Modelarea Bazinelor Hidrografice in Civil 3D - Watershed Modeling

7/31/2019 Modelarea Bazinelor Hidrografice in Civil 3D - Watershed Modeling

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Unit 4 Lesson 2: Watershed Analysis Civil 3D 2010 Student Workbook 1

Watershed Analysis

OverviewIn this lesson, you learn about how Civil 3D is used to analyze surface water runoff in a

watershed. Hydrologic analysis begins with a close inspection of the terrain surface. A

watershed is the total area of land that contributes surface runoff to a particular point of

interest. A defined surface in Civil 3D may or may not entirely contain a watershed. Using the

Watershed Analysis and Water Drop tools can help determine where surface water flows on

the surface. Along with other factors such as soil type, slope, and land cover, the area of a

watershed is necessary to calculate surface runoff flow rate.

ObjectivesAfter completing this lesson, you will be able to:

Describe the different types of watersheds delineated by Civil 3D. Use watershed analysis to delineate watershed boundaries. Create surface water runoff paths.

Exercises

The following exercises are provided in a step-by-step format in this lesson:

1. Delineate Watersheds2. Visualize Runoff Paths

Lesson

2

AutoCAD Civil 3D 2010

Education Curriculum Student Workbook

Unit 4: Environmental Design


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About the Hydrologic Cycle

The hydrologic cycle is the ongoing process in which water is evaporated from oceans, lakes,

streams, and rivers and then redistributed to the surface of the earth in the form of

precipitation. When precipitation, such as rain or snow, falls on the land surface, it encounters a

number of different fates. A portion of the precipitation returns to the atmosphere as water

vapor, or evaporates. Some of this water vapor is consumed by trees and other plant matter,

and is eventually passed back to the atmosphere through their leaves in a process is called

transpiration. Some precipitation infiltrates into the earth's soil and may be stored there as

groundwater or it may continue flowing through the soil until it reaches a stream or river.

Finally, some precipitation becomes surface runoffand enters our streams, rivers, and lakes.

Civil and environmental engineers study the behavior of surface runoff to learn more about

floods, droughts, and water pollution. Humans can greatly impact surface runoff patterns by

altering the way land is used. When studying surface runoff, the basic hydrologic unit is thewatershed.

About Watersheds

A watershedis an area that contributes surface water runoff to a particular point of interest,

also called an outlet point. Any precipitation that falls within this area, and does not evaporate,

transpire, or infiltrate, will run overland and eventually pass this outlet point. Because any point

may be designated as a point of interest, the number of possible watersheds is infinite.

However, logical points are typically designated as outlet points, such as the confluence of a

tributary with a main stream or, in a developed area, where two storm sewers join.

Delineation, or outlining, of the area which drains to a particular outlet point is of particular

importance, because the volume of surface runoff is directly proportional to the drainage area.

Civil 3D automatically analyzes a surface based on the triangles of the TIN to determine the

outline of watersheds on the surface. This analysis is performed using the Analysis tab of the

Surface Properties of any surface.

There can be several different types of watersheds present on a surface based on the type of

drain target of the watershed. A drain target is the location where the water flow either stops

or leaves the surface. Water that flows along an area or across a surface triangle eventually

flows off the surface, or it reaches a point from which there is no downhill direction. For each

drain target in a surface, Civil 3D determines the region of the surface that drains to that target.

This region is called the watershed for that drain target.

The types of watersheds analyzed by Civil 3D include those listed in the following table.


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Watershed Description

Boundary Point If the downhill end of a channel edge is on the surface boundary, then water

flowing through that channel continues off the surface. The boundary point

is the lowest end of the channel.

Boundary Segment If an edge on the surface boundary belongs to a triangle that slopes down

toward that edge, then water flows off the surface all along that edge. A

boundary segment is a connected sequence of such edges.

Depression If a point is at a lower elevation than all its neighboring TIN points, then

when water flows to it, it has no downhill place to go. Similarly, a connected

set of points that are at the same elevation and all of whose neighbors are

at a higher elevation, is a single drain target. A depression is any such set of

points.

Flat Area A flat area watershed is a flat area, from which water could flow down to

more than one drain target. It also includes the parts of the surface that

drain to that flat area. A flat area is a connected set of triangles all of whose

vertices have the same elevation. Flat areas abut parts of the surface that

slope downhill.

Multi-Drain One type of ambiguous watershed is called a multi-drain or split channel

watershed.

Multi-Drain Notch A multi-drain notch watershed occurs where there is a flat edge between

two points on a surface.

The following illustration displays several boundary segment watersheds.


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These watersheds are segregated because some of the edge triangles are sloped in towards the

surface and not towards the edge. Turning on the triangles of the surfaces along with the slopearrows clarifies this in the following illustration along the border between watershed ID 22 and

24. Note that the slope arrows are drawn along the line of the slope of the face of the TIN

triangle.

About Flow Paths

A particular path that a water drop takes for surface runoff is determined by the slope of the

individual faces of the surface. Analyzing either an existing surface or a design surface for runoffflow paths is an important step in determining how to handle stormwater at the site.

In general, you click a location on the surface as the start of the travel path for a drop of water.

The algorithm traces a line parallel to the slope of the 3D face of the TIN triangle where you

clicked until the line intersects another triangle. At that point, the path is turned to parallel the


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slope of the intersected triangle. This process continues until an endpoint is reached, which can

be the edge of the surface, or a low point or depression.

The following illustration displays the original starting point for the water drop as a red X

marker, with the subsequent path as a blue polyline until it reaches the edge of the surface.

Notice the changes in slope as the path intersects the next triangle.

Key Terms

Hydrologic Cycle The ongoing process in which water is cycled through precipitation,

runoff, infiltration, evaporation, and transpiration.

Watershed A watershed is the total area of land that contributes surface runoff to a

particular point of interest.

Drain Target A drain target is the location where the water flow either stops or

leaves the surface

Runoff Water

Path

The particular path that a water drop takes for surface runoff. The path

is determined by the slope of the individual faces of the surface.


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Exercise 1: Delineate

Watersheds

In this exercise, you modify a surface style

and perform a watershed analysis in order

to delineate watersheds and visualize

drainage patterns.

At the end of this exercise, the drawing

displays as shown.

For this exercise open \I_Watersheds-

EX1.dwg (M_Watersheds-EX1.dwg).

Configure a Surface Style

1. In Toolspace, on the Settings tab,expand the Surface, Surface Styles.

Right-click Border Only. Click Copy.

2. On the Information tab, for Name, enterWatersheds.

3. On the Watersheds tab, in theWatershed Properties table, expand the

Depression Watershed property group.

Change Use Hatching to True.

4. Click Hatch Pattern. Click .5. In the Hatch Properties dialog box:

For Pattern, select AR-SAND. For Scale, select 15. Click OK.

6. Expand the Surface property group.Change the Surface Watershed Label

Style to Watershed.

7. On the Display tab, in the ComponentDisplay table, click next to the Slope

Arrows and the Watershed to turn on

display of these components. Click OK.

Perform a Watershed Analysis

8. In Toolspace, on the Prospector tab,expand the Surfaces collection. Right-

click the Existing Ground surface. Click

Surface Properties.

9. In the Surface Properties dialog box, onthe Information tab, for Surface Style,

select Watersheds.

10.On the Analysis tab: For Analysis Type, select

Watersheds.


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Select the Merge Adjacent BoundaryWatersheds check box.

Click Run Analysis .The watersheds are analyzed and listed in

the Details table.

11.Click the Watershed Type Display button.

12.Turn off the Boundary point andBoundary segment watershed types.

Click OK twice.

13.Inspect the watersheds displayed in thedrawing.

14.In Prospector, in the Existing Groundsurface, click the Watersheds collection.

Note the list of watersheds in the Item

View area.

15.Right-click a watershed in the Item Viewarea. Click Zoom To.

You can also add a table to the drawing

that lists all of the watersheds.

16.On the Annotate tab, Labels & Tablespanel, click Tables > Add Surface Legend

Table.

17.At the prompt to specify the table type,enter W for Watersheds. Press ENTER.

18.At the prompt for Behavior, enter D forDynamic. Press ENTER.

19.Click a location in the drawing whereyou want to place the upper-left corner

of the table.

20.The legend table is displayed in thedrawing.


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Extract Watershed Boundaries

You can use the watershed analysis data

to create polygons and an associated

hatch of the watersheds.

21.In the drawing, click the surface toselect it.

22.On the contextual ribbon, Surface Toolspanel, click Extract Objects.

23.In the Extract Objects from Surface - dialog box, clear all

check boxes except for Watersheds.

Click OK.

24.Press ESC.25.Click to select a watershed boundary

polyline or hatch.

26.Enter list. Press ENTER.The text window opens to display the

attributes of the object.

27.Press ESC. Press F2.28.Close the drawing. Do not save the

changes.


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Exercise 2: Visualize Runoff

Paths

In this exercise, you use the Water Drop

tool to visualize runoff paths in the

watersheds.

At the end of this exercise, the drawing

displays as shown.

For this exercise, open

\I_Watersheds-EX2.dwg (M_Watersheds-EX2.dwg).

Visualize Runoff Paths

The Water Drop tool is a good way to

visualize flow paths and to inspect a

surface for possible problems.

1. On the Analyze tab, Ground Data panel,click Water Drop.

2. In the Water Drop dialog box, set thevalues as shown. Click OK.

3. At the Select point prompt, click severallocations in the drawing in the specified

area, which is a boundary segment

watershed (blue polygon). Press ENTER

when finished.

Markers are created where you clicked,

and a polyline shows the surface water

runoff path across the surface. Boundary

segment watersheds have multiple

locations where the low point is at the

edge of the surface, meaning that water

will continue to flow off the edge, past the

known terrain information.

4. Click one of the polylines. Enter list.


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The text box displays information about

the polyline.

5. Press ESC. Press F2.6. In Prospector, expand Surfaces and the

Existing Ground surface. Click theWatersheds collection.

7. In the Item View window, right-clickwatershed ID 50. Click Zoom To.

This is a depression watershed. Note that

the numbering may be different in the

metric drawing. Zoom to a depression

watershed.

8. On the Analyze tab, Ground Data panel,click Water Drop.

9. In the Water Drop dialog box, use theprevious settings. Click OK.

10.At the Select point prompt, click severallocations in the drawing in watershed

50. Press ENTER when finished.

11.In Prospector, right-click ExistingGround. Click Edit Surface Style.

12.In the Display tab, click to make theSlope Arrows visible. Click OK.

13.Review the slope arrow directions andcompare them to the water drop

polylines.

Sometimes it is good practice to also view

the triangles.

14.In Prospector, right-click ExistingGround. Click Edit Surface Style.

15.In the Display tab, click to make theTriangles visible. Click OK.


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It is more difficult to see the watershed

outline, but clearer to see how the

direction of the water drop path and the

slope arrows are derived.

16.Repeat these steps on differentwatersheds, including a multi-drain

watershed.

17.Close the drawing. Do not save thechanges.


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Assessment

Challenge Exercise

Instructors provide a master or challenge exercise for students to do based on this lesson.

Questions

1. What is a watershed?2. Define a depression-type of watershed.3. What is a flow path, also known as runoff water path?4. What are some major factors that are related to surface runoff flow rate?Answers

1. A watershedis an area that contributes surface water runoff to a particular point of interest,also called an outlet point.

2. If a point is at a lower elevation than all its neighboring TIN points, then when water flowsto it, it has no downhill place to go. Similarly, a connected set of points that are at the same

elevation and all of whose neighbors are at a higher elevation, is a single drain target. A

depression is any such set of points.

3. A flow path is the particular path that a water drop takes for surface runoff. The path isdetermined by the slope of the individual 3D triangle faces of the surface.

4. Watershed area, land cover, slope, and soil type are all important when calculating surfacerunoff rate.

Lesson Summary

In this lesson, you learned about the concepts of watershed analysis and how to use Civil 3D to

perform basic analysis. You used the Watershed Analysis tool for an existing surface to

delineate watersheds, extracted the boundaries as closed polygons, and inserted a watershed

legend table. You used the Water Drop tool along with slope arrows and triangles to visualize

the surface water runoff patterns on a surface.

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Modelarea Bazinelor Hidrografice in Civil 3D - Watershed Modeling