Analysis of the effects of channel morphometry and network topology on the nonlinearity of hydrologic response as a function of scale.

摘要

Large river basins can be approximated as linear systems (i.e. their output can be considered as a convolution of system's responses to individual space-time rainfall inputs) and the hydrologic response of small catchments is in general non-linear (i.e. affected by flow interactions within the network). This fact has been documented in many empirical studies during the last forty years. However, no satisfactory explanation of the nature of this spatially varying nonlinearity has yet been provided. The overall goal of this study is to understand and quantify the hydrologic response of a basin (and particularly its nonlinear nature) as it varies systematically downstream and to explore the connection of this systematic variation to the variation in channel morphometry (i.e. properties characterizing the shape of the channel cross-section) with contributing area. The study is composed of three major parts:; Incorporating the spatio-temporal distribution of rainfall and basin geomorphology into phase-space based nonlinear prediction of streamfow : In this study we introduce a methodology which incorporates the dynamics of runoff, spatio-temporal structure of rainfall and catchment geomorphology simultaneously into a nonlinear analysis and prediction of streamflow time-series. The proposed framework, based on “hydrologically-relevant” rainfall-runoff phase-space reconstruction is used to study the effect of the complexity of rainfall input on the predictability of streamflow.; A multiscaling formalism for at-station and downstream hydraulic geometry: Based on empirical evidence that the parameters of hydraulic geometry (HG: power laws connecting discharge to stream geometry) vary systematically with contributing area, we postulate and test a lognormal multiscaling model for cross-sectional area and discharge and revise the HG to reflect scale-dependency. Combining the revised hydraulic geometry with geomorphologic analysis of a river network we propose a scheme for runoff routing in ungauged catchments.; On the effect of channel morphometry on hydrologic response: In this study we explore the physical basis for the observed scale-dependence in HG by analyzing the connection between the systematic variations of channel morphometry downstream and the parameters of HG. An important observation relating the downstream variation of channel cross-sectional geometry at bankfull and variability of flood discharges is also discussed in the context of hydrologic response.