A rain garden, also called a bio-retention cell, is an attractive native plant garden with a special purpose, to reduce and filter the storm water entering our local waters. I designed three alternative designs that considered an aesthetic appeal, shape, surface area, and drainage methods (Nelson and Daigh, 2018). The three designs include a regular depressed EZ Rain Garden, a berm, and porous concrete. I will go into detail on each of these designs and in the end, I will recommend the first proposed design as the one that should be implemented here at EZ rain garden and explain why I thought it was the best one.
Project description
Our final design is a little out of the box when one thinks EZ Rain Gardens. Instead of having all the water diverted towards the garden through the drain I will install porous concrete on the side of the road down to the pipe where most of the runoff is located (Funai and Petr, 2019). Porous concrete-like conventional concrete is made from a mixture of cement, coarse aggregates, and water. However, it contains little or no fine aggregates like sand, which results in a porous open-cell structure that water passes through readily.
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The building of a Rain Garden requires an implementation plan that orders each step properly and tells concisely what needs to be done, and to what extent (Asleson et al. 2009). The implementation plan should take one from nothing but a list of supplies to a fully functioning Rain Garden. An important note: It is most effective to start the actual construction of the Rain Garden in the spring when the abundant rains will allow for the best plant establishment and easier digging. Construction during the summer/autumn start will also work, but the plants may need more water until they become established. To create an efficient Rain Garden, it must be sized appropriately.
To finish off the implementation of the rain garden, apply a layer of mulch over the entirety of the garden’s surface. Allow for 3” depth mulch to be spread throughout the entire rain garden. For every 100 square feet of the rain garden, you will need about 1 cubic yard of mulch (Nelson and Daigh, 2018). This means that, at the given values, about 10-11 yards of mulch will be necessary to cover the entire surface properly. All of these aforementioned steps help to bring about the full construction of a functioning rain garden. Though a relatively simple process, the design of the rain garden is broken down so that all steps can be related to any given area where such a rain garden is desired.
Materials
Determining the materials required to make a Rain Garden is the essential first step in the building process. Materials needed for the construction of a Rain Garden will include plants, top layer soil, sand, compost, hardwood mulch, limestone, bluestone, and construction/gardening tools (Asleson et al. 2009). In each case, there are multiple factors in deciding which type of each material is best. The types of plants selected are based on the general criteria of certain aspects of the garden. These include the amount of sun available, the temperature of the region, the average amount of rainfall, size of the plants, pH, and composition of the soil, among others. One important factor is to make sure that there are not too many or too few plants.
In some cases, the soil from the initial excavation can be used from the original site. However, to make nutritious bedding for the plants, sometimes new soil has to be brought in that is not contaminated or polluted (Funai and Petr, 2019). In most all professionally built Rain Gardens, new soil is brought in and used. It is estimated that a Rain Garden of approximately 800 square feet will need a total soil mixture of about 44 yards when dug down and refilled to a height of 18 inches below the surface. In the case of the Rain Garden designs on the EZ Rain Garden, the current soil is of a nutritious enough value that soil does not need to be brought in for this purpose.
Budgeting
However, with an average soil pH of 5.7 in the selected location, certain additives will have to be added to the soil to maintain a slightly higher level (Nelson and Daigh, 2018). We estimated that about 16-25 pounds of lime would be needed to be added to the soil to reach a desirable pH range of 6.1 – 6.5. A Pennington Fast-Acting Lime compound, in 30-pound bags, runs about 15 – 2- USD per bag. Regardless, it will be proposed that new soil be brought in, for the plants to have the best conditions for survival. In the Rain Garden proposal of 1036 square feet, it is estimated that about 57 yards of soil composition would be needed (if dug to the average depth).
Building/Implementing
However, the soil in itself would be about 14-15 yards of this total number. Adding a stone edging to a Rain Garden is a common practice (Asleson et al. 2009). Using ¾ inch cut bluestone, or other such rocks has several functions within a Rain Garden. This can both act as a visually appealing edging and a solid border. Again, this will provide both an extra layer of holding, while at the same time present a visually appealing front. About 3 yards of ¾ inch cut bluestone, at about 20 USD per yard, would be needed for each design.
Limestone is a commonly-used soil additive to increase the health and effectiveness of a Rain Garden. Most soil may need to be slightly more acidic than it naturally is for proper Rain Garden conditions (Funai and Petr, 2019). This is usually mixed into the soil mixture that is laid down in the garden. To finish off the implementation of the Rain Garden, apply a layer of mulch over the entirety of the garden’s surface. Allow for a 3” depth mulch to be spread throughout the entire Rain Garden. For every 100 square feet of Rain Garden, you will need about 1 cubic yard of mulch. This mulch layering will help to keep the soil layers below properly packed, and acts as a super-absorbent top layer to allow for the pooling of storm water.
Scheduling and Maintaining
Occasionally, trimming and mulching of excess foliage is required. Plants in rain gardens are built to prosper across the planting season. A barren desert is an essential component of the rain garden as it tends to absorb nutrients and penetrate water (Asleson et al. 2009). As with a normal garden, the rain garden may need more extensive and vigorous weeding for the first few years, until the required plants were properly established. Regular watering is most critical during the first few weeks after planting and very important during hot, dry periods during the first two years since cultivation.
Conclusion
Now that the regular EZ Rain Garden design, berm design, and porous concrete design have been presented I hope that the idea for each is clear. Since these designs are complete I am now ready to move on to the dissemination plan, which will allow us to spread the word about our EZ Rain Garden to the community.
References
Asleson, B. C., Nestingen, R. S., Gulliver, J. S., Hozalski, R. M., & Nieber, J. L. (2009). Performance Assessment of Rain Gardens 1. JAWRA Journal of the American Water Resources Association, 45(4), 1019-1031.
Funai, James T., and Petr Kupec. "Evaluation of Three Soil Blends to Improve Ornamental Plant Performance and Maintain Engineering Metrics in Bioremediating Rain Gardens." Water, Air, & Soil Pollution 230.1 (2019): 3.
Nelson, R. S., McGinnis, E. E., & Daigh, A. L. (2018). Rain Garden Sedges Tolerate Cyclical Flooding and Drought. HortScience, 53(11), 1669-1676.
Appendix
Figure: Final Presentation, morphing slide showing the preliminary AutoCAD design for a rain garden between Gordon Library and Fuller Laboratories.
Shown here is a potential design for the information stand to be located at the rain garden site. This stand will be placed at the railing along the access road in front of the library. This stand, to be erected before construction, can remain even after implementation of the garden as an educational tool and artistic piece to garner interest.
