Flood risk is directly related to the Rio Chama’s channel capacity. The Chama’s channel is currently victim to a detrimental sediment feedback loop caused by the Abiquiu dam’s mitigation of flood flows and a continued introduction of large sediment loads via tributary convergences below Abiquiu dam. The loss of flood flows also means the loss of natural geomorphic and flood tendencies. The Chama’s flow capacity if currently 1800 cfs due to the acequias and their diversion structures fragility. The energy of the Chama is not high enough to move the large sand and gravel brought to the river via tributaries during monsoon season and large rain events, thus they get deposited and overtime the channel capacity decreases. As the channel’s capacity diminishes, flood risk increases, the paradox of this reach is that flood flows are necessary to halt this feedback loop but as the channel and the floodplain exist today high flows would pose too high a risk to the communities, acequias, homes, and other structures present.
Climate Change
With temperatures predicting to rise and add a few additional degrees by the end of the 21st century, it has the potential to cause significant environmental harm and change the hydrology of the region (US Department of Interior 2013). It has been proven that changes will be seen in the magnitude, timing and variability of inflows to the system. These changes coupled with the temperature increases will cause significant changes in the available water supply and demand. This may translate to less water in reservoirs as a higher demand is coming from downstream users. With less water in the reservoirs it is likely to reduce the amount of hydropower generation coming from the Upper Rio Grande system With less water running through the system, no matter at what time of the year, it will begin to introduce changes to the system downstream as the environmental flows will be more of a challenge to maintain. Such events might include a higher deposition of sediments as there is a loss of the higher flows to flush the channel. With less water there will be a loss of overbank flooding which induces challenges to riparian recruitment, bank stabilization, loss of habitat, endangerment of species and endangerment to the surrounding communities. The flood plains will begin to move further instream as a result of channel incision. With a low discharge coming down stream as well as a loss of stream width, acequias will have to begin to consider ways to get water into their channels to survive. Solutions will need to be implemented into the community such as consolidation of structures or channel restructuring as a way to introduce water back to the land. Without the water reaching the acequias, agricultural services may be lost.
Although projections of annual precipitation are uncertain, precipitation in spring, already the dry season in New Mexico, is projected to decrease across most of the state (Frankson, et. al., 2017). Shortages during peak agricultural seasons will reduce crop production and increase the price of water. The centuries-old water-sharing system in place through mayordomo governance of the acequias may be in jeopardy as water brokers fight for a share of the river ( Rivera, J.A. 1996). This may lead to a very important potential for climate change to affect the upstream and downstream users as to disrupt the allocation and management of the upper Rio Grande's water resources as well. Physical changes to the system have already been happening. To make it apparent the drier the land will ultimately reduce channel capacity, meaning that lower flows will cause flooding. Additionally, lower flows reduce the capacity of the river to absorb and dilute pollutants, worsening water quality. Due to the increased temperature and vegetation cover forest fires are to be watched. Along with this comes the possibility of maintaining the water quality to become more difficult. The dry temperatures will increase the evaporation leaving the soil dryer which can also prompt forest fires. Forest fires usually produce a flash flood, washing ash and other harmful pollutants into the water such as; nitrogen, phosphorous, suspended solids, and salt. Climate change and lower over- all stream flows might also lead to additional reaches falling below water quality standards, and therefore to pollution controls and higher costs (Hurd, B., & Coonrod, J. 2012). The effects of increased flooding hazards are becoming increasingly apparent. Climatic changes will begin to change the frequency and intensity of summer monsoonal storms which may lead to property or acequia damages in the area. Some evidence suggests that summer precipitation associated with monsoonal flow and thunderstorm activity could increase across south- west USA and in the Rio Grande basin, in particular (Nohara D, Kitoh A, Hosaka M, Oki T 2006). Because of the increase in flood damage potential coupled with lower flood plains and degradation of levee support, homes could be in danger. Climate change is apparent and is happening all over the world, the best way to be prepared and safe is to be informed about what is happening around.
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