The following is Part II of a three part series focusing on the City of Scottsbluff’s 319 grant projects. These projects are designed to reduce impervious cover in parking lots, filtering and infiltrating stormwater runoff. This article will go over challenges and lessons learned from the projects. For an overview of the projects, see Part I.
In our last article, we went over the process of removing concrete and installing landscaping to create green areas throughout our downtown parking lots. There are several factors that, when combined, make it extremely difficult for a landscape to be successful in an urban environment. The following is a list of those challenges, along with a few of the lessons that we have learned so far. Over time, we will be continuing to observe and experiment with these landscapes to determine the best ways to make them successful.
Urban Landscaping Challenges
- Heat- Because the lots have so much impervious surface and little existing plant material, they get extremely hot. The addition of trees and other plant material will help cool the lot over time, but until the trees mature, it will be a very difficult environment for plants. We have attempted to choose plants that will tolerate these extreme temperatures, and have used mulch to help moderate soil temperatures, but it is impossible to moderate the pavement temperatures.
- Poor Soils- The areas we landscaped were under concrete or asphalt for many years. As a result, the underlying soils had no organic content, and because the sites had been developed and redeveloped, it was obvious that these soils were no longer the sandy soils that are native to the area, but were fill soils. Some of the project areas had such poor soils that we removed them and brought in fill, while others were slightly better, so we simply added compost to increase the organic content of the soils. We found that the areas where we brought in fill have tended to thrive better than the areas that we amended, although the areas with fill dirt also have far more weeds.
- Mulch- While the projects have been successful in directing a large amount of stormwater to the landscaped areas, the addition of standing water to the landscape makes mulching a challenge. We prefer organic mulch because it stays cooler and breaks down over time, helping to build up our soils, but this type of mulch floats in water, and keeping it all within the project is a challenge. We have discovered that using a more finely cut mulch helps to keep our little perennials and grasses from being completely buried when the mulch is shifted around by the water.
- Traffic- There is a lot of foot traffic through these projects, and even though we put cables up to keep cars out, we have also had a number of vehicles that have driven through the landscaped areas, breaking off the cables and damaging our plants and drip systems. In some of the areas that get the most foot traffic, we have tried to add pavers to accommodate traffic and direct it away from planted areas.
- Litter- Our projects have been capturing large amounts of litter. Fast food wrappers, paper cups, and cigarette butts are some of the most common types of litter that is collected by our rain gardens. While the larger pieces of trash can be picked out and thrown away, the cigarette butts are so numerous that we are going to leave them in place. We will be observing them over time to see if they break down. The bright side to this is that we are capturing so much trash and cigarette butts that otherwise would have been washed into the North Platte River.
- Vandalism- We have had numerous incidents of vandalism. Some of these are fairly minor, like when someone cut all of the wires that we were using to stake our trees, and some are more damaging, like when someone ripped one of the trees completely out of the ground and left it on the pavement.
Now that we have looked at some of the challenges to our stormwater projects, we will be looking at project successes in Part III of this series.