Stella, J. M., & Warner, G. S. (January-February, 2018). Modelling a hydrologic Black-Box. Water Technology and Sciences (in Spanish), 9(1), 101-112, DOI: 10.24850/j-tyca-2018-01-07. Hydrologic simulation models have become an essential tool in the modern world of water management; they are used extensively and play an important auxiliary role in fulfilling the core tasks of water management, in policy preparation, operational water management and research. A physical based hydrologic Black-Box model was created to simulate the water inflows and outflows of the system that could be used for an educational purpose. Then a mathematical model using Stella® software was created to simulate the Black-Box model. The results of the simulations show that the combination of a physical hydrologic Black-Box model and the mathematical model using the Stella® software can helps students understand the basic hydrologic processes.

Accurate measurement of low flow discharges is critical for in stream flow studies. Traditional methods, including weirs and current meters, cannot be applied under all conditions and may by costly in terms of time. The application of an alternative method, Acoustic Doppler Current Profiler (ADCP), is reported for a study of the Fenton River in Connecticut. Examples of the velocity profiles are given, as well as the advantages and limitations compared to the traditional methods.

Many states classify waterbodies according to groups of designated uses, which suggests that classifications may be correlated with water quality. The primary assessments of water quality in the United States (the Biennial Integrated Water Quality Reports) do not consider classification, so the relationship between classification and water quality is untested. Additionally, water quality has been shown to be influenced by watershed land use; however, land use is not typically part of waterbody classification systems. To determine the relationships between waterbody classification, water quality, watershed land cover, and forest fragmentation, we analyzed existing water quality data for the State of Connecticut from the United States Geological Survey and the Connecticut Department of Energy and Environmental Protection and land cover data from the National Land Cover Dataset. Connecticut uses a unique classification system that includes separation of drinking water sources (Class AA) and waterbodies receiving waste water discharges (Class B). Using a comparison of multiple means, we found that Class B waters had higher levels of nitrogen, solids, chloride, sodium, dissolved copper, total iron, and dissolved manganese than Class AA waters. Watersheds upstream of Class B segments had less forest cover, more development and more impervious cover than watersheds upstream of Class AA segments. Class A sites had some similarities in water quality and land cover with Class AA sites and some with Class B sites. The subset of Class B waterbodies with “Class AA-like” water quality also had “Class AA-like” land cover. Based on this and a multiple linear regression analysis, we found that water quality is more closely related to watershed land cover and forest fragmentation than to waterbody classification. Our results suggest that watershed land cover likely is a better proxy for water quality than waterbody classification.

Low stream flows in the Fenton River, part of a hydrogeological setting characterized by glacial stratified drift, forces the University of Connecticut to frequently reduce groundwater withdrawals during the months of June–October. The objective of this study was to investigate stream/aquifer interactions in such a hydrogeologic system in order to increase water withdrawals while minimizing adverse impacts to in-stream flow. A groundwater flow model was developed using MODFLOW to investigate the influence of well location and pumping timing on in-stream flow in the vicinity of the water supply wells. The numerical model comprised detailed geophysical data and decadal hydrologic data (2000–2009) to assess well placement, rest periods and cyclical pumping. The relocation of a water supply well up to 228 m from the river had a positive but minimal improvement to stream flows (<2.83 L/s). When the well field was shut off for more than 45 days, stream flows returned to the no pumping condition with only slight impact at 30 days, whereas a 30 day rest period gave 4 weeks of dampened pumping influence on stream flows. A management scenario of 1 week cyclical pumping between two water supply wells following a 45 day rest period can allow for current restriction thresholds to be reduced by 28.3 L/s with minimal impact to stream flows (7.36 L/s) and would allow additional water to be pumped for all years in which there was a demand for water.

Esta investigacion introduce un enfoque alternativo a la estimacion de escorrentia y maxima descarga durante una tormenta a los metodos comunmente usados como el de la curva y el racional. El metodo de la curva con forma-S, creado por D.A. Hughes, usa las funciones de respuesta de la cuenca para predecir escorrentia, maxima descarga y recesion durante una tormenta. Este metodo describe un evento aislado basado sobre el concepto de fuente de areas expansivas que utiliza un vinculo entre la funcion con forma-S y la proporcion de precipitacion que se transforma en escorrentia. Este enfoque creado por Hughes no ha sido probado en otros lugares aparte de Sudafrica. El metodo de Hughes incluye la aplicacion de la funcion tangente hiperbolica que vincula la altura inicial y el maximo de agua subsuperficial en la cuenca con la escorrentia total que el sistema entrega al rio. Este enfoque fue puesto a prueba en Connecticut e implico el desarrollo de un metodo alternativo para determinar el calculo de los parametros altura inicial y maximo de agua en la cuenca de la funcion con forma-S usando un balance hidrico diario. La aplicacion de este concepto se puso a prueba en el rio Mount Hope, Connecticut, una pequena corriente de agua en Nueva Inglaterra, Noreste de los Estados Unidos. Cuatro acontecimientos, tres en 2004 y uno en 2005, fueron probados y los parametros del modelo calibrados. Las conclusiones generales de la aplicacion de funcion con forma-S muestra que los hidrogramas de respuesta a una tormenta pueden ser predichos con alta exactitud, con variacion en algunos parametros como la altura inicial de agua subsuperficial y la traslacion del tiempo del hidrograma de escorrentia entre eventos, requiriendo calibracion.

This research is related to an alternative approach to runoff estimation. Several watershed response functions or models such the curve number or the rational method have been developed to estimate runoff and peak discharge for a given storm, often for design purposes. The S-shaped curve method, created by D.A. Hughes, use watershed functions response to predict the runoff, peak discharge, and recession curve. This method describes an isolated event flood model based upon the concept of expanding source areas using the S-curve function link with the proportion of precipitation that transforms in stream flow. The stream response function approach of Hughes has been tested in few places had a lack of testing in other areas besides South Africa. The Hughes method includes the application of a hyperbolic tangent function that link the initial and maximum water depth in the watershed with the amount of rainfall in percent of runoff that the system will deliver to the stream. The test of this approach to the northeast of Connecticut in this research involved the development of an alternative method to determine the stream response function including parameters such as the initial watershed storage and the maximum watershed storage using a daily watershed budget. This research tests the application of this concept to the Mount Hope river, Connecticut, a small New England stream, northern USA. Four events, three in 2004 and one in 2005 were tested and the parameters for the model calibrated for those events. The general S-Shaped response shows that individual observed hydrographs can be accurately predicted. However, some parameters such as the initial water storage and the time shift of the direct runoff hydrograph vary among individual events, requiring calibration.

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The aquatic communities in fluvial systems are to a large extent an expression of the dynamic inter- and intra-annual variability in the hydrologic regime of that system and region. To assess the degree to which alteration of the hydrologic regime has affected expressions of ecological integrity, it is necessary to construct reference hydrologic conditions, altered flow regimes, and metrics of change from the reference condition. In this work, an interdisciplinary approach is applied to assess the effects of groundwater extraction on aquatic fauna (brown trout, tessellated darter, and fallfish) in a case study involving the University of Connecticut Fenton River Well Field, Storrs, Connecticut. The study design addressed the interactive components of longitudinal, vertical and temporal connectivity, emphasizing the interaction of biology and, groundwater and surface water hydrology. The development of a simulated discharge time-series and quantification of the degree of effect of groundwater extraction on discharge were central to defining a water management strategy to minimize deviations in intra- and inter-annual habitat availability. Implementation of this strategy involves adjusting groundwater extraction rates based on the magnitude and duration of daily stream discharge. Applying species specific and community habitat thresholds (common, critical and rare) and corresponding maximum durations as fixed flow rules would have avoided the habitat depletion events observed in the summer of 2005.

Mansfield Hollow Lake (MHL) and Willimantic Reservoir (WR) are two reservoir lakes located in eastern Connecticut in the northeastern United States. MHL formed behind the Mansfield Hollow Dam constructed by the U.S. Army Corps of Engineers in 1952 and is primarily fed by the Fenton, Mount Hope and Natchaug Rivers. The WR lies approximately 1-km downstream from the Mansfield Hollow Dam. Total dissolved nitrogen, phosphorus and chlorophyll a measurements indicate the water bodies could be classified as borderline mesotrophic/eutrophic. A steady-state numerical software package (Bathtub) designed to facilitate application of empirical eutrophication models to morphometrically complex reservoirs was used to determine the trophic status in MHL and WR based on different phosphorus and nitrogen loading budgets.The short hydraulic residence times and rapid flushing rates in MHL and WR are directly related to the flow rates in the streams discharging into MHL. The low flow period could significantly increase the hydraulic residence times of these two reservoirs. Therefore, the sampling design emphasized periods of low flow in late August and early September to assess the impact of nutrient inputs to MHL and WR during dry periods. The results of a low flow sampling period (August 2002) were used to calibrate and test the Bathtub model developed for these water bodies.Application of the Bathtub model to differing flow regimes, notably average flows, suggested that nitrogen or phosphorus could limit the productivity and cause eutrophication in the two lakes. Results of this study indicated that the Bathtub model could be used to predict total nitrogen and total phosphorus concentrations with reasonable accuracy, but it might not be a suitable tool for predicting organic nitrogen or algae in rapidly flushing lake systems. To further investigate and validate the assumptions made in this study, more sampling data are needed, especially during high intensity storm events to investigate possible sources of nutrient flow into the two lake system and further calibrate the Bathtub model for the MHL-WR watershed.

AbstractThe Mansfield Hollow Lake (MHL) and Willimantic Reservoir (WR) are two reservoirs located in eastern Connecticut in the north‐eastern USA. The MHL was constructed by the US Army Corps of Engineers in 1952, being primarily fed by the Fenton, Mount Hope and Natchaug Rivers. The WR lies downstream from the Mansfield Hollow Dam. The physical and chemical characteristics of MHL, WR, and the three streams discharging into them were intensively evaluated during four sampling quarters in 2001 and 2002. This study focused on possible sources of eutrophication, and occurrence of trace amounts of selected priority pollutants, in the sediments and waters of MHL and WR. Analytical results for total dissolved nitrogen and phosphorus and chlorophyll‐a indicated that, in terms of eutrophication status, the waterbodies can be classified as mesotrophic. Comparison of the analytical results in this study to historical limnological data reported for lakes in southern New England and eastern Connecticut indicates that the median levels of total nitrogen, total phosphorus, dissolved inorganic carbon, calcium, magnesium, and iron measured in this study were higher than previously reported median values.

A study was conducted to determine the effect of water withdrawals from the University of Connecticut's (Storrs) water supply wells on the fisheries habitat of the Fenton River adjacent to the well field. The study was designed to investigate the relationships between in-stream flow and selected fish habitat in the section of the Fenton River situated in the main zone of influence of the pumping field. With the aid of historical data, new data collection, and mathematical simulation modeling, the relation between the magnitude and timing of groundwater withdrawals on the stage and flow of water in the stream was derived. Fish sampling and habitat modeling were used to assess the effects of human influence on certain reaches of the Fenton River. Among the various water management scenarios studied, several are presented that would optimize water withdrawals, while minimizing adverse effects on the stream flow and in-stream habitat.

This study compared lag time characteristics of low impact residential development with traditional residential development. Also compared were runoff volume, peak discharge, hydrograph kurtosis, runoff coefficient, and runoff threshold. Low impact development (LID) had a significantly greater centroid lag-to-peak, centroid lag, lag-to-peak, and peak lag-to-peak times than traditional development. Traditional development had a significantly greater depth of discharge and runoff coefficient than LID. The peak discharge in runoff from the traditional development was 1,100% greater than from the LID. The runoff threshold of the LID (6.0 mm) was 100% greater than the traditional development (3.0 mm). The hydrograph shape for the LID watershed had a negative value of kurtosis indicating a leptokurtic distribution, while traditional development had a positive value of kurtosis indicating a platykurtic distribution. The lag times of the LID were significantly greater than the traditional watershed for small (< 25.4 mm) but not large ( >= 25.4 mm) storms; short duration (< 4 h) but not long duration ( >= 4 h) storms; and low antecedent moisture condition (AMC; < 25.4 mm) storms but not high AMC ( >= 25.4 mm) storms. This study indicates that LID resulted in lowered peak discharge depth, runoff coefficient, and discharge volume and increased lag times and runoff threshold compared with traditional residential development.

Sedimentation basins and sediment traps are established methodologies for reducing sediment and other pollutants exiting small watersheds such as urban areas and construction sites. However, estimating the trap efficiency or designing a basin or trap to provide a pre-determined trap efficiency, is difficult, especially for dynamic conditions of water and sediment inflow. A conceptual dynamic model, called SedTrap, was developed that can be used to assess the varying removal efficiencies as a storm is routed through different sized basins or traps. The model uses the STELLA® modeling software from Iseesystems, Inc. to build a dynamic model to route both water and sediment through the system. Settling velocities are determined for a range of sediment sizes and temperatures using the Rubey-Watson law and compared to the more traditional Stokes’ law. The variation of efficiencies with time and by sediment size as the basin fills with sediment is also addressed. The results for the example used show a decrease in trap efficiencies with decreasing particle size, which leads to an increase in percent fine material of total sediment load at the outlet of the basin. This “fining” of the material coupled with the higher surface area per mass of the fine particles has implications for changes in the upstream-downstream concentrations of adsorbed contaminants.

In recent years low impact development has grown in popularity as a means PG=59A of reducing nonpoint source pollution from residential areas. The goal of low impact development is to mimic predevelopment site hydrology using design techniques that store, infiltrate, evaporate, and detain runoff in a decentralized, micro-scale manner (Coffman, 2000). The recent interest in the popularity of low impact development is the result of several factors including: new insights into the impact of urban stormwater; new application of stormwater technology, and new stormwater laws. Following the clean-up efforts of point source pollutants in the 1970s and 1980s nonpoint source pollutants were recognized as the leading source of water quality impairment in the United States. Urban runoff significantly impacts estuaries, lakes, and rivers (USEPA, 2002). Inventories, such as the National Resources Inventory, indicate that over the past three decades the amount of urbanized land in the United States has increased and is expected to continue growing. The majority of the techniques used in low impact development are not new but the size and scale have changed. For example, retention basins have been used since the 1970s, but by reducing basin size, adding mulch, plants and possibly …

ABSTRACT: Multivariate analyses were used to develop equations that could predict certain water quality (WQ) conditions for unmonitored watersheds in Puerto Rico based on their physical characteristics. Long term WQ data were used to represent the WQ of 15 watersheds in Puerto Rico. A factor analysis (FA) was performed to reduce the number of chemical constituents. Cluster analysis (CA) was used to group watersheds with similar WQ characteristics. Finally, a discriminant analysis (DA) was performed to relate the WQ clusters to different physical parameters and generate predicting equations. The FA identified six factors (77 percent of variation explained): nutrients, dissolved ions, sodium and chloride, silicacious geology, red ox conditions, and discharge. From the FA, specific conductance, sodium, phosphorous, silica, and dissolved oxygen were selected to represent the WQ characteristics in the CA. The CA determined five groups of watersheds (forested, urban polluted, mixed urban/rural, forested plutonic, and limestone) with similar WQ properties. From the five WQ clusters, two categories can be observed: forested and urban watersheds. The DA found that changes in forest cover, percent of limestone, mean annual rainfall, and watershed shape factor were the most important physical features affecting the WQ of watersheds in Puerto Rico.