Journal of Hydrologic Engineering

Changes in climatic conditions are expected to affect the hydrological cycle with intensification of extreme rainfall events caused by the disturbance in temperature and other atmospheric variables linked to precipitation. Extreme rainfall change will affect the intensity-duration-frequency (IDF) relationship, used in the design, maintenance, and operation of water infrastructure in Canada. This study presents a comparative analysis of the results from two IDF updating methods: (1) the IDF_CC tool, which applies an equidistance quantile-matching precipitation downscaling algorithm, and (2) the Clausius-Clapeyron (C-C) precipitation-temperature relationship, used with a proposed constant temperature scaling rate. The analyses were conducted using 358 selected Environment Canada hydro-meteorological stations from the IDF_CC tool database with record length longer than 20 years. Results for the future period (2061–2100), are based on the multimodel ensemble of 24 global climate models (GCMs). The difference in (1) projected precipitation and (2) uncertainty range for both IDF updating methods are presented and analyzed. The uncertainty range is defined in this work as the difference between IDF relationships obtained using various GCMs. The C-C temperature scaling method resulted, overall, in higher extreme precipitation projections than the IDF_CC tool for the stations located in the Canadian Prairies (i.e., the provinces of Alberta, Saskatchewan, and Manitoba). Stations located at the east and west coasts of Canada show smaller difference in the projected extremes. A similar pattern is observed for the multimodel ensemble median and the all individual GCMs. The difference in projected uncertainty range for both methods was analyzed for the multimodel ensemble and for representative concentration pathway (RCP) 2.6, RCP 4.5, and RCP 8.5 emission scenarios. The C-C scaling shows a smaller uncertainty range for RCP 2.6 and RCP 4.5, and the IDF_CC tool shows a smaller uncertainty range for the RCP 8.5 scenario (especially for stations located in the Canadian Prairies). The difference in percent uncertainty ranges from $-75\%$ to about 100%, considering all stations across Canada. Both methods show comparable uncertainty range in the future. One significant conclusion is that the high level of uncertainty cannot be avoided, regardless of the method selected for updating IDF curves for future conditions. Use of the precipitation-based IDF_CC tool is recommended because of serious issues in using a constant scaling rate with C-C temperature scaling.

Estimation of intensity-duration-frequency (IDF) functions at ungauged locations is sometimes done using the method introduced by Chen in 1983 [Chen, C. 1983. “Rainfall intensity-duration-frequency formulas.” J. Hydraul. Eng. 109 (12): 1603–1621.], with local rainfall statistics as input. This study applied the Chen method at 9,264 gauged locations in 44 states. The results were used to assess the validity of the fundamental assumptions of the Chen method, and to quantify the accuracy of IDF functions estimated using this method. It is shown that the two fundamental assumptions incorporated in the Chen method are not universally valid across all regions of the United States. Average statewide relative errors are in the range of $-17.2$ to 3.4%, with standard deviations in the range of 5.4–34.6%. Alternative approaches were investigated that will likely yield more accurate estimates of IDF functions.

The vertical distribution of suspended sediment concentration in an open channel is modeled using Rényi entropy. The model, derived by invoking the principle of maximum entropy, is tested against field and laboratory observations by taking into account nonzero sediment concentration at the surface, and is also compared with other entropy-based and deterministic sediment concentration models. The proposed model is found to be in good agreement with observed data, and its prediction accuracy is superior to that of the other models. It is expressed in terms of a dimensionless entropy parameter that is constant along any vertical in a given river cross section. Errors, namely relative bias (RBIAS) and root-mean-square error (RMSE), are calculated for each of the data sets to validate the model and establish its superiority. It is observed that the RMSE of the present model varies from 0.045 to $4.197\mathrm{g}/\mathrm{L}$, and from 16.438 to $74.470\mathrm{g}/\mathrm{L}$, for experimental and field data, respectively, which lie within reasonable limits. In addition, the suspended sediment discharge per unit width is calculated using the Rényi entropy-based models of velocity and sediment concentration. The computed and observed values of sediment discharge are calculated from experimental observations, and it is found that the model can estimate observed values well.

Although the Muskingum equation was proposed nearly 75 years ago, it is still a subject of active research. Despite of its simple form, the real properties of this equation have not been comprehensively explained. This paper proposes a new interpretation of the linear McCarthy’s relation. This relation can be interpreted only together with the storage equation, whereas the Muskingum equation can be derived directly from the system of equations describing the kinematic wave model. Because the Muskingum equation is a semidiscrete form of the kinematic wave equation, all typical effects which may occur in its numerical solution, such as pure translation, attenuation, and oscillations, can be comprehensively explained using the modified equation approach. Taking into account the kinematic roots of the linear Muskingum equation, its new nonlinear version is derived without using any additional McCarthy-type formula. It is shown that the proposed equation is the only correct conservative form of the nonlinear Muskingum equation which simultaneously ensures its dimensional consistency.

Low impact development (LID) is promoted as a sustainable management practice for stormwater in urbanized catchments. While the positive effects of LID features on surface water hydrology and water quality have been investigated, less is known regarding their effects on aquifer recharge. The hydrologic model PCSWMM was coupled with the groundwater model MODFLOW to assess the influence of LID on aquifer recharge in a study area undergoing residential development. The coupled models were calibrated and validated with predevelopment stream flows and groundwater levels from a predominately-forested catchment. PCSWMM was used to quantify net infiltration rates for conventional and LID stormwater practices for the development. Net infiltration rates were then coupled with MODFLOW to determine aquifer recharge and the potential effects on groundwater availability for the development. Results suggested that LID practices would help restore predevelopment aquifer recharge conditions. This study demonstrated a novel approach for assessing the effects of LID stormwater practices on aquifer recharge and groundwater availability in new residential developments.

During the last 40 years, Carolina willow (Salix caroliniana Michx.) expanded into areas previously dominated by herbaceous marshes in the Upper St. Johns River basin (USJRB) of east-central Florida, United States. This change in vegetation affects evapotranspiration (ET). To quantify changes in ET at the community level after willows were removed using herbicides, a two-year field experiment with a randomized complete block design was implemented. The design included an unsprayed control and two different aerially sprayed herbicide treatments and was replicated in four blocks along the Upper St. Johns River. Daily ET was estimated using the Penmen-Monteith equation from July 1, 2014, to August 31, 2016. Cumulative ET difference between the control and treated plots increased substantially during the growing season after herbicide application. Mean annual evapotranspiration was $\mathrm{1,368}\pm 51\mathrm{mm}{\mathrm{y}\mathrm{e}\mathrm{a}\mathrm{r}}^{-1}$ on control plots, $\mathrm{1,096}\pm 137\mathrm{mm}{\mathrm{y}\mathrm{e}\mathrm{a}\mathrm{r}}^{-1}$ on plots treated with Aquasweep or Ecomazapyr herbicide, and $968\pm 117\mathrm{mm}{\mathrm{y}\mathrm{e}\mathrm{a}\mathrm{r}}^{-1}$ on plots treated by Clearcast herbicide. A single-parameter annual ET model derived from a Budyko-type equation was applied to the study area, and the model parameter ($ϵ$) strongly correlated with willow fractional coverage in April. The empirical equation obtained from this study can be potentially used for evaluating the impacts of willow treatment and climate on long-term evapotranspiration in the study area.

Cohesive soil detachment is a complex process that is typically simulated using simplified mathematical models such as the linear excess shear stress equation or power laws. The assumption of linearity between applied shear stresses and erosion rates has repeatedly been questioned, and several nonlinear models have been proposed as alternatives; however, recent studies demonstrated that over the limited range of tested shear stresses, nonlinear models did not describe erosion data significantly better than linear models did. Questions remain regarding the linearity of this relationship at higher ranges of applied shear stress. Laboratory mini jet erosion tests (JETs) were conducted on remolded samples of cohesive soils. A series of statistical tests were then performed to evaluate the suitability of a linear model for describing the relationship between applied shear stress and JET-derived erosion data. For most of the trials, the statistical analysis rejected the assumption of linearity between the erosion rate and applied shear stress. For certain trials, however, it was not possible to conclude on the nonlinearity of the erosion mechanism due to the limited number of erosion data points or the narrowness of the applied shear stress range. Additionally, even though the linear model could provide a good approximation of the erosion data derived using a standard in situ JET procedure typically limited to a narrow shear stress range, its extrapolation potential for prediction of erosion outside of the tested range is limited.