hydrological modeling. overview introduction watershed delineation automatic delineation flow length

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Hydrological Modeling

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Page 1: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

Hydrological Modeling

Page 2: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

Overview

•Introduction

•Watershed delineation

•Automatic delineation

•Flow length

Page 3: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

Introduction

Page 4: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

Watershed management

Page 5: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

Definition of watershed

• “The region draining into a river, river system, or body of water”

-American Heritage Dictionary

• The upstream area of any given point on the landscape

• Physically defined by drainage point and upstream area

• Also known as basin, sub-basin, catchment, and contributing area

Page 6: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length
Page 7: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length
Page 8: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

Watershed delineation

Page 9: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

How it works

•Water always flows downhill•For any point on a grid representing a landscape,a drop of water can be traced downhill

direction of flow is known for every DEM cell

•For any point on a grid representing a landscape,a flow pathway can be traced back uphill

flow accumulation is known for every DEM cell

•Uphill back-tracing proceeds to a ridgeline or to the edge of the grid

•Termination of uphill back-tracing defines watershed boundary

Page 10: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

Watershed delineation

Steps (with ArcToolbox):

1. Create a depressionless DEM

2. Calculate flow direction

3. Calculate flow accumulation

4. Create watershed Pour points

5. Delineate watersheds

Page 11: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

1. Creating a depressionless DEM

• DEM must eventually drain off edge of grid

• Areas of internal drainage will result in unprocessed areas

• FILL routine fills in sinks or cuts off peaks creating a new grid with no drainage errors

elevation

Page 12: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

2. Flow direction

• Every cell flows into another cell or off the grid edge

• Flow direction is calculated as the direction of steepest downward descent

• Flow direction is calculated for each cell, resulting in a new grid theme

Page 13: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

2. Flow direction

flow moves out of a cell in one of 8 directions

direction of flow is saved as a code number

Page 14: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

2. Flow direction

north-flowing cells

coded as 64

Page 15: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

2. Flow direction

Flow direction grid

Page 16: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

3. Flow accumulation

• Each cell has been coded for direction of flow

• Cumulative flow is calculated from flow direction

• Output grid is created where values are the number of upstream cells

• Lower accumulation values are ridge tops

• Higher accumulation values are valleys & stream channels

Page 17: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

3. Flow accumulation

1

3

5

Page 18: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

3. Flow accumulation

Page 19: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

single class legend

shows high flow cells

3. Flow accumulation

Page 20: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

Fit depends on accuracy of the DEM and stream layers

3. Flow accumulation

Page 21: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

4. Watershed “Pour points”

• Watersheds are defined by outlets (pour points)

• Pour points should be placed in high-flow pathways

• Basins will be generated from pour point to ridgeline or to upstream sub-basin

• Pour points should be numerically coded per sub-basin

• Pour points must be converted to a grid layer

Page 22: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

4. Watershed Pour points

•Zoom in to place pour point in center of high-flow cell

•Create as many pour points as necessary

Page 23: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

5. Delineating watersheds

•Preliminary steps are completed–Filled DEM

–Flow direction

–Flow accumulation

–Pour points created & converted to grid

•Run tool to create watersheds

Page 24: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

5. Delineating watersheds

Watersheds represent area upstream from Pour points and terminate at ridgelines, uphill sub-basin boundary, or edge of the grid

Page 25: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

5. Delineating watersheds

Page 26: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

Automatic delineation

Page 27: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

Automatic delineation

Pour points automatically selected by “intersection” of highest-flow pathways and grid edge

Page 28: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

Automatic delineation

Page 29: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

Flow length

Page 30: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

Flow length

Flow distance for every cell to outlet

Page 31: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

Flow length

Flow distance for every cell to closest stream

Page 32: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

Flow length

Euclidean distance vs. flow distance

Page 33: Hydrological Modeling. Overview Introduction Watershed delineation Automatic delineation Flow length

Homework

Read: Hydrological Modeling & Watershed Delineation, Map Layouts

Study for the exam

Presentations:

3/5 Luke, Jennifer, Josh

3/7 Chris, Prati, Carolyn