R2Cross: A Web-Based Decision Support Tool for Instream Flows
Panagiotis D. Oikonomou , Rumpal Sidhu, Tyler Wible, and Ryan R. Morrison
Research Impact Statement: R2Cross is an intuitive and robust web-accessible tool for assessing instream
ﬂow criteria. It ﬁlls a gap in publicly available online tools as it is uniquely based on a hydraulic rating method.
ABSTRACT: The determination of instream ﬂows for preserving or improving aquatic ecosystems’ health often
includes challenges caused by varied hydraulic conditions, ecological criteria, and socioeconomic considerations.
Despite the abundance of available methodologies, there are few available desktop or online applications
enabling rapid assessment of instream ﬂows that incorporate pertinent geospatial information for the region.
We present R2Cross, a user-friendly, online, instream ﬂow rate calculation tool that was developed for aiding
water allocation decisions in the state of Colorado. The R2Cross tool is the only existing online decision support
tool based on a hydraulic rating method. It estimates hydraulic conditions at different water stages in a stream
reach and compares them to habitat criteria to determine biological instream ﬂow recommendations. Cloud-
based Geographic Information System features and additional tools are incorporated that augment information
and aid in evaluating ecological needs. The development of the R2Cross tool enables an open-access interface for
management authorities and stakeholders to evaluate ecological needs at stream reaches. It automates the
reporting process and could assist in making water management decisions about environmental protection.
Although the R2Cross tool was developed for the state of Colorado, it is generalizable to other stream systems
assuming similar habitat criteria.
(KEYWORDS: instream ﬂows; R2Cross; web-based decision support system; Colorado; hydraulic rating
Most river basins have undergone signiﬁcant
human modiﬁcations, including instream ﬂow
regime changes, threatening aquatic habitat or lead-
ing to degradation in moderate to high degrees
(Dudgeon et al. 2006; V€
osmarty et al. 2010). Pro-
jected global population growth will increase water
demands in all sectors, especially the competition
for water between socioeconomic and environmental
demands (WWAP/UN-Water 2018). Management
methods, tools, and data, which are widely available
and easily accessible by water resources managers
and stakeholders, are needed to provide a system-
atic evaluation of viable allocation alternatives for
environmental needs (Oikonomou 2017). Speciﬁcally,
the natural ﬂow regime plays a crucial role for
maintaining a healthy aquatic habitat (Poff et al.
1997). However, in modiﬁed streams, due to water
diversion and/or storage infrastructure, the natural
spatiotemporal ﬂow variability is lost. Thus, deter-
mination of the minimum environmental ﬂow levels
to protect the aquatic habitat can be difﬁcult when
considering hydraulic conditions, ecological criteria,
and socioeconomic concerns.
Paper No. JAWR-20-0108-N of the Journal of the American Water Resources Association (JAWR). Received August 14, 2020; accepted
June 15, 2021. ©2021 American Water Resources Association. Discussions are open until six months from issue publication.
Colorado Water Institute (Oikonomou), Colorado State University Fort Collins, Colorado, USA; and Department of Civil and Environmen-
tal Engineering (Sidhu, Wible, Morrison), Colorado State University Fort Collins, Colorado, USA (Correspondence to Oikonomou: panagio-
Citation: Oikonomou, P.D., R. Sidhu, T. Wible, and R.R. Morrison. 2021. “R2Cross: A Web-Based Decision Support Tool for Instream
Flows.” Journal of the American Water Resources Association 1–9. https://doi.org/10.1111/1752-1688.12939.
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