Inland / crater watershed delination

Question

Even though watershed delineation is a quite popular matter here, I have what seems to be a somewhat unusual demand.

I start with a DEM which is constituted of a series of craters, all centered on one point which is the lowest part of the crater.

Here is a picture of my DEM

What I want to to, is to obtain the drainage basin of each crater.

I know how to delineate watersheds using ArcGIS' Hydrology tools, but they are best suited for 'open' hydrological systems (flows try to reach the exterior of the raster).

Here is the result I obtain. How comes some of my drainage basins are obviously wrong? Why is Arcgis so lazy that its scope is limited to the rectangle limited by the four most extreme (N-S-W-E) points?

Therefore, my question is the following: is it possible to automatically delineate the watershed basin and set the center of my craters as the targets where my flows should go?

Thanks in advance for your help!

Damien

[Edit : added Arcgis output for clarity]

Answer 1

The default for the watershed tool is to limit the output extent to the same as your input pour points. You can change this in the Output Extent (Environment setting) to the maximum of inputs or same as the original DEM. For more info see The analysis environment of Spatial Analyst. Try the Snap Pour Point tool to see if this helps ensure that your crater centers are at the cell of highest flow accumulation (i.e. lowest spot in each crater).