i don't think you'll need to calculate with traces of the water height, if you just stored a global water height, then have an array 100*100 to store the water height in those areas, then:
if(global_water_height < node.water_height){
do some pumping... isn't that the effect you're trying to achieve? :\

hmmm, is the "dijk" always going to be put in the same place or can the player choose where to put it?

If it is only in one place then you can use 2 models for either side of the water, and then lower/raise them.

the dijk can be put everywhere and the white other size different shape etc. because the player change the terain en then i calulate the difference

mrguest i have somthihng like that but i dont know how to calucate if there is water ore not and because teh dijk nomraly has realy not normal shape but just every shape there is posible

and i want more then 100*100 lets say 1000*1000 and higher

thx slowglider

*dynamically resize water entities
*split water entities -> two from one
---than remove one on side of ditch
*join water entities -> one from two
---remove extra
*tile system
---raise lower terrain in chunks
---smooth chunks for hills / ditches (ramp procedure)
---save out to hmp / mdl format
*system to store water entity chunk states (with tile system)
---3d bounding checks (cube, etc.)
---on raise
------if intersection
----------split water entity
----------two from one
----------scale / translate two water entities
Other than that:
Quoting Michael_Schwarz.

Okey, I can't resist, too, to solve this question!

My suggestion:
- 2 big identical terrains: one for the ground, one for the water.
- 2 times: one before pumping, one after starting to pump

- the dike is build by rising the vertices of the ground terrain, until they are above the water terrain
- when the dike is closed/complete, the water vertices test whether the corresponding vertices of the ground is under it, and if it id, it is written in a list
- then you have to place a pump on the dike with the direction from land to ocean, this pump should have two parts, each part on one side of the dike: one part for the 'in' side (the land), one part for the 'out' side (the ocean)
- now, each vertex of the water traces to the pump; when it reaches the pump at its out side, it is written in a list of the 'ocean vertices', vice versa
in case it doesn't reach the pump, but the ground terrain is in its way, it traces to each vertex of the 'ocean vertices' until it reaches one of them, then it is written into the 'ocean list', if it doesn't reach any of that vertices, it traces to the 'land vertices' until it reaches one of them, and it can be added to the list.

Now, you have to lists of vertices which you can tread depending it belongs to the ocean or to the to be drained land side!