The Molonglo Valley is not flat and that is well known but it does cause problems. In Molonglo 3, on the north of the river, the gradients can be a challenge.
The Molonglo Valley estate development was planned in three stages, stages 1 and 2 south of the river and the biggest stage of all, stage 3, north of the river. Whitlam is the first suburb of stage 3.
It makes sense to build where it is flat. It is cheaper to build on flat land and easier to get around. ACT Education prefers flat sites for their schools. Community sports require ovals which need to be flat. The light rail, too, does not like steep hills. Flatland may be the best location for an estate development but – alas – Molonglo Valley is not flat.
Molonglo Valley is creating challenges for the ACT Government. Flattening the land through terraforming can be done as it was done in Whitlam, but it is neither cheap nor popular. There are also limits to what can be done. The Molonglo River has dug itself deep into the landscape and gradients close to the river can exceed 20%! Building in the Molonglo Valley was always only viable on the flat areas.
Further issues are caused by water. New residents do not want to see their houses flooded. Vast quantities of water are capture on the ridge of hills that separate Belconnen valley from the Molonglo Valley. The water flows pretty much straight off the hills under William Hovell Drive into two creeks: Deep Creek, following through Whitlam, and Coppins Creek on the other side of John Gorton Drive. The area north of William Hovell Drive is a large nature reserve. The runoff needs to be captured and filtered before release into the Molonglo River. Large dams to be built along the creek lines in Molonglo 3 for this purpose. The first dam with a volume of 132 megalitres will be built in Whitlam. It will not be the last, however, as Coppins Creek will also require civil works.
The design of the pond is currently underway. Early designs estimate that the pond embankment will be approximately 270 m long, 17.5 m high from the base of the pond and 18 m wide at the road crossing. The top of the pond embankment will include a two-lane road and pedestrian and cyclist paths.
Once full the pond is estimated to have a surface area of 63,200 m2 and hold 132,130 m3 (132 megalitres) of water.Lower Deep Creek Pond Project Update, ACT Suburban Land Agency, accessed 12 May 2021
Molonglo 3 estate is challenged by the steep slopes and large quantities of water. Unfortunately, the two do not mix. Large quantities of water, flowing down a steep slope, has considerable destructive force. The management of the water has a significant impact on the design of the suburb.
The implications of these restrictions can be seen in Whitlam. Whitlam was extensively terraformed, the hill remains and the river valley untouched. Deep Creek will be made a lake. The valleys in between the ridges have been flattened and gradients reduced. The valley between is a basin with steep edges, too costly for construction. A park is on the top of the ridge. Roads follow the contours, for the most part, and connecting roads climb the gradient.
Molonglo Valley estate is challenged by river crossings. Normally, the bridge would be located to keep the road gradient as flat as possible. Cars can climb hills but flatter is still better. The original Molonglo Valley Concept Plan saw the John Gorton Drive sweep through Molonglo to cross at Coppins Creek, before following the creek line to Bindubi Street. This would have connected Molonglo to Belconnen and CBR Cycle Route C5 up Aranda hill. John Gorton Drive will now be built over Coppins Crossing and Coppins Crossing Road. The road is steeper than it otherwise would have been.
While the reasons for the changes in the Concept Plan are unknown, difficulties with getting environmental approvals for bridges over the Molonglo River are well documented. The environmental approvals add time, cost and complexity to building the bridge. Federal environmental law produced the NES Plan, followed by the ACT Molonglo River Reserve Management Plan. Offset areas were finalised, such as Block GG beside the National Arboretum. Kama Nature Reserve moved from Canberra Nature Park to be included in the Molonglo River Reserve. Specific areas of the reserve required further study, such as the Kama, resulting in a protection zone separating it from Whitlam. Geological studies were conducted on rock outcrops around Coppins Crossing and much more. The John Gorton Drive Bridge got the exemption in the end, but only with provisions. The approval for the second river crossing (east crossing) is likely to take just as long.
The first implication is that the gradients are not all that suitable for cycling. The second point is that there are very few places that a cyclist can cross the river. You may also wish to read further about the Molonglo River Reserve Plan.