WWETAC Projects

Project Title: Western riparian threats assessment

Status: Completed

Principal Investigators: David M. Theobald, Warner College of Natural Resources, Colorado State University; John Norman, David Merritt, Rocky Mountain Research Station, Streams Systems Technology Center

E-mail Contact: davet[at]warnercnr.colostate.edu

Web: Southwest Watershed Team Home Page

Summary: The purpose of this project is to develop a scientifically sound approach to assess threats to fluvial riparian areas in the western United States. Our first objective is to review, analyze, and develop methods to characterize ecological condition of riparian areas. This includes:

  • Review and analyze existing approaches to mapping threats to ecological conditions.
  • Coordinate and incorporate expertise and feedback from riparian ecologists from government and nongovernment agencies
  • Acquire broad-scale GIS data on biophysical characteristics, including ecoregions, hydrology, DEMs (30 m), land use/cover (NLCD), housing density (SERGoM, Census data), etc.

Our second objective is to evaluate ecological condition riparian areas by watersheds, which includes:

  • Develop framework for organizing threats in watersheds
  • Identify surrogates for threats for GIS data
  • Develop model of relationship between threat and response

Our third and final objective is to develop assessment and ranking of threats by 5th or 6th-code watersheds. This will include:

  • Compute local condition for each reach catchment area
  • Compute basin-area-weighted accumulation
  • Summarize ecological condition by 5th or 6th code
  • Generate maps depicting relative degree of threat for Western United States

Key Issues/Problems Addressed: The purpose of this project is to develop a scientifically sound approach to assess threats to fluvial riparian areas in the western United States.


Study Objectives:

1. Characterize and describe ecological condition of riparian areas in the western United States;
2. Develop a qualitative valuation of ecological condition furnished by these landscapes; and
3. Conduct a qualitative assessment and ranking of threats to each of these values by 6th code watersheds in the western USA.

Status: We completed the first objective, resulting in an overview presentation (PPT). We have compiled and processed the broad-scale GIS data needed, including datasets on:

  1. Digital Elevation Model (30 m)
  2. National Hydrography Data (1:100k)
  3. Streetmap 2006 roads
  4. Landfire EVT and biophysical setting
  5. Housing density (SERGoM)
  6. Climate (precipitation and temperature, 1900 – 2000)
  7. Beetle outbreak (199-2006)

All of these data are now integrated using the FLoWS tools to construct a consistent flow-direction based platform.

We have refined our approach to move away from using single indicators and then developing response curves (i.e. a functional response curve relating ecological condition to indicator values). This posed two challenges: first, there is a paucity of literature to fully support and justify the development of these curves, rather we would have to rely on expert judgment only; second, we found it difficult to synthesize the independent indicators as there are likely various and non-linear interactions among indicators that would likely cause difficulty in interpreting the relationship between riparian condition/threat and indicators.

Consequently, we are emphasizing measuring three aspects of riparian areas:

  1. modification of hydrologic flow regime
  2. erosion and sediment delivered to streams
  3. footprint of human-modified land cover/use in valley bottom zones.

We are measuring hydrologic flow regime using the flow modification indicator we have described in past presentations. For the second aspect, we have employed (and refined) a process-based model (RUSLE – revised universal soil loss equation) to estimate sediment production as a function of a variety of change or threat scenarios (see table below). We have used Landfire land cover data to drive the RUSLE model and have invested significant resources in distinguishing road, commercial/industrial, and controlled-access urban areas (i.e. airports, military bases, etc.) that are simply lumped as urban/built-up in Landfire classes (21, 22, 23, and 24).

Figure 2: South Platte watershed showing sediment load delivered to streams reflecting current land cover (Landfire EVT), accumulated downstreams (and assuming all sediment is left in reservoirs and does not continue downstream).

South Platte Watershed

To understand the relative priority of a watershed to a threat, we will compute cumulative distributions of our three measures for each scenario. We will then be able to compare not only overall distributions of changes, but each HUC will be attributed with its raw (absolute) measure as well as normalized (through decile distributions) scores.

Table 1. Threat/change scenarios to be modeled to assess threats to riparian areas.


Discharge flow modification (Vogel’s regression)

Sediment (RUSLE)

Human-modified land cover in potential riparian zone & lateral connectivity


PRISM 1900-1940 (mean annual, +/- 1SD)

LandFire BpS

LandFire BpS


PRISM 1940-2000 (mean annual +/- 1 SD)?

LandFire EVT
StreetMap 2006 roads
SERGoM 2000

LandFire EVT
StreetMap 2006 roads
SERGoM 2000
Impervious surface


Beetle kill ~2007

Tamarisk invasion?


Precip/temperature 2030

LandFire EVT
StreetMap 2006 roads
SERGoM (2030 and change 2000 – 2030)

Future tamarisk expansion?? LandFire EVT
StreetMap 2006 roads
SERGoM (2030 and change 2000 – 2030)
Impervious surface

Dam storage increases based on population growth

LandFire Fire Regime/historic variation
StreetMap 2006 roads
SERGoM (2030 and change 2000 – 2030)


Deliverables: We are making great progress in developing the datasets of these three measures. We will develop and deliver a map of western US that provides a relative ranking of overall threats to riparian areas by 5 or 6 digit HUCs. This will include the spatial data (in Geodatabase format) used to generate the overall threat assessment.

Project ID: FY06TS14