Water edge seperate shader

Hi, kind of a tall order here... How would one go about making an independent seperate shader for the waters edge, similar to TGE's lighter colored water near the edge of the terrain.

Or better yet, a shader modifier based on altitude from the atlas object, so I can make water appear darker in deeper areas, and more transparent in shallow areas, that would be awesome :) (To use the waterObject.clarity variable, and modify it based on its direct distance from the ground.)

I'm trying to learn shaders here, and in the beginning of waterCubeReflectRefractP.hlsl there is

struct ConnectData
{
float4 texCoord : TEXCOORD0;
float3 lightVec : TEXCOORD1;
float2 texCoord2 : TEXCOORD2;
float4 texCoord3 : TEXCOORD3;
float2 fogCoord : TEXCOORD4;
float3 pos : TEXCOORD6;
float3 eyePos : TEXCOORD7;
};

My first thought on this is this; "ConnectData", is connecting the hlsl file with data retrieved form the game.

the float# is a floating point integer with # of number sets (i.e a float 3 should have 3 groups of numbers example: float3 position "0 0 0";)

So my guesses are that it retrieves your eye position, (eyePos), the direction light sources are coming from (lightVec), and the games position of the object its-self (pos) and some other variables I can't guess what they do yet (texture Coordinates)

Are my guesses right? How does it gather this info, is there a way to import any variable from the game engine into the hlsl file for usage there?

Many thanks for your time, hopefully if this gets done and looks great it'll make an excellent resource

-edit- Another question: Why are they all called "TEXCOORD#", I wish they were named more clearly, isn't that kind of like naming all your variables x y and z, and x2,y2,z2 etc? :) What does light Vector have to do with TexCoordinates?