Waimea Canyon is a deep V-shaped canyon on the island of Kauai, Hawaii in which the Waimea River and its tributaries flow. The shape and size of the canyon are noteworthy and unusual compared to its contemporary canyons on the Hawaiian Islands which are usually U-shaped or flat bottomed. This could be because there is significantly more physical erosion in Waimea Canyon compared to others. A water budget was created using ArcGIS Pro and data from the University of Hawaii’s rainfall and evapotranspiration atlases, as well as from the United States Geological Survey’s stream gage data. A mass flux was estimated using ArcGIS pro by creating a paleosurface from the ridge points and then finding the mass difference between todays watershed and the watershed with the paleosurface. Weathering reactions were made to model the processes in the watershed. The reactants were found from using oxide percentages of Kauai basalts and inputting them into MELTs to estimate mineralogy. The products were found by analysis of soil and water samples in the area of the Canyon. In the Waimea River watershed approximately 159 t/km2 /yr is removed, of which 56% is by physical erosion. This was compared to the V-shaped Makaweli river watershed where approximately 12% is removed by physical erosion and in the U-shaped Hanalei watershed ≈ 68% is removed. While these differences could be explained by vegetation cover, precipitation, and slope steepness it shows that there is not more physical erosion in Waimea Canyon compared to the others. Thus, the origin of the V-shape of Waimea Canyon remains unexplained.

Considerable interest lies in understanding the hydrologic response to climate change in the upper Deschutes Basin, particularly as it relates to groundwater fed streams. Much of the precipitation occurring in the recharge zone falls as snow. Consequently, the timing of runoff and recharge depend on accumulation and melting of the snowpack. Numerical modeling can provide insights into evolving hydrologic system response for resource management consideration. A daily mass and energy balance model known as the Deep Percolation Model (DPM) was developed for the basin in the 1990s. This model uses spatially distributed data and is driven with daily climate data to calculate both daily and monthly mass and energy balance for the major components of the hydrologic budget across the basin. Previously historical daily climate data from weather stations in the basin was used to drive the model. Now we use the University of Washington Climate Impact Group's 1/16th degree daily downscaled climate data to drive the DPM for forecasting until the end of the 21st century. The downscaled climate data is comprised from the mean of eight GCM simulations well suited to the Pacific Northwest. Furthermore, there are low emission and high emission scenarios associated with each ensemble member leading to two distinct means. For the entire basin progressing into the 21st century, output from the DPM using both emission scenarios as a forcing show changes in the timing of runoff and recharge as well as significant reductions in snowpack. Although the DPM calculated amounts of recharge and runoff varies between the emission scenario of the ensemble under consideration, all model output shows loss of the spring snowmelt runoff / recharge peak as time progresses. The response of the groundwater system to changing in the time and amount of recharge varies spatially. Short flow paths in the upper part of the basin are potentially more sensitive to the change in seasonality. However, geologic controls on the system cause this signal to attenuate as it propagates into the lower portions of the basin. This scale-dependent variation to the response of the groundwater system to changes in seasonality and magnitude of recharge is explored by applying DPM calculated recharge to an existing regional groundwater flow model.