Return of a giant: DNA from archival museum samples helps to identify a unique cutthroat trout lineage formerly thought to be extinct

Currently one small, native population of the culturally and ecologically important Lahontan cutthroat trout ( Oncorhynchus clarkii henshawi , LCT, Federally listed) remains in the Truckee River watershed of northwestern Nevada and northeastern California. The majority of populations in this watershed were extirpated in the 1940s due to invasive species, overharvest, anthropogenic water consumption and changing precipitation regimes. In 1977, a population of cutthroat trout discovered in the Pilot Peak Mountains in the Bonneville basin of Utah, was putatively identified as the extirpated LCT lacustrine lineage native to Pyramid Lake in the Truckee River basin based on morphological and meristic characters. Our phylogenetic and Bayesian genotype clustering analyses of museum specimens collected from the large lakes (1872–1913) and contemporary samples collected from populations throughout the extant range provide evidence in support of a genetically distinct Truckee River basin origin for this population. Analysis of museum samples alone identified three distinct genotype clusters and historical connectivity among water bodies within the Truckee River basin. Baseline data from museum collections indicate that the extant Pilot Peak strain represents a remnant of the extirpated lacustrine lineage. Given the limitations on high-quality data when working with a sparse number of preserved museum samples, we acknowledge that, in the end, this may be a more complicated story. However, the paucity of remnant populations in the Truckee River watershed, in combination with data on the distribution of morphological, meristic and genetic data for Lahontan cutthroat trout, suggests that recovery strategies, particularly in the large lacustrine habitats should consider this lineage as an important part of the genetic legacy of this species.

Modeling the hydrodynamic interactions between the main channel and the floodplain at McCarran Ranch in the lower Truckee River, Nevada

This study applied the two-dimensional AdH (adaptive hydraulics) hydrodynamic model to a river reach to analyze flood hydraulics on complex floodplains. Using the AdH model combined with bathymetry and topographic data from the United States Geological Survey (USGS) seamless server and the United States Army Corps of Engineers (USACE), we intended to examine the interactions between the channel and floodplain of a 10 km stretch at McCarran Ranch, which is located at the lower Truckee River in Nevada. After calibrating the model, we tested the dependence of the modeling results on mesh density, input parameters, and time steps and compared the modeling results to the existing gauged data (both the discharge and water stage heights). Results show that the accuracy of prediction from the AdH model may decline slightly at higher discharges and water levels. The modeling results are more sensitive to the roughness coefficient of the main channel, which suggests that the model calibration should give priority to the main channel roughness. A detailed analysis of the floodwater dynamics was then conducted using the modeling approach to examine the hydraulic linkage between the main channel and floodplains. We found that large flood events could lead to a significantly higher proportion of total flow being routed through the floodplains. During peak discharges, a river channel diverted as much as 65 % of the total discharge into the floodplain. During the periods of overbank flow, the transboundary flux ratio was approximately 5 to 45 % of the total river discharge, which indicates substantial exchange between the main channel and floodplains. The results also showed that both the relations of the inundation area and volume versus the discharge exhibit an apparent looped curve form, which suggests that flood routing has an areal hysteresis effect on floodplains.

Climate change and non-stationary flood risk for the upper Truckee River basin

Future flood frequency for the upper Truckee River basin (UTRB) is assessed using non-stationary extreme value models and design-life risk methodology. Historical floods are simulated at two UTRB gauge locations, Farad and Reno, using the Variable Infiltration Capacity (VIC) model and non-stationary Generalized Extreme Value (GEV) models. The non-stationary GEV models are fit to the cool season (November–April) monthly maximum flows using historical monthly precipitation totals and average temperature. Future cool season flood distributions are subsequently calculated using downscaled projections of precipitation and temperature from the Coupled Model Intercomparison Project Phase 5 (CMIP-5) archive. The resulting exceedance probabilities are combined to calculate the probability of a flood of a given magnitude occurring over a specific time period (referred to as flood risk) using recent developments in design-life risk methodologies. This paper provides the first end-to-end analysis using non-stationary GEV methods coupled with contemporary downscaled climate projections to demonstrate the evolution of a flood risk profile over typical design life periods of existing infrastructure that are vulnerable to flooding (e.g., dams, levees, bridges and sewers). Results show that flood risk increases significantly over the analysis period (from 1950 through 2099). This highlights the potential to underestimate flood risk using traditional methodologies that do not account for time-varying risk. Although model parameters for the non-stationary method are sensitive to small changes in input parameters, analysis shows that the changes in risk over time are robust. Overall, flood risk at both locations (Farad and Reno) is projected to increase 10–20% between the historical period 1950 to 1999 and the future period 2000 to 2050 and 30–50% between the same historical period and a future period of 2050 to 2099.

Modeling inundation of seasonally flooded wetlands at McCarran Ranch on Truckee River, USA

This paper among the first presents the application and validation of a hydrodynamic model (Adaptive Hydraulics model, AdH) of the McCarran ranch. We use the AdH model with topographic data by combining the DEM data from USGS seamless server and the ESRI tin data from United States Army Corps of Engineers (USACE) to predict floodplain inundation for a river reach of ~10 km located at lower Truckee River in Nevada state. We tested the mesh independence, sensitivity of input parameters and time steps, and then compared the modeling results to the existing gauged data (both the discharge and water stage heights). Results show that the accuracy of prediction from AdH model can decline slightly at higher discharge and water levels. The modeling results are much sensitive to the roughness coefficient of main channel, suggesting the model calibration should give priority to the main channel roughness. The simulation results suggest that large flood events could lead to a significantly higher proportion of total flow that routed through the floodplains. During peak discharge, a river channel constriction diverted as much as 65% of the river's 512.3 m3s−1 discharge into the floodplain. During the overbank flow, the transboundary flux ratio is about 5–45% of the total river discharge. Results also showed that both the relation of inundation area and volume between the discharge exhibit an apparent looped curve form.