private void GenerateRivers()
{
_rivers = new Grid<bool>( _gridSize );
var line = new Line( new Point( 18, 1 ), new Point( _gridSize.Width - 20, _gridSize.Height - 1 ) );
var points = line.DrunkenWalk( 0.75, _rivers.Bounds ).Distinct();
foreach( var point in points ) {
_rivers[ point ] = true;
}
}