The habitat and functionality of the Hollygrove and Midcity Rain Gardens

 by Stephanie Gross

This is a follow-up to the water chemistry post I made earlier this month. I have been monitoring a garden on Forshey St in Hollygrove and another on Wildair Dr in Midcity since April 2015, just about six months. The two sites have bowl shapes or deep ditches surrounded by native plants and grasses such as Taxodium distichum or cypress trees, Muhlenbergia capillaries which are known as Poas or grasses, Sabel minor also referred to as a palm or palmetto, Hymenocallis liriosme or spider lilies, and several Louisiana irises.


Above: The Forshey rain garden with cypress trees lining the garden, lilies and irises in the flower beds, and grasses behind the flower beds.


Above: Wildair rain garden with grasses seen towards the front left, irises in the water, spider lilies can be seen in the flower bed which also have grasses, and small cypresses are lining the exterior of the property.

I believe the gardens are functioning well, collecting water from rainfall and run-offs from the street. They are not only prevent flooding from large rain events, but also are filtering undesirable chemicals. Water chemistry data shows that low levels of phosphorus, nitrogen, and metals are detected with regular water sample collection. Additionally, I have never found standing water at either site 24 hours after a rain event, which is important for reducing mosquito activity.

There are a few undesirable issues, however. During an intense rain even in May, two cypress trees were damaged at the Wildair site.

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Above left: A cypress had to be pruned because high winds snapped the bark in two. Above right: A stake had to be attached to another cypress so that it would grow upright.

The cypresses are now looking healthier.

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Above left: The pruned cypress in June. Above right: Both the pruned cypress and the staked cypress look healthy in August.

The Wildair site also has a lot of soil erosion and loss of grass.

In terms of water collection, water was collected from the Wildair site at least once a month and only once in the past six months at the Forshey site. The Forshey site is not as bowled or depressed as the Wildair site, which may be affecting its functionality. Sure, one part of the city may have more rain than the other, but I do not believe that frequency of rain alone is affecting this difference in these two sites.

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Above: The dropbox at Forshey containing just a few millilitres of water earlier this month after a week’s worth of rain.

My observations are being shared with Water Works, Bayou Land RC&D, and the Mosquito & Termite Control and of course on this site. Data collection and progress reports are still being generated for continued study of these sites.

*click on images to make them larger*


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