The Watershed Approach to Landscaping

By Pamela Berstler

We know that our individual landscapes play a critical role in the health of both the watershed we live in and the earth as a whole, yet we often don’t see how the simple practices of gardening in our front yards could possibly influence climate change! We’re too little and the problem is too big, right?

The watershed approach (WA) to landscaping allows us to change landscapes, which are often thought of as “ornamental,” into multi-benefit environmental solutions.   But why the heck are we calling it “watershed” approach? It sounds so weird, and we’re used to “water wise.”

The use of the term “watershed” allows us to shift away from a water conservation-centric discussion of landscaping (which honestly feels like a lot of sacrifice) into a more integrated resources conversation (which feels like a change with big benefits).

The best thing about using the watershed approach on individual properties is that those properties now become part of a bigger solution, acting together to make communities more resilient.

What is a watershed

The Environmental Protection Agency defines a watershed as:

“An area land that drains to a common waterway, such as a stream, lake, estuary, wetland, aquifer, or even the ocean.”

Using this definition, any area of land, every property, regardless of size or land use (every front or back yard, every roof top) can be described and regenerated as a “mini-watershed” using agreed upon principles of watershed management.  These principles unite water managers, watershed managers and flood control, developers, landscapers, horticulturalists and property owners behind one mission that goes beyond sustainable and water wise principles. The best thing about using the watershed approach on individual properties is that those properties now become part of a bigger solution, acting together to make communities more resilient.

Why is the watershed approach important

The watershed approach sets new priorities for landscapes; these are:

1. The intention to gather as much rainwater as possible in every landscape, and
2. The intention to optimize the availability of water for cycling back into the atmosphere via evapotranspiration.

In nature, a healthy balanced watershed allows precipitation to pass through a highly-developed system of plants and “living soil” (soil alive with microbial and fungal activity) before it either moves through the system into a local waterway or groundwater, or is held in the soil profile for evapotranspiration by the plants.  The water that is slowed by plants and soil before moving into groundwater or nearby waterways is cleaned by the microbial activity of the plants and soil, so water quality is improved.  That water which is held in the soil, is transpired by the plants back into the atmosphere where it is able to continue the cycle of precipitation – eventually forming clouds, condensing, and falling back to earth.

Principles of the watershed approach

 After setting an intention to gather all the rainwater that falls on a property and put it into the soil, the principles of the watershed approach can be applied:

1. Build healthy living soil that is biologically diverse and has developed a structure like a sponge

This is best accomplished by adding organic matter to the soil.  Spongey soil structure is perhaps the most critical principle of the watershed approach to landscaping, as it primes the system for holding or releasing rainwater, sequestering and cycling carbon and nutrients, and promoting the incredible biodiversity that is necessary for plant resiliency. Also, a 1% increase in soil organic matter holds 16,000+ gallons of water per acre to a depth of one foot; that is a critical resource for plants to thrive during seasonal drought, and survive during extended dry conditions.

2. Treat rainwater as a resource rather than a waste product

Since our intention is to hold on to as much rainwater as possible, this may seem as a no-brainer.  It’s important to remember the simple methods by which rainwater is retained on a site. Retention is best accomplished by creating small divots, swales, basins, and contours.  Make sure that impermeable surfaces are either made permeable or used as capture areas for redirection of water into the landscape. When we treat rainwater as a resource, we need to plan for capturing ALL of the rainwater.  Rainbarrels and cisterns may be necessary to temporarily store quantities of rainwater that eventually can be released back into the landscape over time.

3. Plant climate appropriate plants, preferably local natives

Local natives are adapted to the soils, rainfall and weather patterns of a particular place.  They are symbiotic with the other flora in their community, and the fauna that rely on that community.  They also are symbiotic with the fauna and flora of the soils.  This makes local natives the very best choice for landscape resilience. Perhaps more importantly, local natives, planted in their natural communities, are able to work together by sharing carbon, water, and nutrient resources through a soil-based microbial and fungal network.

4. Use highly efficient irrigation, only when necessary

The “only when necessary” is important to think about.  If you are capturing rainwater, building healthy living soil, and selecting plants that are in sync with your local climate, you may not need to install an automatic irrigation system; in fact, rainwater passively collected in your soil may be your only source of water.  However, since climate change is altering weather patterns, even local native plants in the best biologically active soil will struggle during periods of prolonged drought.  That means, many California natives in garden settings will do best if provided supplemental water during the winter months if there is extended drought and during the fall through spring months, if rainfall is minimal.

Irrigation efficiency is determined by how effectively the water applied to a landscape actually gets to where it is meant to go. Drip irrigation emitters, low-flow valves, weather-based irrigation controllers, back flow preventers, low head check valves, and soil-based moisture sensors are all part of efficiently designed, installed, and managed irrigation systems.

Another aspect of efficient irrigation is the selection of the supplemental water source.  Irrigation that draws from rainwater or gray water is a better choice than a new system that uses drinking water. And finally, management of the irrigation system is critical!  Irrigation systems are not to be built and forgotten; they need to be actively and constantly managed in order to be watershed wise.

Applying the watershed approach

In future posts, we will discuss how healthy living soil contributes to the resilience of local native plants, and how watershed approach landscapes can alter weather patterns and contribute to reversing climate change.

Pamela Berstler is the CEO of G3, Green Gardens Group, Executive Director of Pacific Horticulture Society, and Founder of the Urban Soil Summit.