vcmi/config/rivers.json

{
    "waterRiver":
    {
        "index": 1,
        "text" : "Water river",
        "shortIdentifier": "rw", //must be 2 characters
        "tilesFilename": "clrrvr",
        "delta": "clrdelt"
    },
    "iceRiver":
    {
        "index": 2,
        "text" : "Ice river",
        "shortIdentifier": "ri",
        "tilesFilename": "icyrvr",
        "delta": "icedelt"
    },
    "mudRiver":
    {
        "index": 3,
        "text" : "Mud river",
        "shortIdentifier": "rm",
        "tilesFilename": "mudrvr",
        "delta": "muddelt"
    },
    "lavaRiver":
    {
        "index": 4,
        "text" : "Lava river",
        "shortIdentifier": "rl",
        "tilesFilename": "lavrvr",
        "delta": "lavdelt"
    }
}