Rafael G. Quimpo

Capacity-weighted water distribution system reliability

Abstract The reliability that water will be available at demand points of a distribution system may be expressed in terms of several measures. An earlier measure bases the reliability only on simple connectivity of the demand point to the water source. This has been criticized as not representative of real systems since adequacy of water supply requires not only connectedness to a source, but also that a specified amount of flow must be delivered. To address this deficiency, a capacity-weighted reliability index is suggested. Two capacity-weighted measures are possible. A strict capacity measure excludes the reliability calculation paths which do not fully meet the demanded flow. A more realistic measure is one which takes into account partial satisfaction of demand through a weighted index. The procedure for calculating this reliability index is developed and illustrated in this paper.

Sedimentation basin performance at highway construction sites

Sedimentation basins (SBs) are commonly used during highway construction for erosion and sedimentation pollution control as well as for attenuation of overland storm waters. In order to evaluate the sediment removal capacity of these SBs, four basins were selected for monitoring from a new highway construction that extends I-99 to I-80, in Pennsylvania. Between September 2004 and August 2005, ten sampling trips were conducted during which basin inlet and outlet water samples were obtained. The SB samples were analyzed for pH, color, turbidity, total suspended solids (TSS), volatile suspended solids (VSS), total and dissolved iron, magnesium, manganese, aluminum, calcium, sulfate and phosphate. The data showed peaks in concentrations of TSS, total aluminum, total manganese, total iron and total phosphate that closely correlated to localized rainfall peaks. For certain samples, the concentration of TSS in the outlet was higher than the TSS concentration at the basin inlet, suggesting sediment re-suspension. In general SBs managed high flows during wet weather events, but were not effective in capturing particulates. This paper discusses the need for Best Management Practices (BMPs) for the design of SBs that reflect contemporary concerns for management of particle removal and to control the release of particulate-bound metals. This paper also evaluates the water quality impacts of naturally occurring acidic drainages into SBs, as several acidic seeps with pH in the range of 5-6 and having high dissolved concentrations of metals (Fe, Mn, Mg and Ca), sulfate and phosphate were observed draining into the SBs.

Spatial heterogeneity and models of surface runoff

Abstract The spatial heterogeneity of the processes and parameters which determine surface runoff has given rise to different attempts to improve on the lumped system representation of the watershed. Various techniques, ranging from the distributed formulation, component-type lumped models and the use of partial source-area and geomorphological concepts are reviewed in order to identify possible areas of future inquiry. The synthesis of the innovative contributions of the recent approaches is suggested.

REDUCTION OF SERIALLY CORRELATED HYDROLOGIC DATA

Abstract The need for specifying water availability in terms of its time sequence and distribution, rather than in terms of lumped quantities or flow duration, has given rise to data asquisition programs which use shorter sampling intervals. Shorter time intervals, in turn, has resulted in serially correlated observations. In order to determine the reliability of design variables derived from these observations, it is necessary to reduce these data to an equivalent series of independent observations, or find the effective lenght of the series. A general parametric formula is developed for the effective number of observations for the second order autoregressive process, which has been found to apply to the series of mean daily river flows. Different values of the parameters were programmed in a digital computer to obtain tables for data reduction.

ON THE VARIABILITY OF SEASONAL PARAMETERS IN HYDROLOGIC TIME SERIES

Abstract The attempt to preserve seasonal characteristics in the modeling of streamflow time series has given rise to a decomposition scheme wherein a random process is superimposed on another periodic process. Strong empirical evidence indicates that under this hypothesis, the amplitude and phase of the periodic component are quite variable. The nature of this variability is examined using simulated time series whose structure is assumed known. It is found that the random component tend to distort estimates of the amplitude and phase so that a relatively long series is needed to estimate parameters (60 years of simulated monthly data to give coefficients of variation of 0.16 for the amplitude and 0.20 for the phase angle). The variation of the phase angle and amplitude, as determined by demodulation is highly dependent on a “signal-to-noise” measure defined as the ratio of the variance explained by the periodic component to the variance of the random component.