Water, Air and Soil

Small watersheds are nested within each other to become larger ones. For example, the smallest watersheds collect water to form the headwaters of a creek or stream, which flow to rivers. Large rivers themselves are one big watershed that contain many smaller watersheds with streams that flow to the river. This nesting creates a sort of hierarchical system of a large watershed containing hundreds of sub-watersheds, and the sub-watersheds contain their own catchments (See Figure 4).

The US Forest Service uses a six-level watershed classification developed by the US Geological Survey called the hydrologic unit code (HUC). The six levels range from the largest to smallest: region, subregion, basin, sub-basin, catchment, and sub-catchment. In the first level, the largest region is given two digits, while each level below it adds another two digits to the HUC. The smallest sub-catchment has 12-digit codes.

Using the six-level watershed HUC system is useful to gauge the size and scope of watersheds. Since watersheds are nested well into one another, the specific HUCs can be traced back to the next level up with ease. (Perhaps we should add the USGS picture here? Picture at the end for reference).

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Figure 4: A major river system (pink) will contain regional watersheds thousands of miles in size. Each of the regional watersheds will have its own smaller rivers with their own watersheds. In this example, region 03 has a sub-region of 0306. The sub-region has basins, where the basins can be further divided into sub-basins with larger code numbers. USDA Forest Service image by Kelly Mott Lacroix.

Watersheds are important because they regulate the location of flow of rivers toward lakes and reservoirs. Water to the Tonto National Forest provides benefits to humans and wildlife, including drinking water, irrigation, wildlife habitat and biodiversity, and recreation.

Additionally, a healthy watershed brings in benefits like increased adaptability to climate change and wildfires, and improved water quality. Read more about the benefits of a healthy watershed.

The US Forest Service manages at the watershed level because the effects of a watershed have great effects on the forest. From the smallest sub-catchment to the largest basins, a watershed only has one point of drainage. As water flows downhill from the headwaters to the base level, the health of a watershed can have a cumulative impact further downstream. Indicators that contribute to a watershed’s health include but are not limited to water quality, amount of flow, soil condition, bank stability, riparian versus invasive vegetation, channel morphology, fire regime, and grazing.

The Tonto National Forest contains 181 sub-watersheds, where each one contains its own rating under the Watershed Condition Framework. The broad range of impacts to a sub-watershed require an interdisciplinary approach of specialists to assess and prioritize funding for the restoration of priority watersheds.

Watershed Condition Framework and Priority Watersheds

Beginning in 2011, watersheds across National Forest lands were classified under the US Forest Service Watershed Condition Framework. This framework was designed to be a consistent, comparable, and credible process for improving the health of watersheds across all National Forest lands. Watersheds were rated using a set of indicators of geomorphic, hydrologic, and biotic integrity relative to potential natural condition. The ratings are entered into a computer database, which generates an overall rating for each watershed. The results are also used to create a watershed condition map.

• 2011 Watershed Condition Framework
• 2011 - 2020 Watershed Condition Framework
  • The 2011-2020 report summarizes the accomplishments of first 10 years of the Watershed Condition Framework.

Priority watersheds are areas where the ecological and environmental value are greatest and given the highest priority for protection and/or improvement. In these priority watersheds, a Watershed Restoration Action Plan (WRAP) identifies specific projects necessary to improve the watershed condition class.

In the Watershed Restoration Action Plan, a list of special activities outlines the essential and complimentary projects to improve the condition of the watersheds, usually implemented within a five-year period. Essential projects are considered most valuable to improve the condition of a watershed, while complimentary projects help maintain the condition and help prevent further degradation of the watershed.

As an example, essential projects listed for Little Green Valley WRAP include:

• Installing a fence to keep elk out of the Fen area.
• Restoration and maintenance of the fen and meadow.
• Limiting public use of Forest roads in the Little Green Valley watershed and implementing erosion control BMPs.
• Decommission Forest roads to a natural state.

Secondary projects for the Green Valley WRAP include:

• Constructing water tanks away from the river to reduce grazing near the riparian zone
• Controlled burning to reduce vegetation overgrowth
• Monitoring of the area during and after implementation of the projects.
• Currently, the Tonto National Forest has three priority watersheds.

Downloadable documents:

1. WRAP for the East Verde Headwaters
2. WRAP for Green Valley
3. WRAP for Camp Creek will be completed soon.

Historically, wildfires are a beneficial way to maintain a forest. Wildfires clear out overgrowth and old and dead litter and introduce new nutrients to the soil to promote new growth.

However, the concerns of climate change have provided challenges to the Tonto National Forest Watershed staff. Drier monsoonal seasons, increased drought, and record-hot summers create more favorable conditions for large and severe burns. After a wildfire, the burned soil is unstable and unable to absorb water. Burned watersheds are dangerous areas during a rain event because rainfall runoff can bring ash and debris downstream to create devastating flash floods. Large flash floods can degrade the condition of riparian systems, displace the water capacity of our reservoirs, and pose a danger to life and property.

As wildfires become bigger and more common, the Tonto Watershed team will continue to provide post-fire assessments on watershed health and its implications to humans and wildlife. The Forest Service Burned Area Emergency Response (BAER) program addresses the above situations on Forest Service lands with the goal of guarding the safety of Forest visitors and employees and protecting Federal property, water quality, and critical natural or cultural resources from further damage after the fire is out. Information collected by the Forest Service BAER teams is shared with other Federal, State, and local emergency response agencies so they can provide assistance to communities and private landowners who may also be affected by potential post-fire damage.

Wildfires can have a consequential long-term effect on wildlife ecosystems. The most intense wildfires can leave burn scars that linger for decades, and plants that aren’t adapted to wildfires, like the saguaro cactus, may never recover at all without manmade reforestation efforts. However, some ecosystems still benefit from the clearing of crowded vegetation and the release of nutrients to the soil. Chapparal and mixed conifer environments have plants that are better suited to recover after a fire. As the next two photos show, a silver lining of new growth emerges from the ashes from the 2020 Bush Fire. The Tonto Watershed team routinely monitors riparian areas affected from the 2020 Bush Fire to see the effects of wildlife on the channel’s morphology.

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Figure 5. The state of Cottonwood Creek on October 2020, just a few months after the Bush Fire ravaged the area. USDA Forest Service photo.

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Figure 6. The same location on Cottonwood Creek in July 2021. USDA Forest Service photo.