Design hydrograph estimation in small and ungauged watersheds: continuous simulation method versus event‐based approach

The proper assessment of design hydrographs and their main properties (peak, volume and duration) in small and ungauged basins is a key point of many hydrological applications. In general, two types of methods can be used to evaluate the design hydrograph: one approach is based on the statistics of storm events, while the other relies on continuously simulating rainfall‐runoff time series. In the first class of methods, the design hydrograph is obtained by applying a rainfall‐runoff model to a design hyetograph that synthesises the storm event. In the second approach, the design hydrograph is quantified by analysing long synthetic runoff time series that are obtained by transforming synthetic rainfall sequences through a rainfall‐runoff model. These simulation‐based procedures overcome some of the unrealistic hypotheses which characterize the event‐based approaches. In this paper, a simulation experiment is carried out to examine the differences between the two types of methods in terms of the design hydrograph's peak, volume and duration. The results conclude that the continuous simulation methods are preferable because the event‐based approaches tend to underestimate the hydrograph's volume and duration. Copyright © 2011 John Wiley & Sons, Ltd.     

A continuous simulation model for design-hydrograph estimation in small and ungauged watersheds

Abstract

A detailed investigation of the behaviour of various hydraulic parameters, using data from rivers in Greece, was conducted in order to explore the universality of features that many natural streams are believed to have in common. Analysis of vertical profiles of temporal mean of horizontal velocities (u) in the longitudinal (river flow) direction and of transverse profiles of depth-mean longitudinal velocities (U) estimated from these vertical profiles, measured at 232 cross-sections of several rivers in Greece, provided valuable information: on the distribution of local roughness coefficients (n_i ) along the wetted perimeter of the cross-sections examined; on the shape of u profiles; on the ratio of maximum to mean cross-sectional velocity, V_max/V_m , and its relation to a dimensionless entropy parameter, M; on the shape of U profiles; and on the normalized intensity, r, of the spatial departure of u velocities from V_m . The similarities among the quantities (u, U, n, V_max/V_m , M, r) analysed in this study and in pertinent literature reveal that the rivers examined exhibit many of the basic features, of rather universal character, shown by other rivers (all over the world) having different geometric and/or other characteristics (aspect ratios, bottom roughness, flow kinematics, etc.). Corresponding differences are also described and explained.     

DETERMINATION OF THE EFFECTIVE POROSITY FOR PARTIALLY PENETRATED AQUIFERS

Abstract

The effective porosity θ _e for partially penetrated aquifers was determined. The model basin sandy aquifer available in the Centre was used. The values obtained for θ _e were in good agreement with the adopted values.