Arc

Hydro tools

Arc Hydro Tools ► Created

by the ESRI Water ApFramework is Resources Applications Structure that holds tools group in Redlands, CA ► Free of charge and publicly available ► Continually being updated, so you need to get the Arc Hydro is actual tools latest version from You need two installs

ftp://RiverHydraulics:[email protected]

Terrain Preprocessing ► Start

with a DEM ► Produce a set of DEM-derived raster products ► Convert these to vector (point, line, area) features ► Add and link Arc Hydro attributes ► Compute catchment characteristics

Terrain Morphology

Help system documents each individual tool

Watershed Processing ►

Watershed and subwatershed delineation from individual points or groups of points

► Identification

and characterizati on of longest flow path in watershed

Attribute Tools

►

►

►

Properties of the watershed and stream network Accumulatio n of attributes over the network

Attach time series to features and graph them

Network Tools

► Building

the HydroNetwork (Chapter 3 in Arc Hydro book) ► Building schematic networks that link particular node points on the network

ApUtilities and Click tools

► Ap

stands for Application Framework and it’s the structure within which Arc Hydro tools operates ► You don’t have to worry about this

► Click

tools are for individual interesting things that we’ll see in Ex

Digital Elevation Model Based Watershed and Stream Network Delineation ► Conceptual

Basis of Terrain processing for watersheds and stream networks

► Arc

Hydro tools

► Application

to LIDAR and survey data in flat land with drainage structures in Southwest Florida