Procedural water generation

one way to do this would be to have a plane set at where the water level would be, but locked to the position of the airplanes x and z. then just animate the texture to scroll across the water plane at the rate and direction of the airplane.

i have a script that scrolls a texture on a RawImage UI canvas. it would take some editing, but you could use that as a base if you want to take that route.

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 
 public class ImageSroller : MonoBehaviour {
     
     public bool lockEdges = true;
     public float rate = 1f;
     public KeyCode positve;
     public KeyCode negitive;
     Vector2 offset = new Vector2(0f,0f);
     public Vector2 direction = new Vector2(0f,0f);
     public RawImage picture;
     
     // Use this for initialization
     void Start () {
         
     }
     
     // Update is called once per frame
     void Update () {
         float dir = 0f;
         if (Input.GetKey(positve)){
             dir += rate;
         }
         if (Input.GetKey(negitive)){
             dir -= rate;
         }
         Rect r = picture.uvRect;
         offset.x = (offset.x+(direction.x*dir)*Time.deltaTime)%1;
         offset.y = (offset.y+(direction.y*dir)*Time.deltaTime)%1;
         if (lockEdges){
             if (offset.x >= 1-picture.uvRect.width){
                 offset.x = 1-picture.uvRect.width;
             }
             if (offset.y >= 1-picture.uvRect.height){
                 offset.y = 1-picture.uvRect.height;
             }
             if (offset.x <= 0){
                 offset.x = 0;
             }
             if (offset.y <= 0){
                 offset.y = 0;
             }
         }
         r.position = offset;
         picture.uvRect = r;
     }
 }