Continuous Hydrological Simulations with the NCUDWM Distributed Watershed Model
Abstract
The object of this study is to investigate the responses with which temporal resolutions of rainfall inputs shape the character of continuous hydrological simulations of distributed watershed models. A fully distributed watershed model, NCUDWM, has been developed for resolving watershed hydrological responses in a variety of spatial and temporal scales. The model interactively coupled three modules of 1-D river flow, 2-D surface runoff, and 3-D variable-saturated subsurface flow. The river flow is simulated by the 1-D diffusive wave approach for each river segment with the conservation of mass and the continuity of stage for river junctions. The surface runoff is simulated by the 2-D diffusive wave approach and eight flow directions are allowed for runoff in/out of each surface grid. The interactions between river flow and surface runoff is determined by the continuity of stage and the conservation of mass when water of two regimes are connected and stage differences exist. Daily evapotranspiration is estimated by multiplying the potential evapotranspiration, either prescribed or computed, by the crop coefficient determined from land use. The subsurface flow is a quasi 3-D approach, including soil moisture movements in the vertical direction and groundwater flows in the horizontal direction described by the Darcy’s law. The interactions between subsurface water and surface water (river and surface runoff) is described by the direct connection approach that flux and head continuities are conserved. This study examines hourly and daily flow simulations by NCUDWM with observed daily precipitations embedded with hourly precipitations for extreme events. The study site is the Shihmen Reservoir watershed (catchment area: 736 km2; elevations: 135-3529 m) in northern Taiwan and a yearly long simulation was performed for 2001. The first run was performed by merely providing daily precipitations in 2001. The second run was conducted by considering hourly precipitations of three typhoons making landfalls in Sept.-Oct. which account for more than 40% of annual precipitation. Preliminary results show that: (a) discrepancies of total runoff depths between two runs, for both yearly scale and discrete extreme events, are not significant as performed by the NCUDWM; (b) the first run is unable to resolve peak flows and peak discharge time down to hourly scale as a result of lacking finer temporal resolutions of rainfall input; and (c) in view of capturing daily discharges in continuous simulations as performed by the NCUDWM, hourly resolution of rainfall input is optional.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.H11E0850S
- Keywords:
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- 1805 HYDROLOGY / Computational hydrology;
- 1816 HYDROLOGY / Estimation and forecasting;
- 1817 HYDROLOGY / Extreme events;
- 1879 HYDROLOGY / Watershed