The Watershed : lines transform operation creates Watersheds lines, which are lines that show networks of streams into which water flows within a region of common drainage.
This topic should be read together with other watershed topics:
Watershed Prepare: Filling Sinks - Fill sinks in preparation for subsequent watershed analysis.
Example: Create Watershed Areas - Create areas that show regions of common drainage.
Shreve Order and Strahler Order - Systems to assign a number to each watershed area or stream line which indicates at what level it lies within the branching hierarchy of the overall drainage system.
Watershed Areas, Sinks - Create areas for regions that are sinks, that is, closed drainage basins or pits.
Upstream Areas and Lines - Given a terrain image and a drawing of points, find the drainage basins and the stream lines from which water flows into each point.
Downstream Lines - Given a terrain image and a drawing of points, find the stream line for each point by which water issuing from the point flows further downstream.
Flow Direction and Accumulation - A topic showing an easy use of SQL to compute flow direction and accumulation.
We begin with the Montara terrain elevation surface, seen below, as used in the Watersheds topic.
With the focus on the surface, in the Transform pane we choose the Montara image and we choose the Tile field. We double-click on the Watershed template to launch it in the Transform pane.
In the Watershed template, we choose channel 0 as the Channel. Single channel images (as often are used for terrain elevation data) will automatically have channel 0 loaded into the Channel box.
As an Output option we choose the areas operation. We enter 500 for Minimum flow. We specify Watershed lines 500 for the name of the New drawing to be created by the template. As we enter the name for the drawing, the pane will automatically fill in an analogous name for the table. We can change that if we like.
For a preview of what the template will do, press Preview.
Pressing the Preview button shows the previewed results of the operation using blue preview colors. Previews are shown on top of all map layers. A blue preview caption bar appears at the top of the window with the name of the template used for the preview. We can right-click the caption bar for a pull down menu of options that control the preview. For example, to close the preview, we can right-click on the caption bar and choose Hide Preview.
If we would like to see only the preview without the Montara layer, we can double-click the Montara tab to turn off that layer.
To apply the transform operation, press Transform.
A new drawing called Watershed lines 500 appears in the Project pane. We drag and drop the new Watershed lines 500 drawing into the map as a layer:
The new layer appears in the map using default formatting. Each watershed line is a drainage stream that has 500 or more total flow units.
No watershed lines continue through Pilarcitos Lake because the "lake" is actually a reservoir, walled off from flow further downstream by a dam. In hydrology terminology it is a sink, that is, a catchment basin from which there is no onward flow.
We could have used the Watershed Prepare transform template to eliminate sinks in the terrain, for continuous stream lines in the region of Pilarcitos Lake as well. See the discussion in the Watershed Areas, Sinks topic and in the and the Watershed Prepare template.
Opening the drawing's table, we can see the fields created by the template. The total flow carried by each watershed line from the basin it drains is given by the Value field. The total flow through each watershed line including all flow from upstream watershed lines as well as flow from within the basin that line drains, is given by the ValueSum field.
To better see the lines, we will color them blue and make them thicker. We can do that with the Line stroke color button in the Style pane. We also increase line size to 1.5 points.
That shows the watershed lines in the terrain in blue color. If we like, we can color them using a thematic format on the ValueSum field.
We can style the watershed lines using a thematic format that colors the areas in a range from white to dark blue, based on the ValueSum value for each line.
To better see the watershed lines, we add a version of the Montara layer that has been styled in darker grayscale colors, called Montara Dark Gray. In the illustration above, as watershed lines change color from white to darker blue, we can see how the total flow in the stream increases.
Zooming to the detail area shown at the beginning of this topic we can turn on the areas layer to see how watershed areas and watershed lines are related. The area borders show ridge lines between drainage regions, while the watershed lines show the groove of valleys through which water flows in streams, which is why watershed lines are often referred to as stream lines.
Only those lines that have a minimum flow of 500 have been created, so watershed areas where the flow in streams running downhill is less than 500 do not have watershed lines in them.
Manifold vs Arc - Fifty times Faster than Spatial Analyst - The first video in a series of comparisons. We compare Manifold Release 9 to ESRI's ArcMap with Spatial Analyst. ArcMap instead of ArcGIS Pro is used to ensure maximum possible speed with no slowdowns from AGOL connections. Starting with a terrain 5300 x 5300 elevation raster we compare Manifold workflow and speed creating streams (watershed lines) with ESRI ArcMap and Spatial Analyst doing the same task. ArcMap requires four operations calculating intermediate steps, taking a total of three minutes and 30 seconds to compute streams. Manifold does the same job in a single operation in under four seconds, over fifty times faster than Arc, and with the convenience of a single click. ArcMap plus Spatial Analyst cost over $5000 per seat while Manifold costs under $500. As data sizes scale up, Manifold gets even faster than Arc. Works in the free Viewer, too!
Manifold vs Arc - Watersheds Sixty Five times Faster than Arc - Another video comparing Manifold speed to ESRI ArcMap with Spatial Analyst, this time computing upstream watersheds on a 5300 x 5300 terrain elevation raster for a few dozen locations. ArcMap requires three geoprocessing tool operations calculating intermediate steps, taking a minute and a half. Manifold does the same job in a single click in less than 1.4 seconds, over 65 times faster than ESRI. The larger and more complex the geoprocessing, the greater Manifold's speed advantage. ArcMap plus Spatial Analyst cost over $5000 per seat while Manifold costs under $500. Works in the free Viewer, too!
Manifold vs Arc - Seven Seconds vs Four Minutes - Finding basins in a 5300 x 5300 terrain elevation raster, we compare Manifold workflow speed and ease of workflow to ESRI's ArcMap with Spatial Analyst. ArcMap Standard plus Spatial Analyst costs a total of $5250 so it should work better than a Manifold package that sells for under $500, right? No way! Manifold absolutely crushes the comparison, taking only a single click and seven seconds to do what takes the $5000+ package three geoprocessing operations and four minutes, not counting the time to setup and launch three operations. Works in the free Viewer, too!
Manifold vs Arc - 100x Faster on an Affordable Desktop - Watch Manifold do in 0.9 seconds what takes ArcMap plus Spatial Analyst over a minute and a half. That's over 100 times faster! Some comments on previous comparisons have stated that Manifold was so super fast compared to ESRI because tests were run on a high-end, Threadripper machine that could run 48 threads. This video shows Manifold is faster even with fewer cores on an affordable desktop system. We re-run Manifold trials on a Ryzen 9 3900x computer, with three different tasks taking only 0.9 seconds, 5.4 seconds and 3 seconds. AMD's 3900x CPU now retails for as low as $450, setting a new baseline for affordable GIS desktop computing. Everything shown in the video works in the free Viewer, too!
Example: Create Watershed Areas
Shreve Order and Strahler Order
Watershed Prepare: Filling Sinks
Flow Direction and Accumulation