Abstracts:Streamflow is often intermittent in arid and semi-arid regions. Stochastically simulated data play a key role in managing water resources with intermittent streamflows. The stochastic modeling of intermittent streamflow that incorporates the seasonality of key statistics is a difficult task. In the current study, the product model was tested to simulate the intermittent monthly streamflow by employing the periodic Markov chain (PMC) model for occurrence and the periodic gamma autoregressive (PGAR) and copula models for amount. The copula models were tested in a previous study for the simulation of yearly streamflow, resulting in successful replication of the key and operational statistics of historical data; however, the copula models have never been tested on a monthly time scale. The intermittent models were applied to the Colorado River system in the present study. A few drawbacks of the PGAR model were identified, such as significant underestimation of minimum values on an aggregated yearly time scale and restrictions of the parameter boundaries. Conversely, the copula models do not present such drawbacks but show feasible reproduction of key and operational statistics. We concluded that the copula models combined with the PMC model is a feasible method for the simulation of intermittent monthly streamflow time series.

Abstracts:Employing a dataset of 658 large storm-events from 15 South Korean watersheds (48.6–249.63 km²), this study established the initial abstraction (I a ) as 2% of the rainfall amount (obtained based on three different scenarios), instead of the originally assumed 20% of the maximum potential retention (S) in the Soil Conservation Service Curve Number (SCS–CN) model. After investigating 8 different models, including the original SCS-CN and its inspired modified models, it was found that lower values of the initial abstraction coefficient (λ) exhibited better runoff estimation than the fixed λ (=0.2) as lower λ < 0.2 was recommended by researchers and supported by this work for CN values calculated from observed storm-events. To reduce errors in runoff estimation, CNs should be calibrated using observed rainfall-runoff data from regional watersheds. The proposed model, which incorporates the newly suggested initial abstraction based on rainfall-runoff rank-order data, outperformed in 14 out of 15 watersheds. Using the optimized/calculated CN values, the proposed model ranked first (as best) based on the evaluation of three different performance indices, followed by the model of Hawkins et al. (2002), one of the models of the Mishra and Singh, and the original SCS-CN model respectively. Owing to a significant degree of agreement between the observed and calculated runoff, the proposed model is recommended for field applications in this study area.

Abstracts:In this study, a series of laboratory experiments were conducted to measure the run-up heights on plane slopes and wave pressures on vertical structures resulting from solitary waves, which represent the characteristics of tsunamis well. The measured run-up heights were compared with predictions of available run-up formulas. Pressure transducers were used to measure time histories of wave pressure according to wave height and thus to record pressure distributions in laboratory experiments. The force of each incident solitary wave was estimated by integrating pressure distributions, for both square and cylindrical columns. Experimental measurements agreed well with the predictions of existing empirical formulas frequently used in design of coastal structures.

Abstracts:For floodwater utilization, seasonal flood-limited water level (FLWL) plays a more and more role in compromising between flood control and beneficial use in reservoir operation during flood season. The prerequisite of determining a seasonal FLWL is that flood control risks should not be increased in reservoir operation as compared with the original operating rule using a fixed FLWL. In this paper, a risk analysis model for deriving seasonal FLWL that considers uncertainties of hydrology, hydraulic condition and reservoir volume is proposed and developed. The risk analysis model consists of three modules: the first is a hydrological uncertainty analysis module, the second is a hydraulic uncertainty analysis module, as well as the third is a reservoir volume uncertainty analysis module. The acceptable risk constraints are given, and the upper limitation of seasonal FLWL is estimated by using Monte Carlo simulation. The China’ Wanjiazhai reservoir (WR) is selected as a case study. The application results show that (1) the hydrological uncertainty and the reservoir volume uncertainty are major contribution factors to seasonal FLWL while the discharge capacity uncertainty is inapparent influence of seasonal FLWL, (2) the most reasonable upper limitations of seasonal FLWL in WR during main-flood and post-flood seasons are 972.3 and 974.1 m, respectively, which considers hydrological uncertainty, minimum hydraulic capability and minimum reservoir volume. The relative magnitudes of seasonal FLWL and the flood water utilization rates during main-flood and post-flood seasons are 0.65% and 61.05%, as well as 0.84% and 81.60%, respectively. Seasonal FLWL can effectively enhance flood water utilization rate without lowering the annual flood control standard compared with annual FLWL.

Abstracts:In this study, a methodology is presented and demonstrated for combined estimation of regional specific yield and distributed recharge using double water-table fluctuation (DWTF) technique and geographical information system (GIS) in a hard-rock aquifer system of semi-arid regions. The study area was divided into 25 zones and groundwater budget components were computed for both wet and dry seasons using 11-year period (1996–2006) data. In each zone, the regional specific yield was estimated by applying the WTF technique for dry seasons and the rainfall recharge was estimated by applying the WTF technique for wet seasons. Zone-wise rainfall–recharge relationships were established using regression technique. Thereafter, the specific yield and recharge estimates were used with GIS to generate their maps. Surface-water bodies were found to significantly contribute to groundwater recharge. This finding underscores the need for adopting rainwater harvesting in the study area to enhance recharge. The regional specific yields were found to range from 0.038 to 0.002, whereas the mean rainfall recharge was found to vary from 0.5 to 10.9 cm. The box–whisker plots of z-scale transformed specific yield revealed the greatest spatial variation. The spatial and temporal variations of the rainfall recharge in the study area are statistically significant (p < 0.05 and CV > 30%). The developed rainfall–recharge relationships were found to be ‘highly significant’ (r ² ≥ 0.54, p < 0.05) in four zones, ‘moderately significant’ (0.54 > r ² ≥ 0.36, p < 0.01) in ten zones and ‘insignificant’ (r ² < 0.36) in the remaining zones.

Abstracts:Among other flood forecasting tools, fuzzy logic is one of a simple and flexible approach which can be implemented in river basins where adequate hydrologic data is available and not good enough to use in a more sophisticated model. This paper assesses the potential of fuzzy logic approach for real time flood forecasting using the minimum implication function type Mamdani fuzzy inference system by applying the model to the Kelantan River basin in Malaysia. The developed models were tested for forecasting the downstream water levels of Guilemard and Kuala Krai stations using upstream hourly telemetric water levels of Dabong and Tualang stations. The membership functions (MFs) of triangular shapes with several fuzzy rule sets were utilized to check the efficiency of the fuzzy logic approach for the Kelantan River flood forecasting. For the Guilemard station, models of 8, 10 and 15 rules' sets were tested. In the calibration and validation events, the Guilemard station models' achieved MAE, ranges 0.35–0.45 m, N–S coefficient, ranges 0.87 – 0.89 and Coefficient of Determination ranges, R² ranges 0.91–0.95. The water level prediction model developed for the Kuala Krai station consisted of 19 rules with triangular shape MFs. It shows the ranges for MAE: 0.26–0.76 m, N–S coefficient: 0.78–0.93 and R²: 0.91–0.96 in calibration and validation periods. The efficiencies of the developed models show acceptable levels according to the tested performance indicators implying the potential of establishing a flood forecasting system by using the fuzzy logic approach in the Kelantan River basin, Malaysia.

Abstracts:This paper proposes an analytical model to predict the lateral distribution of streamwise velocity for flow in a curved channel with vertical sides, based on the depth-integrated Navier–Stokes equations. The model includes the effects of bed friction, lateral turbulence and secondary flows, where the additional secondary flow is approximated by a linear function of the lateral distance, as demonstrated by the limited data which are available. Two analytical solutions for the depth-averaged velocity are obtained, one for a flat bed and another for a bed with a transverse slope. Two parameters (denoted by m and n herein), which define the secondary flow, have been examined to analyze how they affect the velocity distribution in these two cases. Comparison of the analytical results with the limited experimental data available shows that the proposed model predicts the lateral distributions of depth-averaged velocity well. Further studies are needed to validate the values of the model parameters (m and n) for bends with different geometric properties.

Abstracts:To investigate the feasibility of suspending sediments in storm-drains in coastal cities using tidal energy, numerical and physical experiments are carried out to understand the behaviour of a dam-break generated flow from an infinite reservoir (the sea) into a positively inclined channel of limited width (the storm-drain). The numerical results are obtained using LES as these yield the most accurate predictions of the results from the physical experiments. The hydrodynamics of the flow inside the channel are controlled by the large volume of water in the reservoir and cross waves are generated in the channel due to its limited width. On relatively steep slopes, the bed shear stress results indicate that sediment suspension is likely to occur under the leading edge of the flow while on mild slopes suspension of sediments may occur over a great distance into the channel and for a long duration after the initial dam-break.

Abstracts:This paper describes the results of an experimental study on the turbulence characteristics of flow through bed profile of a laboratory channel that was degraded by detachment of its bed material consisting of sand–gravel mixture. The measurements of velocity and turbulence characteristics over the degraded bed profile were made at three locations along the degraded bed profile using an ADV. The maximum value of turbulence intensity and the Reynolds shear stress were found to occur at the level of bed surface existing before the detachment and these values decreased towards the flow surface. The magnitude of turbulence intensities and Reynolds shear stress are observed to reduce, as one moves towards the downstream along the degraded bed profile which signifies that vortex structure weakened by bed profile degradation. Quadrant analysis was performed which demonstrated the importance of ejection and sweep phases in sediment detachment and transport. Highest occurrence probabilities are found for sweep and ejection event. The other two events i.e. outward and inward interactions are found to have very small occurrence on the probabilities. Variation of occurrence probability with hole size (H) is also discussed.

Abstracts:The extent of faecal contamination in soils and water is still poorly known in rural tropical areas despite its important consequences on both human health and the economy. Here we explore the sources, pathways, and spatio-temporal dynamic of contamination in rivers of a rural tropical area at different spatial and temporal scales. Concentrations of Escherichia coli (E. coli), a faecal indicator bacteria (FIB), were measured in the Nam Khan river, tributary of the Mekong river (North Lao PDR). Measurements were made from the headwaters to the main stream under contrasted hydrological conditions (i.e. during base flow and stormflow) and during the wet and dry seasons in 2011. The results show that E. coli contamination is controlled by both land use (i.e. stock of bacteria brought to the soil surface by the faeces of human and livestock) and hydrology (i.e. contribution of overland flow to the river discharge). Direct point-source contamination is of minor importance in this rural watershed, however, during high discharge the concentration of FIB frequently exceeds 5000 MPN 100 mL⁻¹. The E. coli module of the Seneque/Riverstrahler model was adapted to the context of the Nam Khan river, validated with field observations and used to analyse future scenarios of faecal contamination (changing demographic trends and improvements in wastewater management). We found that the risk of worsening FIB contamination was more related to the predicted future rural exodus and to wastewater management practices rather than to an increase in demographic pressure in these upland systems.