摘要:

A limnological analysis of Cannonsville Reservoir, NY, is presented that focuses on features related to primary production. Monitoring data collected in 1995, a major drawdown year for the impoundment, and long-term data (since 1974), are evaluated. The reservoir demonstrates eutrophic characteristics in most summers, though upper mesotrophic conditions have been observed in some years. The concentration of chlorophyll is found to be the most reliable indicator of trophic state for the impoundment, as tripton (non-living particulate material) interferes with the measures of Secchi disc transparency and total phosphorus (P) concentration as indicators. Evidence is presented that the sediment resuspension process introduced tripton into the water column in 1995 as the reservoir was drawn down. Oxygen was depleted from the hypolimnion during the summer months of 1995; anoxia prevailed above the deep-water sediments for about 1 month. However, a major release of P from the sediments did not occur during this period. Evidence is presented that nitrogen became limiting to phytoplankton growth in mid-summer, and that a sink process(es) operates for die soluble reactive P released in the hypolimnion from the decomposition of organic material. Longitudinal gradients in trophic state indicators and other features of water quality prevail. Bounds for the riverine, transition, and lacustrine zones are presented; the lacustrine zone represents about 80% of the full reservoir volume.

ISSN:1040-2381    

DOI:10.1080/07438149809354325

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The hydrology of Cannonsville Reservoir, a water supply and flow augmentation reservoir for the City of New York, is analyzed. Measurements of components of the hydrologic budget of the reservoir over the entire 30 years of operation are reviewed. The largest tributary is gauged near its discharge to the reservoir; all others are ungauged. Water surface elevation and outflow, in the form of spillway flow, direct releases for flow augmentation, and drinking water withdrawal are monitored. Multiple uses of the reservoir and variations in runoff common to the region result in strong seasonal and interannual variations in hydrology. Spillway flow typically occurs in late winter and spring, and is rare in summer and early fall. Releases, to meet minimum flow requirements in the Delaware River downstream, generally occur only in summer and early fall. Drinking water withdrawal is relatively uniform throughout the year. On average, spill, dam releases, and withdrawal for the water supply have represented 40%, 32%, and 28%, respectively, of the outflow of the reservoir over the 30 years. Reservoir water surface elevation is generally greatest in the spring and lowest in the fall. Reductions in maximum depth of 40% and in storage volume of 75% have occurred in dry years. A hydrologic model was developed to maintain a hydrologic balance and estimate surface inflows from the ungauged portion of the watershed. While estimates based on a simple ratio of ungauged flow to gauged flow may be used for annual averages, a more complex budget calculation based on a 10-day averaging period was used to provide a time series of daily average ungauged inflow. The average annual flushing rate for the 30 years was 2.6 y−1while the range was 1.9 to 3.6 y−1. Use of the entire 30 years hydrologic record is recommended to support forecasting with hydrothermal and water quality models.

ISSN:1040-2381    

DOI:10.1080/07438149809354326

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Observations of the spatial and temporal distribution of temperature in Cannonsville Reservoir over the 1988–1995 period are reviewed, with emphasis on 1994 and 1995. The dominant spatial variations in temperature are in the vertical direction (thermal stratification), with modest spatial variations along the longitudinal axes of the basin. Longitudinal temperature variations were greatest in the spring, with shallow, upstream waters being warmer than at deeper sites downstream near the dam. Diurnal temperature variations of the surface waters of the reservoir were generally less than 2 °C. The variations of temperature of two major reservoir tributaries are also documented. The tributaries are generally warmer than reservoir surface waters in spring, but are cooler through most of the summer and the fall. Diurnal fluctuations in tributary temperature may be significant, with day-night changes as large as 15 °C observed for Trout Creek. A reservoir heat budget calculation for 1995 indicates that inflow/outflow and water surface heat transfer are both important in affecting temperature variations of the reservoir. Direct measurements of incident solar radiation at the reservoir site for a single year allowed calibration of a predictive relationship that may be used in hydrothermal modeling. Estimation of empirical coefficients in predictive expressions for other components of water surface heat transfer was performed using the net water surface heat transfer computed from the heat budget. The implications of these findings for predictive hydrothermal modeling of the reservoir are discussed.

ISSN:1040-2381    

DOI:10.1080/07438149809354327

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A monitoring program consisting of regular observations of temperature and conductivity in the tributaries to and water column of Cannonsville Reservoir from April through November of 1995 is described. The results are analyzed in order to identify and quantify transport processes that affect the distribution of heat and mass constituents. The low temperature of the major reservoir tributary relative to reservoir surface waters in late summer and fall is observed to cause a plunging inflow or negatively-buoyant density current in the reservoir, although evidence is provided that the plunging inflow is not the cause of the observed metalimnetic oxygen minima. A seasonal increase in the specific conductivity of the major tributary in summer creates a longitudinal gradient in conductivity in the epilimnion of the reservoir. A simple analytical model is used to estimate the longitudinal dispersion coefficient in the epilimnion over the summer based on this conductivity gradient. High-frequency observations of temperature using thermistor chains deployed late in the summer stratification period indicate the presence of internal waves in the stratified layers of the reservoir. Current measurements indicate the occurrence of episodes of current speed of a magnitude sufficient to cause sediment resuspension. The application of hydrothermal models to the reservoir to support water quality management is discussed.

ISSN:1040-2381    

DOI:10.1080/07438149809354328

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Two one-dimensional (vertical) hydrothermal models of Cannonsville Reservoir, a water supply serving New York City, were developed and tested. A two-layer model, capable of hindcasting temperature dynamics for two (epilimnion, hypolimnion) completely-mixed, variable-volume layers, was calibrated by determining die seasonal variation of the vertical heat transfer coefficient. This model was used only to hindcast temperature for the spring-fall period of 1995. A multi-layer model (average layer thickness 1.5 m over 50 m maximum depth) was developed that has the capability of forecasting stratification and vertical transport conditions in the reservoir based on specified meteorologic, hydrologic, and reservoir operation conditions. As a part of calibration, the multi-layer model was used to hindcast stratification and vertical transport conditions for the continuous period 1988 through 1995. The model accurately reproduced observed temperature profiles and other observed features such as thermocline depth, rate of hypolimnetic heating, and duration of stratification. A sensitivity analysis indicated that vertical transport of heat to the lower waters of the reservoir in summer is largely associated with advection caused by release of water at the base of the dam; vertical diffusion plays a relatively small role. Model forecasts indicate that stratification characteristics are relatively insensitive to intake location (three intakes over a range of elevation are available), but are more sensitive to the rate of dam release.

ISSN:1040-2381    

DOI:10.1080/07438149809354329

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The successful testing of a two-dimensional hydrothermal/hydrodynamic model, CE-QUAL-W2(t), for Cannonsville Reservoir is documented. The model is calibrated to the detailed temperature data collected in the reservoir (depth-profiles at six locations) over the April-November interval (weekly) of 1995, using comprehensive hydrologic and on-site meteorological forcing data. Further, the frequency of current oscillations predicted for the lower layers matched results of independent determinations made from thermistor chain deployments (two locations). The model is verified through the successful continuous simulation of the observed thermal stratification regime of the reservoir for the 1988–1994 interval, a period in which wide interannual differences were observed related to variations in meteorology and operations. The model performs well in simulating: 1) the timing of stratification and turnover, 2) the duration of stratification, 3) the dimensions of the epilimnion and hypolimnion, 4) the temperature of the layers, and 5) longitudinal variations in these features. The tested model is applied to characterize longitudinal transport of a conservative substance input at the mouth of the principal tributary as a pulse event (e.g., spill).

ISSN:1040-2381    

DOI:10.1080/07438149809354330

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Eight years of monitoring data are reviewed and analyzed for the West Branch of the Delaware River, the major tributary supplying Cannonsville Reservoir: 3 years are from the early 1980s, the other 5 years include 1991–1996. Phosphorus, nitrogen, and sediment loads were measured at the mouth of the West Branch using an approach of intensified sampling during runoff events and routine sampling during baseflow intervals. Total river loads of nutrients and sediment are reported on a water-year basis; selected analytes are reported on a monthly basis. Additionally, phosphorus inputs are partitioned into nonpoint and point source loads. The point source phosphorus load decreased about 75% during the 1990's study period primarily due to upgrades at the largest municipal wastewater treatment plant in the watershed. Annual nonpoint source phosphorus loads were variable over the study period: dissolved phosphorus ranged from 6,600 kg · y−1to 20,800 kg · y−1, while particulate phosphorus ranged from 7,400 kg · y−1to 115,000 kg · y−1. Most of the annual loads of nonpoint source phosphorus, sediment and ammonia were delivered during runoff events. The loads determined through event-based sampling are compared to loads calculated using two other load estimation approaches: an export coefficient technique and fixed frequency sampling combined with the loading software FLUX. The natural variation in nonpoint source loads is examined in the context of setting management goals for improving water quality.

ISSN:1040-2381    

DOI:10.1080/07438149809354331

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Seasonal and longitudinal patterns in downward fluxes and settling velocities of selected particulate constituents, including suspended solids (TSS), organic carbon (C), nitrogen (N), phosphorus (P) and chlorophyll (Cr), are documented for eutrophic Cannonsville Reservoir, NY, for the stratification period of 1995, based on analyses of particulate concentrations in the epilimnion and sediment collected in cylindrical traps deployed below the epilimnion at six different sites. Strong longitudinal gradients in downward flux were observed for all the constituents; the highest rates prevailed in the upstream/riverine zone, the lowest in the downstream/lacustrine zone. These gradients in deposition were driven by gradients of the same form in both the concentrations of the particulate constituents in the epilimnion and the settling velocities of these materials. Substantial temporal variability was observed in particulate species concentrations, and the downward fluxes and settling velocities of these constituents. The mean settling velocities of Cr, particulate organic C, P, and TSS for the lacustrine zone of the reservoir were 0.17, 0.32, 0.88, and 0.73 m · d−1, respectively. The distinctly higher values for TSS, organic C, and P, compared to Crreflect contributions to deposition from non-phytoplankton particles, probably associated with sediment resuspension processes and allochthonous inputs. The fluxes and settling velocities reported here are important in supporting the development and testing of related water quality models for the reservoir.

ISSN:1040-2381    

DOI:10.1080/07438149809354332

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The operation of the sediment resuspension process in Cannonsville Reservoir, NY, a eutrophic flow-augmentation and water supply impoundment for New York City, during the major drawdown year of 1995 is documented. Methodologies used in the assessment included transmissometer profiling; electron microscopy-based physical and chemical characterization of individual particles from the water column, sediments and the principal tributary; analysis of sediment trap collections; and mass balance calculations for total suspended solids (TSS). The resuspension process had several pronounced manifestations. First was the development of a conspicuous benthic nepheloid layer (BNL) which, by mid-summer, extended nearly 10 m above the bottom at one location. Second was the increase in the concentration of inorganic particles in the upper waters as the reservoir was drawn down. These particles, ultimately derived from the watershed, caused increases in turbidity. Third was the measurement of higher downward fluxes in a near-bottom sediment trap compared to a below-thermocline trap deployment and throughout the water column during the fall mixing period. Finally, the TSS deposition rate greatly exceeded estimates of TSS retention for the reservoir. The resuspension phenomenon has important management implications for this and other water supplies because it represents a source of turbidity, and because the resuspended particles interfere with widely adopted signatures of phytoplankton production. Sediment resuspension is probably promoted in this reservoir by the drawdown of the water surface.

ISSN:1040-2381    

DOI:10.1080/07438149809354333

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Longitudinal and temporal distributions of optical properties, and the relative role of selected light attenuating constituents in regulating light penetration, in Cannonsville Reservoir, NY, in 1995 are documented. The analysis is supported by field measurements of light penetration; die angular distribution of irradiance (reflectance); and the spectral quality of penetrating light; laboratory measurements of turbidity, chlorophyll, gelbstoff, and microscopy-based individual particle size and elemental chemistry, and calculations of absorption and scattering coefficients and their components. Longitudinal gradients in attenuating components, and therefore optical properties, prevailed along the main axis of the reservoir; light attenuation and the relative role of scattering decreased with the approach to the dam. Large temporal variations in optical characteristics occurred. These dynamics were mostly controlled by variations in phytoplankton biomass in spring and early summer, when the reservoir was full, but resuspended inorganic tripton (non-phytoplankton particles; suspensoids) became the regulating component as the reservoir was drawn down. Quantitative optical frameworks (models) are applied to simulate light penetration conditions that would have prevailed for scenarios of reductions in phytoplankton biomass and/or inorganic tripton.

ISSN:1040-2381    

DOI:10.1080/07438149809354334

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor