tx_skyrim_mud_01.dds is a landscape texture that's already used in SHotN, but it's added in Sky_Main.esm instead of Tamriel_Data.esm. This is an esp to add the texture to TD. The texture itself is already in TD.
Needed for the Druadach Highlands/Grey Plains part of HR427 (and probably eventually to fix it's use in SHotN).