Chiricahua Mountains - Reduction of Channel Gradients

Science Center Objects

Drainages in the Chiricahua Mountains are impacted by large rain events that cause gullying effects in the headwaters, overflow at road crossings, flooding of campgrounds, and overwhelming sediment loads at outlets (Chiricahua National Monument). Monsoon rains following recent fires cause severe flooding in most drainages and debris flows in many others (Youberg et al. 2013). Watershed restoration has been a major goal of private land owners at the El Coronado (EC) ranch.

Drainages in the Chiricahua Mountains are impacted by large rain events that cause gullying effects in the headwaters, overflow at road crossings, flooding of campgrounds, and overwhelming sediment loads at outlets (Chiricahua National Monument). Monsoon rains following recent fires cause severe flooding in most drainages and debris flows in many others (Youberg et al. 2013). Watershed restoration has been a major goal of private land owners at the El Coronado (EC) ranch.

Map of paired watersheds

Figure 1. Map of paired watersheds

(Public domain.)

Measuring Stream Discharge

  • The treated watershed has a lower runoff response and reduced peak flows.
  • The rock detention structures reduce the average rate of flow by more than half.
  • The treated watershed has ~28% more flow volume than the untreated watershed.
  • Management using check dams can extend summer base-flow in arid lands.

We used the Soil and Water Assessment Tool (SWAT) to model the paired watersheds and develop future scenarios to consider longer-term impacts to the water budget and future scenarios. SWAT has been used for studying the impact of land use change and climate change as well as their combined/interactive effect on water resources (Arnold et al. 1998). Model outputs are estimates of the local water budget (storage, streamflow, runoff, infiltration, interception, and evapotranspiration).

Photo of streams converging where treated watershed has less sediment.

Figure 2. Photo of streams converging where treated watershed has less sediment.

(Public domain.)

Modeling Discharge & Sediment

We used the Soil and Water Assessment Tool (SWAT) to model the paired watersheds and develop future scenarios to consider longer-term impacts to the water budget and future scenarios. SWAT has been used for studying the impact of land use change and climate change as well as their combined/interactive effect on water resources (Arnold et al. 1998). Model outputs are estimates of the local water budget (storage, streamflow, runoff, infiltration, interception, and evapotranspiration).

  • Using the Soil and Water Assessment Tool (SWAT), calibrated for streamflow using discharge from 2013 at a Control site (PBIAS = +/- 2.34%), we examined the impacts of check dams at a watershed Treated with check dams.
  • Precipitation event >= 15mm to instigate the erosion (2% occurrence).
  • ~ 630 tons of sediment predicted to be stored behind check dams in the Treated watershed over the 3-year simulation. 
  • Resulting watershed model useful as predictive framework & decision-support tool to consider long-term impacts of restoration and potential for future restoration.
Output of SWAT model displaying sediment yield events.

Figure 3. Output of SWAT model displaying sediment yield events.

(Public domain.)

Analyzing Sediment Chemistry **Carbon**

  • Sampled Stable isotope ratios of carbon and nitrogen (δ 13C and δ 15N)
  • ECS have the potential to reduce carbon losses from watersheds based on fire severity “carbon rescue”
  • Results of this study were scaled-up to estimate the impact on carbon storage if ECS were installed in the forest ecosystems of the southwestern United States  (0.019 petagrams)

Works Cited

Arnold, J. G., Srinivasan, R., Muttiah, R. S., & Williams, J. R. (1998). Large Area Hydrologic Modeling and Assessment Part I: Model Development1. JAWRA Journal of the American Water Resources Association34(1), 73–89. doi:10.1111/j.1752-1688.1998.tb05961.x

Smith, C.F., Cordova, J.T., and Wiele, S.M., 2010, The continuous slope-area method for computing event hydrographs: U.S. Geological Survey Scientific Investigations Report 2010–5241, 37 p.

Waidler, D., White, M., Steglich, E., Wang, S., Williams, J., Jones, C. A., & Srinivasan, R. (2011). Conservation practice modeling guide for SWAT and APEX. Texas Water Resources Institute Technical Report, (399), 71.

Youberg, Ann; Neary, Daniel G.; Koestner, Karen A.; Koestner, Peter E. 2013. Post-wildfire erosion in the Chiricahua Mountains. In: Gottfried, Gerald J.; Ffolliott, Peter F.; Gebow, Brooke S.; Eskew, Lane G.; Collins, Loa C. Merging science and management in a rapidly changing world: Biodiversity and management of the Madrean Archipelago III and 7th Conference on Research and Resource Management in the Southwestern Deserts; 2012 May 1-5; Tucson, AZ. Proceedings. RMRS-P-67. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 357-361