Split Rock sub-catchment covers an area of 254 km2 with elevations ranging from 1000m to 400m near Split Rock Dam which is located between the towns of Barraba and Manilla. A number of small creeks and gullies drain into the dam including Crow Mountain and Eumur Creeks.
The Dam has a catchment area of 1,650km2 mostly from the Upper Manilla and Ironbark Creeks and a storage capacity of 75% of Sydney Harbour. As of September 2008 the dam was only 6% of capacity.
This sub-catchment and its dam supplies water for irrigation for the Namoi Valley, stock and domestic use on the lower Manilla River before joining the Namoi River and Keepit Dam.
Landforms range from undulating hills to steep hills with narrow valleys. Soils range from skeletal soils on the steep hills to shallow red brown earths on the lower slopes.
Soil erosion and gully incision are damaging processes in these landscapes. These naturally steep landscapes produce high levels of run off from rain and storm events. If there is insufficient pasture cover due to grazing livestock, sheet, rill (tiny gullies) and gully erosion will result.
Glen Riddle Reserve at the northern end of the dam is a recreation reserve popular with local fishers and Barraba residents whilst the reserve and dam at the southern end attract fishers, skiers, campers and tourists who enjoy the dramatic landscape.