Hydrology & Geomorphology
A bottom-up control on fresh-bedrock topography under landscapes
Daniella has been pursuing Zb, the depth to unweathered bedrock, which has been called (by her former advisor, Bill Dietrich) the second most important landscape surface. The depth to unweathered bedrock influences subsurface runoff paths, erosional processes, moisture availability to biota, andwater flux to the atmosphere. Daniella formulated a simple model that predicts the vertical depth weathered rock underlying soil-mantled hillslopes. After uplift and erosion bring fresh bedrock near the Earth’s surface, channel incision (e.g. by Elder Creek at Rivendell) causes water that once saturated spaces in the fresh bedrock to drain to the channel. Drainage of the fresh bedrock allows weathering through drying, setting the upper elevational boundary of undrained fresh bedrock, Zb. The slow drainage of fresh bedrock exerts a “bottom up” control on the advance of the weathering front. The thickness of the weathered zone is calculated as the difference between the predicted topographic surface profile (driven by erosion) and the predicted groundwater profile (driven by drainage of fresh bedrock). Together, these factors control how long rock moisture stored beneath hills can sustain runoff to rivers during drought.
Hydrology of seasonally dry ecosystems
David’s research at Angelo focuses on the hydrology of seasonally dry ecosystems. Seasonally dry ecosystems occur in climatic regions that exhibit distinct periods of high water availability followed by extended intervals during which rainfall is negligible and surface water becomes increasingly scarce. Angelo Coast Range Reserve would be considered seasonally dry due to its Mediterranean seasonality, with cool, wet winters and warm, dry summers. However, seasonally dry ecosystems do not only occur in Mediterranean regions, such as coastal California; they are also found throughout the world’s Savanna and Monsoonal climatic regions. All together, seasonally dry ecosystems constitute over 30% of the planet by area and contain over 30% of the world’s population. David’s main focus in these ecosystems is the seasonal streamflow recession – the long, sustained release of groundwater in the form of streamflow over the course of the dry season. He uses a combination of data analytic and mathematical techniques to model streamflow in seasonally dry ecosystems and to infer watershed properties from the character of seasonal recessions. Ultimately, David hopes to use risk-based mathematical frameworks to measure and predict the impact of growing human populations and a changing wet season climate on the important water resources and unique in-stream ecology found in seasonally dry ecosystems. David is former postdoc with the Eel River Critical Zone Observatory at UC Berkeley, as well as a former Assistant Professor at Sacramento State University. He currently works as a Research Hydrologist for the USDA Forest Service.
Linkages of geology, topography, and trees
Jesse aspires to better understand process linkages between geology, topography, and life. One striking observation from the Eel River watershed is that the regional forest distribution appears to be controlled to first order by lithologic variation across accreted terranes. For example, coniferous forests are rare in the central mélange belt, but the mechanisms inhibiting conifer forests in the mélange are poorly understood. Jesse also seeks to understand how tectonic forcing, biota, and geomorphic processes produce unique landscape form across the different rock types in the area. For example, hillslopes are steep and convex or planar in the greywackes and argillites of the Eel River Critical Zone Observatory. On neighboring mélange, in contrast, landscapes are gently undulating. Processes responsible for hillslope sediment transport (and ultimately landscape form) are not well understood for either rock type. One way to explore a process inferred from field observation is to cast it in the form of a geomorphic transport law, which can be coupled with continuity (conservation of mass) in a model landscape. Resulting simulations can be compared with high resolution (LiDAR) topography from real landscapes to calibrate and test the validity of the proposed transport law. Jesse Hahm is a former PhD student advised by Bill Dietrich in the Earth and Planetary Science Department, University of California, Berkeley. He is now an Assistant Professor in the Dept. of Geography at Simon Fraser University.
Tracing raindrops through trees and bedrock to streams using stable isotopes
Jasper Oshun studies flow paths of precipitation through a forested hillslope to better understand runoff generation and storm flow, the storage of plant-available water in fractured bedrock beneath the soil surface, and the slow release of rock moisture from a hillslope to the stream. Using measurements of the isotopic composition of water, Jasper can trace a raindrop through the hillslope and identify the depth in the rock beneath from which trees derive their water. Thus far, he has shown that the isotopic composition of water within a hillslope varies as a function of how tightly it is held within the pores of soil and weathered rock. This variability persists throughout the year and is an identifiable ‘blueprint’ from which the above vegetation draws its water. Surprisingly, different species of trees have different water use strategies, which results in adjacent trees partitioning water from the soil, and weathered rock. Species-specific water use by trees on the hillslope may thus affect the amount of water stored in rock, and the slow release of water to our streams. These findings can inform forest management strategies that seek to maximize water yield from our forests. Jasper Oshun is a former Ph.D. student with Bill Dietrich in the Department of Earth and Planetary Science at UCB. He is now an Assistant Professor at Humboldt State University.