How does the length of arrow in drainage catchment affects time of overland flow

Create Length in Catchment #

Go to:

1. Open Project >> Drain
2. Click Catchment tab (Image 1)

Image 1

3. Create Catchment (Image 2)

Image 2

Overland flow time #

1. Catchment >> Spread Input >> Define drain (image 3) >> Overland Flow >>Time (min) >> Click on three dots >> Overland Flow Time box (image 4)

Image 3

Image 4

The length (L) is calculated as per image above is 20.058 m.

2. Click Apply

Result of overland flow time is shown as in Image 5.

Image 5

The overland time stated above is 14.174 min.

Overland Time affected when Arrow Length Changed #

Go to:

1. Click the arrow, then click again to move the arrow point (Image 6)

Image 6

Overland flow time #

1. Catchment >> Spread Input >> Overland Flow >>Time (min) >> Click on three dots >> Overland Flow Time box (Image 7)

Image 7

As can be seen, the length (L) has changed to 39.558 m.

2. Click Apply

Result of overland flow time is shown as in Image 8

Image 8

The overland time stated above has changed to 16.710 min as the arrow length has changed. As can be seen, overland time is affected by the arrow length in catchment.

This also can be manually calculated as image below. The spreadsheet of the calculation is appended at the end of this article.

Software Calculation (refer to Section 1.0) #

Length is the measurement of the arrow length which indicating the length between the catchment to drain. The measuring in the software can be proven by using:

1. AutoCAD

Measure the arrow length in ACAD

Image 9 Measurement measured in ACAD

Image 9 shows 20058.377 mm which tally with the software (refer image 4, (L) 20.058 m)

1. MiTS Software

Go to :

CAD >> Measure (specify first point to second point)

Image 10

The measurement is shown as in image 11.

Image 11 Measurement measured by software

Distance shown in software is 20.058 m.

Slope percentage (S%) is calculated by dividing the rise to horizontal distance. The illustration is explained based on image 12.

Image 12 *image drawn is not based on real scale

The OGL can be obtained from the software by adding false nodes to each end of the arrow as shown in image 13 (node 9: 33.067m, node 10: 32.932m)

Image 13 False nodes are added to determine the OGL

Calculation = rise/horizontal distance x 100

= (0.135/20.058) x 100

= 0.67 % (refer image 4)

Calculation spreadsheet is attached as per link. Choose n, input L and S, then click ENTER to calculate t0.