Summer Concerns; Irrigation in the Arboretum

Centenary College, "Where the sleepy, silver bayou, / Gleams among the pines...." The Alma Mater says that the campus once had a bayou. What happened to it? There are still a few big pine trees, but much has changed over the past hundred years. 

The growth of modern cities with their necessary infrastructure of concrete streets & sewerage has greatly altered local hydrology. Whereas in the past rains might saturate a richly developed soil, rainwater is now swiftly funneled across impermeable barriers of roof-and-road into storm sewers and drainage canals. For our purposes here this means that despite getting on average 50+ inches of rain per year, summer conditions can easily cause drought. Since we need to keep our wide array of arboretum species alive for academic purposes and keep the non-native grass alive for aesthetics, this means we need to supplement our natural precipitation with artificial irrigation, mostly in the form of sprinklers.

An in-ground network of pipes supplies well water to most of the arboretum, and much of that system can be programmed to run automatically. Some lines of irrigation must be manually turned on, and water hoses must be hauled and stretched to reach a few small patches.

The sprinkler system is an absolute necessity for maintaining the health of the arboretum. The fact that it can provide an amusing diversion is a nice side-benefit.

Spring Rain

Several days of alternating light, steady, and heavy rains have resulted in a soaked arboretum. It's the first of May, and we have yet to turn on the arboretum's irrigation system. For the coming week, there is even more rain in the forecast. Below are photos from today, May 4, 2019.

On the north side of the arboretum, rain water swiftly runs its established course over landscape rocks.

These large rocks, or mini-boulders, are not original to the grounds of the college; they were added to the landscape when the arboretum was founded. Fast-growing vines, such as our Virginia creeper, work to conceal these mini-boulders.

On the northeast side, a brick retaining wall encloses the arboretum. Water passes through this wall and into the arboretum at several points.

Hamilton Hall and Mickle Hall stand on the opposite side of the retaining wall. A series of drains collects water from around these massive buildings and redirects it into the arboretum. The upper pond receives much of this runoff.

When the arboretum was founded in 1984, the upper pond was designed as a permanent aquatic habitat. Over the years, due to environmental difficulties, adjustments were made to allow for more flow and less retention. Today, the upper pond serves as a floodplain. It's inundated during heavy rains and allows for the slow absorption of water over a wide area. It's rare to have standing water in the pond for more than a week.

Runoff from the west side of campus also drains into the arboretum. The well-defined drainage channels outside of the arboretum divert excess water away from buildings.

Once the runoff enters the arboretum, its flow is slowed by less-defined drainage channels and specific planting choices to allow for more absorption.

This is the west floodplain. On a day like today, with heavy rain, two inches of water can easily accumulate across a wide area. Tomorrow, the ground will assuredly be soggy but we do not expect to see much standing water.

This narrow, overgrown channel is where the water flow from the west meets the water flow from the north.

In the arboretum, we like to keep more vegetation surrounding the drainage channels. There are two main reasons for doing so. First, the extra vegetation slows and reduces runoff, which pleases our water loving trees. Second, the plant life keeps the soil in place, reducing erosion.

Of course, a great deal of runoff occurs despite the purposeful landscape features, i.e., ponds, floodplains, and overgrown channels. Excess water quickly drains out of the arboretum and off campus via this concrete floodway.

Water in the Arboretum

Although it's not always flowing, the arboretum has a well-defined stream. After a substantial rainshower, you can appreciate some beautiful spots. Join us as we preserve the scenic character of the arboretum's ephemeral water features.

 

A main source for water in the arboretum is drainage. Here we see a culvert (near the SUB) that marks the beginning of the main artery of the arboretum's stream.

Water under the bridge: the roots belong to the Pumpkin Ash (Fraxinus profunda).

The stream crosses under several bridges, of which this is only the first.

In the upper pond, water accumulates to nourish a variety of species including palmettos.

And especially the Louisiana iris.

Trees happily throw roots into the eroded path of the stream, insuring access to water during rainstorms.

It doesn't take much rainfall to fill up these little pools. Over the next few days, evaporation and infiltration do their work.

These large pieces of concrete (remnants of construction around the Fitness Center) provide varied habitat for small snakes, amphibians, various creepies and crawlies.

What can you see in the reflecting pools?

This is the final stretch of the stream's main artery before it empties out into the concrete spillway near the Fitness Center.

From this point, excess water enters the storm sewers of the City of Shreveport. Au revoir, les eaux de la vie.