Temporal river channel changes in the Gila Box Riparian National Conservation Area, Arizona, USA
Human activities have led to the serious decline and degradation of riparian areas in the Southwestern United States. Areas in Arizona, such as the Gila Box Riparian National Conservation Area, are protected to conserve and restore these unique ecosystems. This study investigated temporal change in the channel form and sinuosity of the Gila River in the Gila Box Riparian National Conservation Area. Specifically, cross sections were measured in 1994, 2001, and 2008 to evaluate changes in channel form. Aerial photographs between 1935 and 2007 were also compared to assess changes in channel sinuosity. Based on cross-sectional measurements, the thalweg was significantly deeper in 1994 than in 2001 and 2008, while width-depth ratios were significantly lower in 2008 than in 1994 and 2001. These measurements indicate that the channel is stabilizing. Sinuosity changed only slightly. Overall, climate patterns that cause large flood events appear to have been the major influence on the channel form. Still, exclusion of livestock and all-terrain vehicles, which increased vegetation in the riparian areas, also appeared to mitigate flood impacts. The stream channel appears to have been more resilient to the impacts of the flood in 2005, when vegetation was better established, than to the flood of 1993, when past management influences were still lingering.
- Case ID: INT-073-1
- Intervention type: Protection
- Intervention description:
The Gila Box encompasses 9300 ha, with 65 km of river. Since 1990, the BLM has excluded vehicle use, livestock grazing, sand and gravel excavation, and oil and gas exploration. Recreation is now the primary use of the Gila Box.
The management goals are to conserve, protect, and enhance its riparian areas [of desert biomes in SW USA], associated resources, and the aquatic, wildlife, archeological, paleontological, scientific, cultural, recreational, educational, scenic and other resources and values of such areas (USDIBLM, 1998).
- Landscape/sea scape ecosystem management:
|Climate change impacts
||Effect of Nbs on CCI
||changes in river sinuosity (aerial imagery); Sinuosity is the ratio of stream length to valley length
changes in channel morphology (channel/bank elevation; thalweg depth; width-depth ratio)
Authors then looked at how these changes in relation to when large floods (peak streamflow measures) occurred, and how in turn this coincides with the timing of the intervention
- Approach implemented in the field:
- Specific location:
The Gila Box Riparian National Conservation Area.
It has four perennial waterways, the Gila and San Francisco rivers and Bonita and
- Country: United States of America
- Habitat/Biome type: Deserts and xeric shrublands |
Streams, rivers, riparian |
- Issue specific term: Not applicable
- Notes on intervention effectivness: Observed outcome is - The width-depth ratio and thalweg depth comparisons among the survey years indicate that the stream channel is stabilizing.
Authors investigate changes that have occurred over time in the stream channel form of the Gila River in the Gila Box since its establishment as a conservation area. Authors then looked at how these changes in relation to when large floods (peak streamflow measures) occurred, and how in turn this coincides with the timing of the intervention. “If any differences were found, they were expected to be correlated with hydrologic events (e.g., major flood events), erosion and deposition cycles, and/or management changes (i.e., exclusion of cattle and ATVs) that occurred during these periods of time.’ “In the Gila Box, livestock and off-road vehicle use were excluded in the early 1990s. The stability of the stream channel during the 2005 flood can be attributed to the increase in riparian vegetation resulting from management practices within the Gila Box. This was not evident in 1993, probably because the exclusions had recently been established.”
The removal of livestock and the exclusion of ATVs and other anthropogenic disturbances, which we have observed over time to increase riparian vegetation, also probably mitigated the impact of the 2005 flood.
“Climate appears to be the dominant factor, but simple human management action, for example the exclusion of livestock and ATVs, can help protect and conserve rare ecosystems such as the Gila Box Riparian National Conservation Area.”
- Is the assessment original?: Yes
- Broadtype of intervention considered:
- Compare effectivness?: No
- Compared to the non-NBS approach:
- Report greenhouse gas mitigation?: No
- Impacts on GHG:
- Assess outcomes of the intervention on natural ecosystems: No
- Impacts for the ecosystem:
- Ecosystem measures:
- Assess outcomes of the intervention on people: No
- Impacts for people:
- People measures:
- Considers economic costs: No
- Economic appraisal conducted: No
- Economic appraisal described:
- Economic costs of alternative considered: No
- Compared to an alternative:
- Type of data:
- Is it experimental: No
- Experimental evalution done:
- Non-experimental evalution done:
Empirical case study
- Study is systematic: