A Functional Flows Approach to establishing ecological flow criteria for California streams

 

Functional flow components are portions of the annual hydrograph expected to support critical life history needs, habitats, or ecological processes (e.g. flood pulses, recessional flows from Yarnell et al. 2015). Focusing on functional flows allows for establishing the range of environmental flows at critical times of the year, while precluding the need to establish a full “natural hydrograph”. 

Drawing on signal processing theory, we developed a hydrologic feature detection algorithm to quantify functional flow metrics for any daily streamflow time series. This algorithm quantifies the start of the wet season, spring recession, and dry season across climate conditions and natural flow regimes and explicitly incorporates uncertainty estimates.

Functional Flows Calculator (FFC)

The Functional Flows Calculator (FFC) is a web tool for visualizing, downloading, and exploring California's unimpaired streamflow patterns, including natural stream classes, dimensionless reference hydrographs, and functional flow metrics.

 

Dewatering in the intermountain West

As one of the driest and fastest growing states, Utah faces a critical challenge to identify how limited and increasingly uncertain water resources can be more efficiently allocated to meet human and environmental water needs. In dry summers here in Cache Valley, irrigation diversions de-water lowland streams, which can take native trout populations years to recover from. Understanding how aquatic biota respond to changes in streamflow is fundamental to predicting ecological consequences of flow alteration. This in turn can allow us to more accurately assess tradeoffs and propose solutions that benefit both farmers and fish.

 

Fish response to irrigation diversions is mediated by variable water temperature and food availability. In the Blacksmith Fork River, we are monitoring trends in streamflow, groundwater exchange, water temperature, and macroinvertebrates over the summer low flow period. Thermal imagery is being used to pinpoint limiting temperature conditions for fish and help us determine how much water needs to be kept in the river to maintain fish through the hot summer months. We are working with the City of Nibley, Trout Unlimited, and local property owners to develop practical solutions for keeping the determined minimum flows in the river while maintaining agricultural diversions.

 

Hydrologic classification of California

The natural flow regime, including the magnitude, timing, duration, frequency, and rate of change of streamflow, acts as a major control on river ecosystems. We have identified 9 major natural stream classes in California that will be used to help organize regional environmental water management efforts for the state.

Check out our blog post on the California Water Blog!

 

Download the KMZ of the hydrologic classification from the link below:

 

Incorporating topographic variability into

channel classification and mapping

Subreach-scale (<100 m) variations in channel width and depth have rarely been included in channel classifications. However, variability in topographic features of rivers, in conjunction with sediment supply and discharge, produces a mosaic of channel forms that provides unique habitats for sensitive aquatic species. We are investigating the utility of topographic variability attributes (TVAs) in distinguishing channel types and dominant geomorphic processes. Initial results indicate that incorporating TVAs in channel classification provides a quantitative basis for interpreting nonuniform as well as uniform geomorphic processes, which can improve our ability to distinguish linked channel forms and processes of geomorphic and ecological significance. These efforts are now being applied throughout the State of California through partnerships with several academic entities.

 

Regional Environmental Flow Assessment Methodology:

Flow - Form - Function

The extent and timing of many river ecosystem functions is controlled by the interplay of streamflow dynamics (flow) with the river corridor shape and structure (form). However, most river management studies evaluate the role of either flow or form without regard to their dynamic interactions. We are developing a flexible, integrated modeling approach to assess the ecological effects (function) resulting from different flow and form configurations across a basin. 

2D hydrodynamic modeling is used in combination with geomorphic classification and synthetic river corridors to evaluate alternative flow-form-function scenarios at management relevant scales. The use of synthetic, archetypal river models based on mathematical descriptions of geomorphic attributes derived from geomorphic classification in lieu of high-resolution topographic data (i) reduces time and financial requirements, (ii) overcomes site-specific topographic features, and (iii) allows for evaluation of any morphological structure of interest. Ecosystem performance is measured across a suite of functions related to aquatic species, riparian species, and hydrogeomorphic processes.

 

Initial results from this framework highlight critical tradeoffs in ecosystem function performance and emphasize the significance of spatiotemporal diversity of flow and form at multiple scales for maintaining river ecosystem integrity. The approach is broadly applicable and extensible to other systems and ecosystem functions. We are currently using this framework to inform river management and design testing such as impact assessments of proposed changes to flow and form and setting environmental flow standards.