Drainage FAQ — Shoalhaven

Mostly the size of the job and how hard it is to get at, from clearing one blocked stormwater pit to a full subsoil drain around a house. Relining a damaged pipe is usually priced per metre plus a set-up charge that applies whatever the length, so a short section costs more per metre than a long one. Digging it up and replacing it is usually dearer again. Paperwork can add cost too. Where a development application proposes soaking stormwater into the ground, Chapter G2 of the Shoalhaven DCP 2014 requires a geotechnical report. Get two or three quotes, and ask each contractor to run a drain camera through the pipe before pricing it.

Only under certain conditions. A charged line is a sealed pipe that relies on gutter height to push roof water out at the kerb, for blocks that fall away from the street. Chapter G2 of Shoalhaven City Council's DCP 2014 allows one only where no road gutter, table drain or drainage easement is available and the site will have at most two dwellings. The development application needs the adjoining owners' written acknowledgement that they refused a drainage easement after being offered reasonable compensation. It must show at least 1.8 m of fall from the roof gutters to the front boundary, plus fall from the boundary to the kerb, and a detailed design with a longitudinal section.

Two different things get called flooding. Water that sits for hours after a downpour often comes down to ground graded toward the house, or an old ag drain that has silted up, and a contractor can dig a test pit or run a camera through the pipes to find which. Bureau of Meteorology averages for Nowra RAN Air Station put February and March as the wettest months there. River and creek flooding is separate. Chapter G9 of the Shoalhaven DCP 2014 sets flood controls for each adopted floodplain plan, including the Broughton Creek plan for Berry and the Nowra and Browns Creeks plan for Nowra. Check which plan covers your property before earthworks.

Stormwater drainage carries rain off roofs, paving and the surface of the yard to the street system or another legal point of discharge. Subsoil (ag) drainage sits underground, usually as slotted pipe in a geotextile sock and gravel, and catches groundwater moving through the soil before it reaches your footings or gets under a slab. That matters because water sitting against footings softens the soil underneath, and on reactive clay it can make the ground move unevenly, which shows up as cracked walls and doors that stop closing properly. Most wet-yard problems need both looked at, not just one.

Shoalhaven City Council says there are more than 7,000 on-site sewage management systems in the Shoalhaven. The three most common types are septic tank (absorption) systems, aerated wastewater treatment systems (AWTS) with irrigation, and effluent pump-out systems. Running one needs an Approval to Operate, applied for only through the NSW Planning Portal, not directly with Council. Council inspects systems every five years, or more often for high-risk ones. For absorption trenches, Chapter G8 of the Shoalhaven DCP 2014 requires at least 1.2 m to groundwater and 1.2 m of soil above bedrock, with smaller separations for secondary-treated, disinfected effluent or the base of a mound. Treatment systems and application areas must sit above the 1-in-20-year flood level.

Council's stormwater chapter names it specifically. Chapter G2 of the Shoalhaven DCP 2014 notes that the Sydney drinking water catchment planning controls, cited there as SEPP (Sydney Drinking Water Catchment) 2011, apply to land at Kangaroo Valley and parts of the Sassafras area. If your property is there, say so in your enquiry, and check with Shoalhaven City Council what applies before any stormwater or effluent work starts. Separately, Chapter G8 of the same DCP requires effluent land application systems to be kept 100 m from permanent surface waters and groundwater bores, and 40 m from other waters such as farm dams.