System dynamics model for predicting floods from snowmelt in North American prairie watersheds

This study uses a system dynamics approach to explore hydrological processes in the geographic locations where the main contribution to flooding is coming from the snowmelt. Temperature is identified as a critical factor that affects watershed hydrological processes. Based on the dynamic processes of the hydrologic cycle occurring in a watershed, the feedback relationships linking the watershed structure, as well as the climate factors, to the streamflow generation were identified prior to the development of a system dynamics model. The model is used to simulate flood patterns generated by snowmelt under temperature change in the spring. Model structure captures a vertical water balance using five tanks representing snow, interception, surface, subsurface and groundwater storage. Calibration and verification results show that temperature change and snowmelt play a key role in flood generation. Results indicate that simulated values match observed data very well. The goodness‐of‐fit between simulated and observed peak flow data is measured using coefficient of efficiency, coefficient of determination and square of the residual mass curve coefficient. For the Assiniboine River all three measures were in the interval between 0·92 and 0·96 and for the Red River between 0·89 and 0·97. The model is capable of capturing the essential dynamics of streamflow formation. Model input requires a set of initial values for all state variables and the time series of daily temperature and precipitation information. Data from the Red River Basin, shared by Canada and the USA, are used in the model development and testing. Copyright © 2002 John Wiley & Sons, Ltd.     

Remote sensing observations of biological material by LANDSAT along a tidal thermal front and their relevancy to the available field data

Two images recorded on two successive summer days by LANDSAT satellite over the western approaches to the English Channel show bright pattern of complex shape the origin of which is puzzling. Among the wavelength bands available on LANDSAT's multispectral scanner, these patterns are apparent only in the green region of the spectrum, and they are located towards the stratified side of a well marked tidal thermal front. Spectral signature analysis and available knowledge on hydrography and plankton in the area are used to derive a proposed interpretation. Phytoplankton would accordingly be the best candidate for being responsible for the observed patterns.     

The impact of parameter lumping and geometric simplification in modelling runoff and erosion in the shrublands of southeast Arizona

There have been many studies of hydrologic processes and scale. However, some researchers have found that predictions from hydrologic models may not be improved by attempting to incorporate the understanding of these processes into hydrologic models. This paper quantifies the effect of simplifying watershed geometry and averaging the parameter values on simulations generated using the KINEROS2 model. Furthermore, it examines how these changes in model input effect model output. The model was applied on a small semiarid rangeland watershed in which runoff is generated by the infiltration excess mechanism. The study concludes that averaging input parameter values has little effect on runoff volume and peak in simulating runoff. However, geometric simplification does have an effect on runoff peak and volume, but it is not statistically significant. In contrast, both averaging input parameter values and geometric simplification have an effect on model‐predicted sediment yield. Copyright © 2005 John Wiley & Sons, Ltd.     

具有Horton及Dunne机制的径流模型在VIC模型中的应用(英)

地表径流主要由蓄满(Dunne)和超渗产流(Horton)机制产生;土壤性质的空间变异性、前期土壤水、地形及降水的空间变异性导致不同的径流机制。在研究区域或模型网格内,蓄满产流及超渗产流可能同时出现,缺乏考虑任何一种机制以及土壤性质的次网格空间变率可能导致地表径流的过高或过低估计,从而影响土壤水的计算。利用Philip入渗公式用于时间压缩逼近(TCA)给出了一种径流参数化方法,该方法可以动态实现模型网格中的Horton及Dunne产流机理,它考虑了土壤空间变异性对Horton和Dunne径流的影响。该径流模型应用到基于水文原理的陆面过程模型VIC,在淮河流域及美国宾西法尼亚州的一个流域进行了测试,结果表明:新的参数化方法对地表径流和土壤水分含量的分配起着重要作用,对于改进径流和土壤水的模拟有重要意义。     

全新世以来华北平原层圈间水循环演化过程与区域地下水演变周期性

该文阐述全新世以来大气圈、岩石圈、生物圈与水圈之间水文循环过程中水分通量的演化规律,揭示了近百年来人类活动对层圈之间水分通量变化的干扰作用,并依据全新世时期千年尺度和百年尺度水文循环演化的特点,分析和预测了华北平原区域地下水演变的周期性和未来30~50 a趋势.     

Saturated area dynamics and streamflow generation from coupled surface–subsurface simulations and field observations

A distributed physically-based model describing coupled surface–subsurface flows is applied to an instrumented catchment to investigate the links between runoff generation processes and the dynamics of saturated areas. The spatial characterization of the system is obtained through geophysical measurements and in situ observations. The model is able to reproduce the dynamics of the system through the calibration of only few parameters with a clear physical interpretation, providing a solid basis for our numerical investigations. Such investigations demonstrate the important control exerted by surface topography on the time evolution of saturated area patterns, mainly mediated by topographic curvature, that dictates both the dominant streamflow generation process at the local scale and the connection-disconnection dynamics of saturated areas. The relation between hillslope water storage and streamflow, Q = f(V), is shown to be highly hysteretical and dependent on the mean saturation of the catchment: higher degrees of saturation tend to yield one-to-one relationships between streamflow and water storage. On the contrary, streamflow-water storage relations are importantly affected by the specific configuration of saturated areas connected to the outlet when the system is far from complete saturation. This observation contradicts common assumptions of a one-to-one relationship Q = f(V) often used to justify widely observed power-law Q vs. dQ/dt recession curves. Furthermore, even when Q = f(V) becomes unique at high degrees of saturation, no power-law form emerged in our runs, speculatively because of the small size of the catchment formed by a single incision and the corresponding hillslope.     

青藏高原水系特征遥感影像解译方法研究

我国西部地区1∶50000地形图的缺失,制约了该区域经济建设和社会发展,给我国西部大开发战略的实施带来了困难。影像解译是整个测绘工程中的关键环节之一,水系特征又是各类地物中的关键要素。本文通过对不同影像中青藏高原水系特征的解译,结合其它技术手段,综合运用各类信息,在此基础上提出了针对不同水系特征的解译提取方法。结果表明,针对不同水系特征的特点,利用不同的遥感数据源,结合其它技术手段,加上各类信息的运用,能够有效地提取青藏高原的各类水系特征,基本能够满足1∶50000地形图的测绘需求。     

CryoSheds: a GIS modeling framework for delineating land-ice watersheds for the Greenland Ice Sheet

Choice of watershed delineation technique is an important source of uncertainty for cryo-hydrologic studies of the Greenland Ice Sheet (GrIS), with different methods yielding different watersheds for a common pour point. First, this paper explores this uncertainty for the Akuliarusiarsuup Kuua River Northern Tributary, Western Greenland. Next, a standardized, semi-automated modeling framework for generating land-ice watersheds for GrIS land-terminating ice (henceforth referred to as CryoSheds) using geographic information systems (GIS) hydrologic modeling tools is presented. The framework uses ArcGIS and the ArcPy geoprocessing library to delineate two types of land-ice watersheds, namely those defined by: (1) a hydraulic pressure potential with varying water to ice overburden pressure ratios (k-value), which determines theoretical flow paths from the hydrostatic equation, using surface and bedrock digital elevation models (DEMs) and (2) a surface topography DEM alone. Lastly, a demonstration of the CryoSheds method is presented for seven remotely sensed proglacial pour points along the Aussivigssuit River (AR), Western Greenland, and its largest tributaries. GrIS meltwater runoff from these seven nested land-ice watersheds is estimated using Modele Atmospherique Regional (MAR) v.3.2 and runoff uncertainties due to watershed delineation parameter selection is estimated.     

UNSTEADY MOVEMENT OF FRESH WATER IN THICK UNCONFINED SALINE AQUIFERS

Abstract

Fresh-water lenses are formed in unconfined saline aquifers in response to deep percolation from rainfall, artificial recharge, and seepage from irrigation waters and/or in response to injecting fresh water through vertical or horizontal wells. An approximate differential equation is derived in terms of the depth of the fresh-salt water interface below the initial position of the saline-water table. This equation is analogous to that of the ground-water motion in two dimensions. The wealth of knowledge available from solving the latter equation is used to obtain approximate expressions for the movement of the fresh-salt water interface in several flow systems wherein this interface does not reach the bottom of the aquifer. These approximate solutions as well as others for related quantities of interest may afford useful tools for rationally planning the extraction of usable waters from such flow systems.     

Fifty years of runoff response to conversion of old-growth forest to planted forest in the H. J. Andrews Forest,Oregon, USA

Long-term watershed experiments provide the opportunity to understand forest hydrology responses to past logging, road construction, forest regrowth, and their interactions with climate and geomorphic processes such as road-related landslides. We examined a 50-year record from paired-watershed experiments in the H. J. Andrews Experimental Forest, Oregon, USA in which 125 to 450-year-old conifer forests were harvested in the 1960s and 1970s and converted to planted conifer forests. We evaluated how quickflow and delayed flow for 1222 events in treated and reference watersheds changed by season after clearcutting and road construction, including 50 years of growth of planted forest, major floods, and multi-decade reductions in snowpack. Quickflow runoff early in the water year (fall) increased by up to +99% in the first decade, declining to below pre-harvest levels (−1% to −15%) by the third to fifth decade after clearcutting. Fall delayed flow responded more dramatically than quickflow and fell below pre-treatment levels in all watersheds by the fifth decade, consistent with increased transpiration in the planted forests. Quickflow increased less (+12% to 70%) during the winter and spring but remained higher than pre-treatment levels throughout the fourth or fifth decade, potentially impacted by post-harvest burning, roads, and landslides. Quickflow remained high throughout the 50-year period of study, and much higher than delayed flow in the last two decades in a watershed in which road-related changes in flow routing and debris flows after the flood of record increased network connectivity. A long-term decline in regional snowpack was not clearly associated with responses of treated vs. reference watersheds. Hydrologic processes altered by harvest of old-growth conifer forest more than 50 years ago (transpiration, interception, snowmelt, and flow routing) continued to modify streamflow, with no clear evidence of hydrologic recovery. These findings underscore the importance of continued long-term watershed experiments.