How to make the top shine

hello.
Using the method you suggested, I built a terrain and planted grass.
Thank you to everyone who has helped so far.
In this state, how did you make the top of the pool shine or darken the parts except for the top?
I used MeshStandardMaterial.

by me

other people
grass_other

Maybe you need normalMap and SAO map for those textures.
Or you can try post processing SAO.
Or maybe you can try directionalLight with enabled shadows
Or maybe you can just edit directly the texture and make it darker at the bottom with some image editor

thank you for reply