Assessment of Hydrologic and Geomorphic Alterations Using

Floodplain Connectivity Metrics

Mark Stone, PhD, PE

Colin Byrne

University of New Mexico

Ryan Morrison, PhD, PE Colorado State University

Overarching Research Themes

(2) Resilience of Socio-Ecological Systems

(1) Hydro-Geo-Ecological Processes

Channel-Floodplain Interface

Interactions of Flow and Vegetation

Floodwave Attenuation

Fish Passage

Environmental Flow Assessments

Resilience to Natural Disasters Floods – Wildfires – Earthquakes

Endangered Species Recovery and Restoration

Vulnerability

Ecosystem Services & System Resilience

Watershed and Floodplain Development & Narrowly Focused Resource Management

Watershed and River Restoration & Holistic Resource Management

As natural systems are degraded, ecosystem services are diminished and system resilience is lost.

Floods, Droughts, Wildfires, Loss of Biodiversity, etc.

Investigate the impacts of flow modifications, historical channel and floodplain modifications, and river restoration on channel/floodplain processes in the Middle Rio Grande.

Study Objectives

cida.usgs.gov

Rio Grande Watershed

An example of efforts to manage rivers more holistically

is through the practice of environmental flows.

Cochiti Dam and Reservoir

(Richard et al. 2005)

-2.5 m

-3 m

-2 m

+5 m

+2 m

Massong et al. (2009)

Rio Grande streamflow above Cochiti Dam (Otowi Gauge)

Upstream of Cochiti

Downstream of Cochiti

Impacts of Cochiti on streamflow

5 kilometers

Historical RG Floodplain

Modern RG Floodplain

Modified structure and function of riparian vegetation

Interrupted energy and nutrient fluxes

Lost maintenance of geomorphic processes and features

Lost dissipation of hydraulic energy and momentum

Reduction in floodwave attenuation

Reduction in groundwater recharge

Modified hyporheic exchange and bank storage

The Impacts

Rio Grande Silvery Minnow - Southwestern Willow Flycatcher - Yellow Billed Cuckoo

Legal Impacts -Three Federally Listed Endangered Species

Methods Applied D-Flow FM 35 km reach – Albuquerque MRG Multiple physical configurations - historical - modern - “restored” Multiple flood conditions - stead state (e.g. 100-yr) - multiple synthetic and gauged floods

D-Flow Model • Unstructured mesh with a

resolution of around 5 to 10 m • Lidar, maps, and survey data were

used to define the topography • Simulations completed at the UNM

Center for Advanced Research Computing using a Linux cluster

• Extensive benchmarking to determine “optimal” number of partitions

Spatial Rating Curves

Water depth

Velocity

Shear Stress

as a function of Q

for every grid point

100

1000

Dis

char

ge (

cms)

Spatial Metrics

Stre

amfl

ow

In

un

dat

ion

D

epth

V

elo

city

Hence we can build a time series of hydraulic characteristics for each grid point in the domain; run stats on each point; and create maps of those stats.

She

ar

Stre

ss

D-Flow FM mesh element boundaries

Digitized boundary of interest

D-Flow FM observation point with temporal output data

MATLAB calculated boundary element with averaged depth-velocity information

Unit flux vectors used to calculate dynamic fluxes across boundaries

Boundary Flux Calculations

Hence, we can investigate spatial and temporally varying fluxes of mass, momentum, and other constituents moving across the channel/floodplain boundary.

Percentage of time inundated Percentage change in inundation

0.01

3

-100

0

Impacts of Cochiti Dam on Inundation Patterns

Hydrodynamics

Hydrology for each scenario

Evidence

Time Dis

char

ge

Bayesian Network Model for Riparian Recruitment

Site Condition

Morrison and Stone. 2014. Water Resources Research.

Decrease in Probability of Riparian Recruitment

Mass Flux between the channel and floodplain

Cu

mu

lati

ve m

ass

tran

sfer

red

to

th

e fl

oo

dp

lain

s (k

g/k

m)

0 10 20 30 40 50 60 70 80 90 100

Time (hrs)

-4

-2

0

2

4

6

8M

ass tra

nsfe

r acro

ss b

ou

nda

ry (

kg

)

# 104

Right CH-FP

Left CH-FP

RS 1

RS 2

RS 3

RS 4

RS 5

RS 6

RS Total

Flood peak leaves reach

Simulated flood peak of 300 cms

Simulated flood peak of 300 cms

Reconstruction of Historical Channel and Floodplain

Historical (1918) Condition 142 cms (5000 cfs)

Modern Conditions

36 km2 6 km2

Discussion and Conclusion

Historical channel, floodplain, and hydrologic modifications have profoundly impacted floodplain processes in places like the Rio Grande.

The spatial assessments of inundation frequency, water fluxes, riparian recruitment, and floodwave attenuation (etc.) provide insights into the roles and significance of various stressors on ecosystem processes and to identify methods to address their impacts.

The temporal assessments provide insights for comparing overall impacts of streamflow and geomorphic modifications between sites or scenarios over an extended period of time.

Boundary flux assessments provide greater insights into underlying physical processes at the floodplain/channel interface.