flow systems, root systems from trees, and vegetative species can suffer from the amounts of soil being removed beneath them, and these stresses lead to surface erosion. Abandoned mines are also an issue with regards to areas where residential development has moved in. Houses erected near abandoned longwall mines face the threat of future damage from sinkholes and poor soil quality, even up to thirty years after mine abandonment. Since longwall mining is namely, very long, it can effect areas of over . Over these largest spans, it has been observed that longwall mines underlying mountain sides demonstrate more visible subsidence in mountain landscapes than it does for valley landscapes. There have been cases of surface subsidence altering the landscape above the mines. At Newstan Colliery in New South Wales, Australia "the surface has dropped by as much as five metres in places" above a multi-level mine. In some cases the subsidence causes damage to natural features such as drainage to water courses or man-made structures such as roads and buildings. "Douglas Park Drive was closed for four weeks because longwall panels ... destabilised the road. In 2000, the State Government stopped mining when it came within 600 metres from the twin bridges. A year later there were reports of 40-centimetre gaps appearing in the road, and the bridge had to be jacked sideways to realign it." A 2005 geotechnical report commissioned by the Roads & Traffic Authority warned that "subsidence could happen suddenly and occur over many years". However, there are several mines, which were successfully mined with little to no measurable surface subsidence including mines under lakes, oceans, important water catchments and environmentally sensitive areas. Subsidence is minimised by increasing the block's adjacent chain pillar widths, decreasing extracted block widths and heights, and by giving consideration to the depth of cover as well as competency and thickness of overlying strata. Fracturing and water quality Longwall mining can result in geological disruptions in the rockbed, and can in turn affect water movement and result in water moving away from the surface, through the mined area, and into the aquifer. A resulting loss in surface water can negatively impact riparian ecosystems. On top of this, if there are present dams near to the longwall mining site, this could doubly impact the riparian ecosystems as it would have a reduced inflow rate as well as the loss to the underlying rock