Rain Gardens and Wildlife Ponds
One of the major habitat elements, after food and shelter, comes water. There are two main routes that can provide water, a pond provides constant water while a rain garden provides constantly changing levels of water. There are many great resources for design and installation of both options.
If the goal is to provide habitat for frogs or dragonflies, a pond is most likely necessary because they require a constant water supply for the various life cycle needs. Dragonflies lay eggs in water where they hatch and live out the majority of their lives as nymphs before becoming dragonflies for a few weeks. Frogs also require water for tadpoles to live in before becoming adults. One of the best references for creating a garden pond is a document called Create a Garden Pond for Wildlife from Oregon State University Extension Service. There is also a good chapter on ponds in the book Landscaping for Wildlife in the Pacific Northwest with the same information on the WDFW website about The Backyard Wildlife Pond.
Much of the information is the same all three resources, and greatly detailed. There is a lot to consider when designing a pond, such as soil type, utilities location, sun/shade, liner types, edging and so on. Both of these resources cover all of these topics and more. Designing a pond for wildlife is much different than traditional landscape ponds, but with much better results. Some of the design principles include shallow areas for foraging and warming, gradual slopes for escape and deep areas for hiding or hibernating. The area directly surrounding the pond is also an important focus, because vegetation, rocks and wood give wildlife somewhere to bask, escape to or lay eggs on. There are other considerations which both resources address such as the problem with introducing wildlife or exotic fish. For example, buying tadpoles often means you’re introducing the problematic Bullfrog to a pond which will eat native tadpoles, nymphs and pretty much everything else that finds it’s way to the pond.
I would not recommend using the NRCS Backyard Pond publication because it offers suggestions that directly conflict with the other resources such as buying rigid pond liners in pre-made shapes. These types of liners do not offer the gradual slope and shallow steps that are necessary for wildlife escape, basking and feeding and are not recommended. They also suggest adding fish, but in doing so, the amount of wildlife that will survive is greatly reduced because the fish will eat eggs, larva and nymphs of various aquatic species.
Rain gardens serve several purposes in addition to providing habitat. They reduce the speed of rainfall entering stormwater systems and serve to more closely mimic the natural hydrological cycle. In our built environment we have a great amount of impervious surface space in roofs, parking lots, roads and sidewalks. In a natural area, such as a forested area, the surface runoff from rain water is only about 10%, while in a suburban area, it’s more like 30% and up to 55% in urban areas. Our existing system is designed to get it into the storm drains and out to streams as fast as possible. This causes many problems such as flooding, which can be a severe problem on systems where stormwater and sewage are combined. Runoff also picks up a great amount of pollutants including pesticides, oils, toxins, animal waste, heavy metals and more. By holding water in rain gardens, it gives the rain water time to infiltrate into the soil and replenish aquifers. Rain gardens also function to help filter out pollutants before water enters the ground or the stormwater system.
If you want to learn more about the hydrologic cycle, you can read a paper I wrote about it on the previous post. The Hydrologic Cycle
Aside from the stormwater benefit, rain gardens provide habitat as well. One of the resources listed below has an excellent description about how rain gardens provide habitat:
It is easy to think of garden wildlife as being visible and attractive things that we all like – birds and butterflies. But in reality garden biodiversity is largely about the things we can’t see, or which are not prominent – insects and other invertebrates, hidden away beneath the vegetation or in the soil. The big things we like have to live off the small things we cannot see. Rain gardens are particularly useful for supporting that greater biodiversity. Leaving the stems of perennials and grasses standing over the winter will provide a home for many invertebrates, as well as food for seed-eating birds. The diversity of flowers will provide nectar sources, particularly in the late summer and autumn. – Rain Gardens: Managing water sustainably in the garden and designed landscapes
There are three really excellent resources about designing, installing and maintaining rain gardens, and two of them are free. The first is called Rain Garden Handbook for Western Washington Homeowners and the second is The Oregon Rain Garden Guide. They both have more or less the same information, but the Oregon book is good because it breaks down all of the regions in Oregon and gives sample plans for each including central Oregon, southwest Oregon, Willamette Valley and Oregon coast and it has a great plant list with images and wildlife benefits for each plant. The Washington guide has a better installation section with many pictures documenting the various steps.
The third resource is a book by Nigel Dunnett and Andy Clayden called Rain Gardens: Managing Water Sustainably in the Garden and Designed Landscape. It covers rain gardens as described in the other two resources, but also a whole lot more. They discuss what they call, the Stormwater Chain which consists of the different levels of components that can be installed to manage stormwater, and nearly all can be used to provide habitat. The top level is the green roof, and then the green facade or green walls, down to rain barrels and stormwater planters. On the ground there can be porous pavement, rain gardens, swales and constructed wetlands. The book goes into great depth on each of these components and offers up a variety of case studies to illustrate each piece of the chain. One thing this book covers in much greater detail than the two handbooks mentioned above are conveyance techniques. In the two manuals they just mention getting water from the source, such as downspouts, to the rain garden. However, in this book there are many methods to convey water to the garden and many creative designs with illustrated images and photos. There is a lot of room for artistic design in the means of conveyance, and many creative solutions have already been designed and installed throughout the world.
Additionally, this book tackles the larger picture. The two handouts are written for homeowners, but this book provides a perspective on entire neighborhoods, campuses, streets and much larger landscapes. There are also plants listed in this book, but they’re aimed for the UK so they’re not regionally specific for the Pacific Northwest like the two handbooks above. This book is an excellent resource and encompasses much more than one might expect and I highly recommend it.
Create a Garden Pond for Wildlife:: Oregon State University Extension Service
The Backyard Wildlife Pond:: Washington Department of Fish and Wildlife
Rain Garden Handbook for Western Washington Homeowners:: Washington State University Extension
Rain Gardens: Managing Water Sustainably in the Garden and Designed Landscape:: Nigel Dunnett and Andy Clayden
The Hydrologic Cycle:: Kelly Brenner
Ponds for Wildlife:: RSPB
Rain Gardens: A Rain Garden Manual for South Carolina (PDF):: Clemson Public Service
Rain Gardens: Iowa Rain Garden Design and Installation Manual (PDF):: Iowa NRCS
Rain Gardens for Home Landscapes (PDF):: Clean Water Campaign, Georgia Department of Natural Resources