Distributed Watershed Model Research Articles

Sensitivity and uncertainty analysis coupled with automatic calibration for a distributed watershed model

Distributed watershed models should pass through a careful calibration procedure before they are utilized as a decision making aid in the planning and management of water resources. Although manual approaches are still frequently used for calibration, they are tedious, time consuming, and require experienced personnel. This paper describes an automatic approach for calibrating daily streamflow and daily sediment concentration values estimated by the US Department of Agriculture's distributed watershed simulation model, Soil and Water Assessment Tool (SWAT). The automatic calibration methodology applies a hierarchy of three techniques, namely screening, parameterization, and parameter sensitivity analysis, at the parameter identification stage of model calibration. The global parameter sensitivity analysis is conducted using a stepwise regression analysis on rank-transformed input–output data pairs. Latin hypercube sampling is used to generate input data from the assigned distributions and ranges, and parameter estimation is performed using genetic algorithm. The Generalized Likelihood Uncertainty Estimation methodology is subsequently implemented to investigate uncertainty of model estimates, accounting for errors due to model structure, input data and model parameters. To demonstrate their effectiveness, the parameter identification, parameter estimation, model verification, and uncertainty analysis techniques are applied to a watershed located in southern Illinois.

Assessment and modelling of the influence of man-made networks on the hydrology of a small watershed: implications for fast flow components, water quality and landscape management

Up to now, most watershed models have been focused on the representation of ‘natural’ flow and transport processes. In this paper, we discuss the role of man-made networks, such as ditches, roads, hedge rows and hedges, underground drainage by buried pipes, etc. The influence of such features on the hydrology of a watershed may be of particular importance if the aim of the modelling is to predict the effect of landscape management or the fate of contaminants, e.g. pesticides, when a rain event occurs very soon after their spreading on the soil surface. It is likely that such artificial networks may act as conduits or short-circuits for the transport of contaminants, either dissolved or sorbed on soil particles, by-passing some of the retardation mechanisms such as sorption in the soil, retention of surface runoff by grass verges, biodegradation in the unsaturated zone, etc. We first present a small watershed on which the study was conducted, the Kervidy, which is a 5 km 2 ‘bocage 2 2 Bocage is a landscape with grassland, hedges, and occasional trees—often apple trees—typical of Brittany and Normandy. ’ catchment in Brittany, France. The man-made networks were observed and their extent and functioning described. We then included the potential hydraulic role of these networks in a distributed watershed model (TOPOG, [J. Hydrol. 150 (1993) 665]). This modified model, ANTHROPOG, was run, for comparison, with and without the man-made network; sensitivity tests were also made to assess the hydrologic importance of these networks. It was shown that they can have a very significant effect on the functioning of a watershed. We conclude on the relevance of the improved distributed model for the management of rural landscapes, and on the type of additional data needed to calibrate the model with parameters representative of the true processes.

Increasing vulnerability to extreme floods and societal needs of hydrological forecasting

Recent climatic variability seems to be intensifying the hydrological extremes resulting in devastating hydrological hazards, especially floods all over the world, including the arid regions. Disasters are always more tragic in poor countries than in rich ones, as more poor people seem to suffer and die, and the economic losses have a greater impact. On the other hand, in advanced countries, although flood control can reduce the number of deaths, it cannot always reduce economic losses despite the large public investments that have long been applied. This is due to the ever increasing damage potential in a basin where reliance on safety has been created by flood control measures. It is proven that proper prediction and preparedness are the only practical means that can be relied upon to reduce the death toll and economic losses. In a time of climatic variation, physically-based distributed models are to be pursued to obtain reasonable predictions, since the climate is non-stationary and both basin land use and water use are constantly changing. The proper integration of a distributed watershed model with atmospheric circulation models, four-dimensional data assimilation and mesoscale hydrometeorological nested models is the direction for hydrologists to be heading.

並列多目的遺伝的アルゴリズムによる分布型水循環モデルパラメータの最適化

国分寺試験流域における水循環解析に筆者らが用いてきた分布型モデルに含まれる20個のパラメータの自動最適化を試みた.このモデルは,流出量のみならず,流域内の6つの観測井における地下水位も出力するので,そのパラメータ最適化に際しては,多目的最適化の手法を用いる必要がある.また,パラメータ数・流域離散化領域数の増加に応じて増大する計算負荷に対処するために最適化処理の並列化が有効であると考えられる.そこで,大域的探索能力を持ち.並列処理にも対応しやすい多目的遺伝的アルゴリズムを用いてパラメータの最適化をおこなうことにした.あらかじめ各パラメータの値を適当に設定して生成した仮想観測データを用いてGAの諸設定を調整した後,国分寺試験流域の実測データを用いて並列多目的最適化を実行した結果,その有効性を示すことができた.

VERIFICATION AND APPLICATION OF REGIONAL EQUATIONS FOR THE STORAGE FUNCTION RUNOFF MODEL1

ABSTRACTThe storage function model is a nonlinear rainfall‐runoff model that has been developed for and applied to flood runoff analysis in Japan. This paper extends the model applicability by developing practical equations for estimating model parameters which are appropriate on a regional basis, i.e., so‐called regional equations. Previously, the parameters were computed from historical data for a specific basin or from relationships that do not account for land use and topography.To develop the regionalized equations, model parameters were identified for 91 flood events from 22 watersheds in Japan by applying a mathematical optimization technique. Results from 39 of these events were statistically compared and regional relationships were determined as a function of land use, basin area and rainfall intensity. The utility of the estimated equations were tested by computing runoff hydrographs for lumped basins. The estimated parameters were also applied in a distributed watershed model formulation. Both applications showed acceptable results that validate the use of the regionalized relationships.

Application of GIS in Watershed Management

This chapter presents a method to integrate a distributed watershed model with Geographic Information System (GIS) for management of soil erosion and fluvial s…

A DISTRIBUTED DYNAMIC WATERSHED MODEL1

ABSTRACT:A distributed watershed model was developed to mathematically simulate overland and channel flow for a single‐event storm. The modeled watersheds in the study were subdivided into rectangular grid elements. All hydrologically significant parameters, such as land slope, rainfall and precipitation excess, were assumed to be uniform within each element. The Green‐Ampt method was adopted to generate precipitation excess for each element during the simulation period. A two‐dimensional diffusion wave model was used for overland flow routing and an iterative Alternative Direction Implicit scheme was used to solve the simultaneous overland flow equations. Once the overland flow became inflow to the channel, a one‐dimensional dynamic wave flood routing technique, based on a four‐point, implicit, non‐linear finite difference solution of the St. Venant equation of unsteady flow, was applied. A limited number of comparisons were made between simulated and observed hydrographs for areas of about one square mile. Given the appropriate parameters, the model was able to accurately simulate runoff for single‐event storms. This paper describes a distributed watershed model developed to simulate overland and channel flow. Comparisons were made between simulated and observed hydrographs for three watersheds. The model was able to accurately simulate the runoff for single‐event storms using 61‐m by 61‐m (200 ft by 200 ft) watershed grid elements.