Hesham Fouli

Exchange flow through an opening

This paper presents a theoretical and experimental study of the exchange of fluids of different densities through an opening. Three types of openings are examined: a bottom opening (the opening is at the bottom of a gate), a middle opening (in the middle) and a window opening (the opening is in the middle but does not extend across the width). Simultaneous measurements of velocity field and interface position were obtained using flow visualization and image processing techniques. Experimental results confirm the predictions of the internal hydraulic theory that there are two internal hydraulic controls in the flow through bottom openings, but one control in the middle and window opening experiments. The neglect of non-hydrostatic forces and interfacial mixing in the theory, however, results in a significant underestimate of the exchange rate by more than 50 % in the middle and window opening experiments. The fluctuations in the interface position were caused by Kelvin-Helmholtz instabilities as well as basin-scale internal seiche, and the transition of internally supercritical flow to subcritical flow was caused by the mixing generated by these instabilities.

Reducing False Flood Warnings of TRMM Rain Rates Thresholds over Riyadh City, Saudi Arabia by Utilizing AMSR-E Soil Moisture Information

Rainfall rates and soil moisture content have been recognized as the most critical parameters in flood forecasts; the former known as forcing and the latter as the state variable. The main objective of this article is the incorporation of antecedent soil moisture information to reduce false flood warnings over Riyadh City, Saudi Arabia. The forcing variable was obtained from the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) Real Time (RT) data (3B42RT). Soil moisture (SM) information was obtained from Advanced Microwave Scanning Radiometer (AMSR-E) as the state variable. Long time series SM information (2002–2011) provided Cumulative Distribution Function (CDF) of SM. CDF with 90% was taken as the SM threshold value. Flooding is indicated for rainy dates exceeding the rain thresholds with the previous satellite overpass SM being greater than 90% CDF of the respective month. The methodology removed the false flood warnings substantially when compared to the flood warnings where SM information was absent. The method is robust and simple, and it can be applied on TRMM and AMSR-E follow on missions; like Global Precipitation Measurement (GPM) and Soil Moisture Active Passive (SMAP).

Assessment of a water-harvesting site in Riyadh Region of Kingdom of Saudi Arabia using hydrological analysis

A potential ungauged water-harvesting site was chosen in the central Riyadh Region of Saudi Arabia. A hydrological study was carried out on the catchment area from which runoff water will be diverted to the chosen site. Rainfall depth records from three neighboring rain gauges were used. Runoff volumes and peak discharges for the 2-, 5-, and 10-year storms were estimated using three methods, namely, (a) Soil Conservation Service (SCS) Dimensionless Unit Hydrograph (DUH) method assuming Gumbel distribution for rainfall depth analysis, (b) HEC-HMS modeling, and (c) the modified Talbot formula. The results show that the modified Talbot formula yields an order of magnitude higher peak discharge values for all return periods. The SCS-DUH method and HEC-HMS modeling provide comparable estimates for the peak discharges and runoff volumes. The peak discharges obtained through the Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) model for the 2-, 5-, and 10-year storms are 0.17, 0.83, and 1.34 times than those obtained by the SCS-DUH, respectively. The HEC-HMS runoff volume estimates are 0.18, 0.85, and 1.36 times than those estimated by the SCS-DUH for the 2-, 5-, and 10-year storms, respectively.

Use of interactive multisensor snow and ice mapping system snow cover maps (IMS) and artificial neural networks for simulating river discharges in Eastern Turkey

Basins located in Eastern Turkey are largely fed by snowmelt runoff during spring and early summer seasons. This study investigates the efficiency of artificial neural networks (ANNs) in snowmelt runoff generation. Although ANNs have been used for streamflow simulating/forecasting in the last two decades, using satellite-based snow-covered area (SCA) maps and meteorological observations as inputs to ANN provides a novel basis for estimating streamflow. The proposed methodology is implemented over Upper Euphrates River Basin in Eastern Turkey. SCA data was acquired from Interactive Multisensor Snow and Ice Mapping System (IMS) for an 8-year period from February 2004 to September 2011. Meteorological observations including daily cumulative precipitation and daily average air temperatures were obtained from Turkish State Meteorological Services. The simulation results are promising with coefficient of correlation varying from 0.67 to 0.98 among proposed models. Past days discharge was found to substantially improve the forecast accuracy. The paper presents the expected basin discharge for 2011 water year based on meteorological observations and SCA input.

Interfacial instabilities in two-layer exchange flow over smooth topography

Abstarct: Two-layer exchange flow was modeled in a rectangular channel connecting two reservoirs of water of slightly different densities. A smooth bottom sill was placed within the channel. Kelvin-Helmholtz (K-H) instabilities were generated at the interface of the exchange flow down the sill. Detailed flow measurements were obtained using digital particle image velocimetry (DPIV) for velocity fields, and laser-induced fluorescence (LIF) for interface positions. The measured flow field indicates that K-H instabilities were generated at bulk Richardson number, J, of about 0.07-0.10 with a significantly displaced density field from the center of the shear layer. The generation, growth and propagation of those K-H instabilities were measured from the record of the interface positions. Those instabilities caused significant flow entrainment with the upper layer fluid entrained into the lower layer and the flow rate in the lower layer increasing by about 20% down the sill was found.

Dynamics of the outflow and its effect on the hydraulics of two-layer exchange flows in a channel

Abstract This paper reports that an experimental study is conducted to examine the dynamics of the outflow in two-layer exchange flows in a channel connecting between two water bodies with a small density difference. The experiments reveal the generation of Kelvin-Helmholtz (KH) instabilities within the hydraulically sub-critical flow region of the channel. During maximal exchange, those KH instabilities develops into large-amplitude KH waves as they escape the channel exit into the reservoir. The propagation speed of those waves, their generation frequency and their amplitudes are studied. The dynamics of the outflow and these waves are directly linked to the hydraulic conditions of the exchange flow within the channel.

Transition of two‐layer stratified flow from the slope of bottom topography to a horizontal channel

Abstract An experimental study was conducted to investigate the transition of two‐layer stratified flow from the slope of bottom topography to a horizontal channel. Three experiments, with a reduced gravity of g’ = 1.64, 6.47 and 18.0 cm s−2, were performed. Particle image velocimetry and planar laser‐induced fluorescence were used to obtain the measurements of velocity and concentration fields. The flow rate, obtained from the measured velocity field, increases significantly toward the toe of the topography by almost 40% from that at the sill crest due to the interfacial wave activities. In the horizontal channel, however, the flow rate only increases marginally. Estimates of the composite Froude number indicate that the supercritical flow on the slope of the topography goes through the transition to the subcritical flow in the horizontal channel. The transition is mainly due to the increase in the lower‐layer thickness because of increasing interfacial friction caused by the breaking of interfacial waves, and no internal hydraulic jumps are observed. The measured mean concentration field showed the formation of an intermediate layer of medium density, which increased its thickness with g’ and helped to suppress turbulence. Spectral analysis of the density interfacial fluctuations indicated that the interfacial waves that developed on the slope of the topography broke up downstream of the toe into smaller amplitude waves at larger frequencies. The waves at several channel cross‐sections were also examined.