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Accueil du site → Doctorat → États-Unis → 2017 → Factors affecting the streamflow and in-stream nitrate concentration in semi-arid areas : sub-surface flow-generation, vertical distribution of soil nitrate and drainage properties, and the connectivity of impervious areas

University of California, Santa Barbara (2017)

Factors affecting the streamflow and in-stream nitrate concentration in semi-arid areas : sub-surface flow-generation, vertical distribution of soil nitrate and drainage properties, and the connectivity of impervious areas

Chen, Xiaoli

Titre : Factors affecting the streamflow and in-stream nitrate concentration in semi-arid areas : sub-surface flow-generation, vertical distribution of soil nitrate and drainage properties, and the connectivity of impervious areas

Auteur : Chen, Xiaoli

Université de soutenance : University of California, Santa Barbara

Grade : Doctor of Philosophy (PhD) 2017

Résumé
The Southern California coastal region is one of the five areas in the world with Mediterranean climate. The long dry summer and cool wet winter not only attract a large population, but also create a unique hydrologic signature with strong temporal and spatial heterogeneity in soil moisture, streamflow and vegetation water use.. The sandy soil, fractured and uplifting bedrocks in undeveloped areas result in flashy and non-linear hydrologic responses to storms. Urbanization in this area further alters the hydrograph by changing the land cover and drainage patterns . These changes alter both water and nitrate fluxes, which may have substantial impacts on the downstream and coastal ecosystems, such as Great Kelp forest in the Santa Barbara channel. To understand and ultimately manage of water resources in this region must take these multiple factors climate, soil and urbanization into account. Study and modeling of flow generation and nitrate transport mechanisms in the undeveloped area, and disturbance of nitrate cycling and nitrate export in the urban areas in this region may reveal new insight and improve the understanding of hydrologic processes, and provide sustainable watershed management strategies. Southern California coastal mountain watersheds are characterized by a Mediter ranean climate, sandy soil, shallow rock, flashy hydrologic responses and drought tolerant vegetation such as oak and chaparral [51, 93]. The geological condition in this area may fit vii the requirement condition of ’Fill & Spill’ hypothesis of subsurface flow generation mech anism. We adapted ’Fill & Spill’ submodel in an eco-hydrologic model, Regional Hydro Ecologic Simulation system (RHESSys) [23], implemented it in the semi-arid area, and compare its model performance with the traditional ’Continuous Transmissivity’ model which assume the soil hydraulic conductivity follows a continuous exponential function [3]. Our results show that in the recession period, the modeled discharge from ’Fill & Spill’ model dropped much faster than the one from ’Continuous Transmissivity’ model, and fit the observed discharge data better. ’Fill & Spill’ model is also less sensitive to small precipitation events, and tends to increased estimates of peak flow. Assessment of whether peak flow responses by the ’Fill & Spill’ model are a better representation of observed dynamics is challenging given that peak flow observed data is prone to un certainties from di↵erent sources such as heterogeneity in precipitation distribution and errors in stream gauge stations, and may not reflect the true hydrologic response of wa tershed behavior. In summary, model assessments show that the ’Fill & Spill’ model results in substantially di↵erent recession behavior and that, for the study watershed, the ’Fill & Spill’ model may be a better predictor of the watershed hydrologic responses to precipitation events better than ’Continuous Transmissivity’ model.

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Page publiée le 2 octobre 2017