Why are creeks sometimes piped underground in urban areas?

Question

I live in Melbourne, Australia and a lot of the creeks here have been diverted through underground storm water pipes. I guessed that this is because land is highly sought after for development, and a lot of these creeks have been built over, however there are also a lot of cases where there is nothing built over the top of them at all. They simply carry the normal water flow through a small concrete pipe, leaving an empty valley on the surface which would only carry flood waters during heavy rainfall. What's the reason for going to the cost and effort of doing this?

Is it a safety concern having creeks in residential areas? Do creeks have some effect on the land which would affect nearby buildings? Is it just for the convenience of being able to cross them without a bridge?

Example

Dandenong Creek in Bayswater area @ -37.836524 lat, 145.254465 long (water flow goes from the right to the left of the image):

I've also seen a creek which briefly goes both above and below ground. The rushing water of the underground section could be seen through an overflow while the topside creek was mostly just stagnant water. It seemed completely pointless and made no sense to me.

Answer 1

In more developed areas (cities) burying streams is popular because it allows for more land to be developed without the fear of flooding. Also, streams in these areas tend to become very blighted and void of life. At that point you might as well hide them from sight.

The area that you show doesn't seem to be one of these areas. There are a few reasons that I can think of that might lead to the situation that you are describing.

Swampy Area

The area seems to be fairly flat. In its natural state, it may have been a swamp. Providing a buried pipe provides a freely draining area what will keep the water flowing in times of low flow. This will keep the area from being swampy and the negative aspects of that: mosquitoes and smell.

You can see from the satellite images that there are some drainage structures that will help surface water to flow into the buried pipe.

Park Areas

The grass above the stream can now be used as a park without worrying about the dangers of children playing around a stream. This makes the area dual purpose without completely reducing the flood control capacity of the area. In times of heavy rain, the area above the pipes can still be used to to retain excess water.

Slowly Fixing Past Mistakes

It could also be that at one time the stream was completely buried. The local authority might be slowly exposing the stream to restore the natural condition. Without knowing the timeline of the area, it it hard to tell if this is a possibility.

Answer 2

What's the reason for going to the cost and effort of doing this?

In many places, placing a stream into a culvert can be cheaper in the long run. Streams (particularly fast flowing ones) erode the land and may require erosion protection added in the future.

An advantage is reduced land use: Land that does not have a stream running through it can be used for other purposes, although the culvert will need to, obviously, be assessed before plomping (technical term..) a multi-storey car park on top of it!

Is it a safety concern having creeks in residential areas?

Highly dependent on the area in question and the nature of the creek or stream. Naturally, a stream is a hazard to people of all ages, particularly kids though. But so is a culvert if the access to it is not cordoned off. As answered previously, an open grassy pitch is more favourable than a flowing stream.

Do creeks have some effect on the land which would affect nearby buildings?

Creeks have a tendency to meander in the long term (decades to centuries), and deeply scour the nearby banks in the short term (years). Scoured banks can become steep and rocky, and even collapse. If there are buildings located nearby, then this can cause structural damage.

Is it just for the convenience of being able to cross them without a bridge?

As an engineer with Highway experience you'd be amazed at how many culverts manage water flow run under many of our roads. In Scotland, it's not unusual for there to be a 600mm diameter culvert every few hundred metres or so on many trunk roads and motorways helping ease water through them.

Most of the time, these are never seen or acknowledged as they can be down steep road verges. This is because these roads tend to be built very straight (much like railways), opposed to older roads that simply follow ancient paths and travelling routes.

A final note:

Culverts can be used to change the velocity of flowing water. For example if a stream has a narrow channel, the water will flow quickly causing it to quickly erode the bank. You can slow the water velocity in an area by passing it through a wide culvert. With a wider area of flow, the water will travel more slowly. This can cause advantages down stream. Similarly, the same effect can be caused upstream by forcing the water through a narrower passage. This will cause the water to back-up up stream reducing it's speed.