Page 1

Clear Creek

2015 Watershed Assessment

UCROSS HIGH PLAINS STEWARDSHIP INITIATIVE


Next Steps & Conclusions Water flow in the Clear Creek watershed depends on a complex web of simultaneous, interdependent processes. Using the sophisticated SWAT model developed by our team, we can accurately describe these complexities. This report shows that investment in the landscape through the use of conservation practices can yield tangible benefits for both soil health and sustained creek flow throughout the watershed. In addition, this work establishes baseline conditions to anchor future generations of ranchers and researchers in their management decision-making practices. Further research using this tool could include investigations into other metrics the model is able to assess, such as heat stress, landscape nutrient loss, pesticide transport, changes in crop yields, and fertilizer loads.

Clear Creek

2015 Watershed Assessment

Physical and Empirical Models of Agricultural Systems

Decision Support Systems for Ranchers and Farmers

On the Ground Monitoring and Measurement

UCROSS HIGH PLAINS STEWARDSHIP INITIATIVE


This work is supported by: he results below describe the difference between the ranch hydrology with no grazing management and the four different scenarios tested Mr. Raymond Plank | Yale University School of & Environmental Studies | option The Ucross using the SWAT model. We evaluated theForestry performance of each management usingFoundation two metrics.| Delayed flow describes late Apache | Apache | Bauer Landan and Livestock Steady Stream Hydrology seasonFoundation stream flow (FigureCorporation 13). Sediment yield, indicator for |erosion, represents the total| Kansas mass of sediment exported out of the State University | Wyoming State Engineer’s Office | The Raymond-Saiers Lab at Yale University

T

UCROSS FOUNDATION

Ambika Khadka | Catherine Kuhn

Current Conditions

Riparian Buffers

1% Increase in Organic Content

Earthen Ponds

1 Year of Rotational Grazing

Henry B. Glick, Charlie Bettigole, Lindsi Seegmiller, Devin Routh, Chadwick D. Oliver Clear Creek Watershed: 2015 Watershed Assessment © UHPSI 2015

Key Findings

The Ucross High Plains Stewardship Initiative (UHPSI) is a collaborative effort between the Yale School of Forestry and Environmental Studies and a variety of public institutions, private institutions, and stakeholders in the American West. UHPSI seeks to support land stewardship on the High Plains of the Western United States by enhancing traditional wisdom and intuition with science-based land management solutions. More information is available at http://highplainsstewardship.org

All scenarios improved sediment retention relative to the current watershed rates.

Installing riparian buffer strips can increase late season stream flow by 64-112% in the dry, hot months of August and September.

All four restoration methods will help decrease sediment erosion on the ranch property. Riparian buffers, rotational grazing, earthen ponds and soil amendments will decrease sediment yields by 53%, 22%, 23% and 16% respectively.

CASE STUDY

Yale School of Forestry and Environmental Studies

29


Scenario Modeling Results

Executive Summary

T

he results below describe the difference between the ranch hydrology with no grazing management and the four different scenarios tested using the SWAT model. We evaluated the performance of each management option using two metrics. Delayed flow describes late season stream flow (Figure 13). Sediment yield, an indicator for erosion, represents the total mass of sediment exported out of the

1.6

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1 Delayed Delayed Flow(in) (in) flow

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Precipitation (in) Ranch Hydrology Precipitation (in) Earthen Ponds

Organic Content Increase Organic Content Increase

Rotational Grazing Riparian Buffer Riparian Buffer

Rotational Grazing

W

ater availability is a key concern for communities across the West. The Clear Creek watershed in Wyoming is no exception. The Ucross High Plains Stewardship Initiative (UHPSI) developed the Clear Creek Watershed Assessment in order to enhance existing knowledge about the hydrology of this watershed through the creation of a validated hydrologic model.

The purpose of the model is to predict and to evaluate streamflow and the impacts of management practices on water quality and availability. The model is based on quality controlled-input data and decades of field observations.

We conclude from this research effort that selected management practices can significantly improve late season creek flows. Our results reach agreement with both current research literature and on-the-ground experience showing that holistic rangeland management practices are synergistic with watershed conservation.

Figure 13 (above) shows how each different management type impacts late summer creek flows. Fencing streambanks and planting riparian vegetation (buffers) outperform other scenarios in distributing creek flow throughout the season instead of concentrating discharge during the early spring. Figure 14 (right) shows how each restoration scenario impacts sediment export from the watershed. The middle line of each box represents the median value of that scenario across all the years of the modeling period.

5


Report Overview Scenario 1 | Rotational Grazing This scenario simulates a herd of 5000 adult beef cattle being relocated to new pastures every two weeks from May 1st—November 10th. The scenario accounts for trampling of exposed soils and vegetation, manure production, and animal biomass.

PART 1| BACKGROUND Introduction, Project Objectives, SWAT Model and Clear Creek Watershed Description

Model Development & Accuracy Assessment

This scenario simulates a 1% increase in soil organic content in all of the pasturelands of the ranch. This amendment could be from a variety of sources including manure or compost tea.

Scenario 3 | Riparian Restoration In this scenario, fenced areas are established along Clear Creek’s main channel and its tributaries to exclude grazing. These restored riparian zones are a mixture of deciduous native tree, shrub, and wetland grass species.

CASE STUDY

PART 2 | METHODS

Scenario 2 | Soil Amendments

Scenario 4 | Earthen Ponds In this scenario, earthen ponds are established in the upland draws to store water in the dry, upslope areas for direct use or indirect contributions to local soil moisture and ground water.

27


Ucross Ranch: A Scenario Modeling Case Study

I

n addition to describing overall watershed functions, the SWAT model can also be subset to describe how management choices impact water quality for specific land parcels. While many studies suggest conservation practices yield positive benefits for overall river health, this project assesses these impacts at a much smaller scale. This case study addresses how four hypothetical management choices might influence hydrologic processes on the 21,000-acre Ucross Ranch in comparison to unmanaged rangelands with open range grazing. The four scenarios include rotational grazing (akin to that presently used on the Ranch), the addition of soil amendments, riparian restoration, and the installation of earthen ponds (akin to those already in place on the Ranch). Scenario modeling allows us to evaluate the effects of largescale shifts in management that may be unrealistic to implement, but which shed light on the cumulative effects of small-scale changes that

WATER STORAGE

Show 3 scenarios Compare savings benefits For WY and SY but then points out other things too %% increase in late season flow

Model Outputs & Results

PART 4 | UCROSS RANCH CASE STUDY

Rotational Grazing Soil Amendments Riparian Restoration Earthen Ponds

WATER YIELD

PART 3 | RESULTS & DISCUSSION

Case study examining the watershed impacts of specific management practices

SEDIMENT YIELD

PART 5 | CONCLUSION & NEXT STEPS Potential directions for further modeling work and closing thoughts

7


Introduction

Erosion and Fish Population Health

F

armers, ranchers, researchers and politicians are increasingly interested in measuring the impacts of management practices on ecological systems, including streams and rivers. The creeks draining the Bighorn Mountains in northern Wyoming, including Clear Creek, provide great economic, ecological and cultural value to the adjacent rangelands. The services these creeks provide include clean drinking water for humans and livestock, fish and wildlife habitat, irrigation water, recreation, sediment retention and hydropower.

Early spring runoff has the highest concentrations of sediment. 100000

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Key Findings

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However, more research is needed to understand how specific semi-arid watersheds like Clear Creek will respond to changes in land use and climate. Establishing a baseline understanding of available water resources is the first step to promoting healthy watershed management for this unique system.

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functioning ecosystems that benefit humans and human societies” -Hubbard Brook Research Station, 2013

Average sediment concentration in the water column is 8,843 mg/L, comparable to the Colorado River’s maximum of >10,000 mg/L.

Late season flows can be relatively clear (<250 mg/L) but still are at the upper range of the 100 mg/L threshold considered tolerable by cold-water fish.

0

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“Ecosystem services are services provided by healthy,

Between 73-88% of sediment export occurs during peak runoff caused by spring snowmelt.

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RESULTS

Land management practices directly impact river systems and can determine the quality and quantity of these services. Research has shown sustainable land use can protect streams and in turn, buffer communities from changes in climate and water availability. Strategies such as creek restoration, riparian zone protection and sustainable grazing are thought to help prevent erosion and associated watershed degradation.

2000 2000

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Introduction Yearly Patterns in Erosion Rates

E

xcess sediment is the primary cause of stream degradation in Wyoming. While sediment concentrations vary seasonally, artificially elevated sediment in the water column can be deadly for aquatic life and fish spawning in both cold and warm waters. Cloudy waters can make hunting more difficult for predatory salmonid species and can cloud out bottom-feeders who keep algal growth in check. Beyond total suspended sediment, fine particulate has been shown to be a controlling factor in the impact of sediment loading, or the carrying of solids by the water.

I

n order to provide decision making support for water resources planning, the UHPSI team has created a sophisticated tool, or model, capable of simulating streamflow under different land management strategies. The purposes of the model are to: 

Establish a basic water budget for Clear Creek describing the fate and movement of each drop of incoming precipitation

Quantify water resources specifically relevant to ranching, including annual water yield, soil water content, erosion and groundwater supplies

Simulate how large-scale sustainable management decisions can impact water quality and quantity in a case study focused on the Ucross Ranch

BACKGROUND

Restoring riparian vegetation and stabilizing stream-banks has a tested track record of reducing sediment loads in streams. Healthy, vegetated river corridors can act as filters for surface runoff, sequestering sediments and preventing contaminants from entering the water column. Precipitation 35 4.5 Subbasin 1 Subbasin 2 4 30 Subbasin 3 Subbasin 4 3.5 Subbasin 5 25 Subbasin 6 3 Subbasin 7 Sediment 20 2.5 Precipitation Subbasin 8 Yield Subbasin 9 (in) 2 (tons/acre) 15 Subbasin 10 Subbasin 11 1.5 Subbasin 12 10 Precipitation Subbasin 13 1 Subbasin 14 5 Subbasin 15 0.5 Sediment yield Subbasin 16 by subbasin Subbasin 17 0 0 Subbasin 18 Subbasin 19 Subbasin 20 Subbasin 21 Subbasin 22 Figure 11 (above) shows sediment yield for each of the 22 subbasins in the Clear Creek Watershed, averaged by month for the whole modeling period. Each subbasin has a unique trend in sediment export (shown as a different colored line), which varies with land use, season, soil type and slope. Figure 12 (right) shows the relationship between sediment concentration and water discharge for a typical year.

Project Purpose & Scope

To meet these objectives and accurately capture the complexities associated with agricultural management, our team selected the Soil and Water Assessment Tool (SWAT) model as our primary modeling platform.

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Erosion Rates Across the Watershed

SWAT Model Description

T

he Soil and Water Assessment Tool (SWAT) is a public domain watershed model designed to simulate hydrologic processes in agricultural basins. Created by the USDA Agricultural Research Service and Texas A&M University, the model is specifically suited for investigating the ecological impacts of agricultural land use practices on water yield and quality. With over 30 years of application in research, SWAT is an internationally accepted, robust tool appropriate for assessing the effectiveness of management practices and climate variability at a wide range of scales. SWAT has been also applied to a wide geographic range of watersheds from the Congo to the Mississippi basins.

With its open-source, flexible platform and outstanding global track record of use in agricultural areas, SWAT was the natural choice for this study. This report details the results of this modeling approach for the Clear Creek watershed.

Management practices such as riparian fencing, seen in the photo above, have been shown to increase water quality.

Key Findings 

The total amount of sediment exported from the Clear Creek watershed is 2,979,834 tons per year, or enough to fill 30,000 train cars.

Even though these numbers seem high, they are on par with other rivers in the West. For example, the Colorado river exports up to 200 million tons of sediment per year.

Average annual sediment export for this watershed is 4.3 tons per acre ~ about 1.8 pounds per square yard.

Subbasins with steeper slopes and higher percentages of barren land can have sediment exports up to 1.9 times the average.

RESULTS

The power of the SWAT model lies in its ability to simulate many watershed components important to land managers. These include but are not limited to: timing of peak runoff, total water yield, sediment yield, nitrogen and phosphorus concentrations, reservoir storage, transmission losses from irrigation infrastructure, grazing activity, crop growth rates, soil moisture, pesticide concentrations and many others. At its most basic level, however, SWAT’s strength lies in its ability to simulate how management practices and climatic scenarios impact streamflow.

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Study Area: The Clear Creek Watershed Watershed Attributes Watershed Area: 1,110 square miles

Contributing Streams: 45 +

Average Precipitation: 28.7 inches

Average Annual Temperature: 44.4 ° F

Major Land Use Types: Evergreen forest (17%) and rangeland (46%)

Elevation Range: 3,508-13,375 feet above sea level

Clear Creek Length: 106.1 miles

BACKGROUND

11


Modeling Process Overview

T

he SWAT model is based on well-tested physical principles relating rainfall to stream flow by accounting for all the processes in between. Major model inputs (Table 1) include spatially explicit physical information describing land use, elevation, and soil data. Using these ingredients, the model generates a map of the watershed, divided into subbasins.

Aquifer Recharge and Soil Moisture Infiltration Table 1 Input Data Data Type

Resolution

Source

Properties

Elevation Map

8.9 m

USGS

Slope and elevation

Soil Map

30 m

Soil Survey Geographic Database & superficial geology dataset

Soil texture and properties, underlying geology

Land Use Map

8.9 m/2 m

WorldView-2 satellite image (2011) & National Land cover and land use map Land Cover Database (2006)

Climate Map

6 stations

National Centers for Environmental Predic-

Precipitation, temperature,

RESULTS

Next, the model generates a basic water budget tion’s Climate Forecast System Reanalysis wind speed, solar radiation (Figure 1). This water budget considers inputs such as precipitation, snowmelt, runoff from upstream basins, and groundwater flow, as well as outputs such as evaporation, run-off, aquifer recharge, infiltration and water loss. The arrows in Figure 1 depict the relationships between each process and the storage reservoirs of soil moisture, groundwater, stream water, and the atmosphere. Using this established water budget, the model generates estimates of streamflow and the transport of nutrients, sediment and pesticides on a daily time step for each subbasin. Maps and other output data can then be analyzed to understand basic patterns in water movement in the study landscape.

Key Findings

elevation

land cover

soil type

meteorology

In the Clear Creek watershed, only an estimated 3% of precipitation percolates below the water table to recharge deep groundwater stores in aquifers. Due to this slow recharge rate, replenishment of groundwater stores can take decades.

Depending on land cover and soil type, the upper soil profile can store between 0.94 to 7.78 inches of water at any given time.

During conditions like those in the driest year of the modeling period (2002), soil water content can drop by as much as 25%.

21


Soil Moisture â&#x20AC;&#x201C;Natureâ&#x20AC;&#x2122;s Free Storage

W

Building a Basic Water Budget

hat impacts how much water is stored in soils?

Infiltration is the process of water soaking into soil. The rate of infiltration relies on vegetation density, soil organic content, soil texture and structure. Healthy soils can act like sponges, soaking up water for storage and later use. For water-restricted, semi-arid environments like the Clear Creek watershed, infiltration is key to soil water storage and plant growth. Maintaining this important hydrologic function increases soil moisture, which in turn can sustain forage crops for livestock, minimize erosion, and improve water quality by preventing deposition of salts and sediments.

Finally, infiltration is the key step to deep groundwater recharge. Once precipitation trickles through the top layer of soil, it can penetrate down below the water table to help replenish water stored in aquifers. Aquifer recharge from precipitation is a cost-effective method to augment the groundwater supplies many communities rely on for residential and agricultural use.

METHODS

Conservation practices that increase soil organic content and enhance soil structure, such as no-till farming, can help decrease runoff and help accumulate water entering a basin. In contrast, areas of degraded, bare soil from overgrazing and erosion have very low infiltration rates. These degraded and compacted soils increase rapid surface runoff and reduce infiltration rates, depleting stored soil water.

Figure 7 (above) shows the typical rolling hills and semi-arid rangeland typical of the lower portions of the Clear Creek watershed. Figure 8 (right) illustrates the major processes that help recharge groundwater and replenish soil moisture.

Figure 1 Conceptual schematic of Clear Creek watershed water cycle. The purpose of the SWAT model is to accurately estimate streamflow using a basic water budget approach. A water budget reflects the balance between water in and water out for a region.

13


Assessing Model Accuracy

Streamflow Composition

O

nce the amount of water entering the basin has been established, the model can begin to predict streamflow. We can check model accuracy by comparing the modeled streamflow to the streamflow observed at USGS stream gauges in the basin. Figure 2 shows how closely the model can predict streamflow during the period of study.

RESULTS

Stream gauges measure the height of water in a stilling well (shown in images to the right), and translate this information into estimates of stream flow, or discharge. Officials use these gauges to monitor withdrawals and to conduct flood and drought forecasting. The state of Wyoming is home to 140 of the 8,000 total United States stream gauges. Five of these gauges can be found along the length of Clear Creek.

Clear Creek at Buffalo City Park

Key Findings Clear Creek at Rock Creek Figure 2 (right) offers a quick visual check for model fit. The model estimated stream flow is indicated by the red line and the actual streamflow from the stream gauge is indicated in blue. Figure 5 (above) shows the SWAT model’s simulated monthly patterns in quickflow (surface runoff) and delayed flow (delayed groundwater flow) for the period of simulation. High peaks in the spring are the peak flows caused by snowmelt. Figure 6 (right) is a conceptual diagram showing different movement pathways for creek water.

The mean daily flow in Clear Creek is ~ 207.9 cubic feet per second (cfs) at Arvada, WY. Discharge ranges from 2oo cfs during low flows to over 2,000 cfs during peak spring flooding.

Over 56% of the total flow in Clear Creek is groundwater and soil moisture fed, indicating the importance of promoting land use practices that decrease surface runoff and promote water percolation into the subsurface.

44% of the flow in Clear Creek results directly from surface runoff. Managing rangelands sustainably can help make sure surface runoff water is free of contaminants and excess sediment, protecting water quality and fish habitat in the stream.

19


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METHODS

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Key Findings 

While the model predicts the discharge from 2000-2010, it can be run forward into the future to make predictions about how change in climate, crop coverage or grazing impact water flow in Clear Creek.

The calibrated model is based on seven years of discharge from a vetted USGS stream gauge and can explain 85% of the variability in observed streamflow. This is considered an excellent fit.

The model is able to accurately capture spring snowmelt pulses and periods of low flow in the late summer.

15


Storage and Demand

T

he following conceptual diagram shows how precipitation is partitioned between different hydrologic processes in the greater Clear Creek basin. The numbers represent annual values averaged across all 22 subbasins in the watershed, and form the total water budget. The model includes wetter, high elevation alpine zones as well as the more arid rangelands. Therefore, these numbers represent the balance between the different zones.

10 9 8 7 6 5 Soil Moisture 4 & Snowpack 3 (in) 2 1 0

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Evaporation (in)

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ly Ju

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Snow Storage (in)

RESULTS

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Results: A Holistic Water Budget

Key Findings  Evapotranspiration is the dominant term in the water cycle. Over half of all precipitation entering the basin is shuttled back to the atmosphere through evaporation from bare soils and transpiration by vegetation. Figure 3 (left) shows annual Clear Creek basin averages (in inches) over the period of simulation (2000-2010) for each different component of the water cycle. Figure 4 (right) shows the mismatch between maximum landscape storage of water, as snow pack and soil moisture, and maximum demand for water.

Spring snowmelt causes large annual pulses in discharge. May and June alone account for over 50% of total annual flows.

60% of precipitation — 40% in the form of snow — falls outside the growing season, highlighting the importance of landscape storage to help meet water demand from irrigated crops, rangeland and livestock.

17


Storage and Demand

T

he following conceptual diagram shows how precipitation is partitioned between different hydrologic processes in the greater Clear Creek basin. The numbers represent annual values averaged across all 22 subbasins in the watershed, and form the total water budget. The model includes wetter, high elevation alpine zones as well as the more arid rangelands. Therefore, these numbers represent the balance between the different zones.

10 9 8 7 6 5 Soil Moisture 4 & Snowpack 3 (in) 2 1 0

3 2.5 2 1.5 1

Evaporation (in)

be r

ec em

be r D

em

ov

ob er N

r

O ct

be m

gu st

Soil Moisture (in)

Se pt e

Au

ly Ju

ne Ju

M ay

ril Ap

h M ar c

Fe br

nu a

ry

0

Snow Storage (in)

RESULTS

Ja

Evaporation (in)

0.5

ua ry

Results: A Holistic Water Budget

Key Findings  Evapotranspiration is the dominant term in the water cycle. Over half of all precipitation entering the basin is shuttled back to the atmosphere through evaporation from bare soils and transpiration by vegetation. Figure 3 (left) shows annual Clear Creek basin averages (in inches) over the period of simulation (2000-2010) for each different component of the water cycle. Figure 4 (right) shows the mismatch between maximum landscape storage of water, as snow pack and soil moisture, and maximum demand for water.

Spring snowmelt causes large annual pulses in discharge. May and June alone account for over 50% of total annual flows.

60% of precipitation — 40% in the form of snow — falls outside the growing season, highlighting the importance of landscape storage to help meet water demand from irrigated crops, rangeland and livestock.

17


Clear Creek Discharge Patterns

W

4000

here does the water in Clear Creek come from?

3500

When water enters the basin as precipitation, it can either run off immediately into the stream (quickflow) or soak into the ground and become part of the soil moisture and groundwater system (Figure 6). Once peak snowmelt ends, creek flows are sustained by this cache of soil moisture and groundwater. These low level flows, fed almost entirely by groundwater, are called baseflow or delayed flow. Quickflow can be intensified by drought conditions, which cause the earth to harden and increase fast runoff. This phenomena appears in Figure 5 from 2002-2003, where rain is shunted rapidly into the stream resulting in high quickflows. Rapid surface runoff can lead to lower system water storage, lower baseflow and late season water stress for crops and livestock.

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Quick Quick andand 8 delayed delayed flowflow (in)(in) 6

Rapid runoff

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Model simulation years Quickflow (in)

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2010

Delayed Flow (in)

Figure 5 (above) shows the SWAT model’s simulated monthly patterns in quickflow (surface runoff) and delayed flow (delayed groundwater flow) for the period of simulation. High peaks in the spring are the peak flows caused by snowmelt. Figure 6 (right) is a conceptual diagram showing different movement pathways for creek water.

Observed flow (cfs)

Estimated flow (cfs)

Precipitation (in)

METHODS

16

Key Findings 

While the model predicts the discharge from 2000-2010, it can be run forward into the future to make predictions about how change in climate, crop coverage or grazing impact water flow in Clear Creek.

The calibrated model is based on seven years of discharge from a vetted USGS stream gauge and can explain 85% of the variability in observed streamflow. This is considered an excellent fit.

The model is able to accurately capture spring snowmelt pulses and periods of low flow in the late summer.

15


Assessing Model Accuracy

Streamflow Composition

O

nce the amount of water entering the basin has been established, the model can begin to predict streamflow. We can check model accuracy by comparing the modeled streamflow to the streamflow observed at USGS stream gauges in the basin. Figure 2 shows how closely the model can predict streamflow during the period of study.

RESULTS

Stream gauges measure the height of water in a stilling well (shown in images to the right), and translate this information into estimates of stream flow, or discharge. Officials use these gauges to monitor withdrawals and to conduct flood and drought forecasting. The state of Wyoming is home to 140 of the 8,000 total United States stream gauges. Five of these gauges can be found along the length of Clear Creek.

Clear Creek at Buffalo City Park

Key Findings Clear Creek at Rock Creek Figure 2 (right) offers a quick visual check for model fit. The model estimated stream flow is indicated by the red line and the actual streamflow from the stream gauge is indicated in blue. Figure 5 (above) shows the SWAT model’s simulated monthly patterns in quickflow (surface runoff) and delayed flow (delayed groundwater flow) for the period of simulation. High peaks in the spring are the peak flows caused by snowmelt. Figure 6 (right) is a conceptual diagram showing different movement pathways for creek water.

The mean daily flow in Clear Creek is ~ 207.9 cubic feet per second (cfs) at Arvada, WY. Discharge ranges from 2oo cfs during low flows to over 2,000 cfs during peak spring flooding.

Over 56% of the total flow in Clear Creek is groundwater and soil moisture fed, indicating the importance of promoting land use practices that decrease surface runoff and promote water percolation into the subsurface.

44% of the flow in Clear Creek results directly from surface runoff. Managing rangelands sustainably can help make sure surface runoff water is free of contaminants and excess sediment, protecting water quality and fish habitat in the stream.

19


Soil Moisture â&#x20AC;&#x201C;Natureâ&#x20AC;&#x2122;s Free Storage

W

Building a Basic Water Budget

hat impacts how much water is stored in soils?

Infiltration is the process of water soaking into soil. The rate of infiltration relies on vegetation density, soil organic content, soil texture and structure. Healthy soils can act like sponges, soaking up water for storage and later use. For water-restricted, semi-arid environments like the Clear Creek watershed, infiltration is key to soil water storage and plant growth. Maintaining this important hydrologic function increases soil moisture, which in turn can sustain forage crops for livestock, minimize erosion, and improve water quality by preventing deposition of salts and sediments.

Finally, infiltration is the key step to deep groundwater recharge. Once precipitation trickles through the top layer of soil, it can penetrate down below the water table to help replenish water stored in aquifers. Aquifer recharge from precipitation is a cost-effective method to augment the groundwater supplies many communities rely on for residential and agricultural use.

METHODS

Conservation practices that increase soil organic content and enhance soil structure, such as no-till farming, can help decrease runoff and help accumulate water entering a basin. In contrast, areas of degraded, bare soil from overgrazing and erosion have very low infiltration rates. These degraded and compacted soils increase rapid surface runoff and reduce infiltration rates, depleting stored soil water.

Figure 7 (above) shows the typical rolling hills and semi-arid rangeland typical of the lower portions of the Clear Creek watershed. Figure 8 (right) illustrates the major processes that help recharge groundwater and replenish soil moisture.

Figure 1 Conceptual schematic of Clear Creek watershed water cycle. The purpose of the SWAT model is to accurately estimate streamflow using a basic water budget approach. A water budget reflects the balance between water in and water out for a region.

13


Modeling Process Overview

T

he SWAT model is based on well-tested physical principles relating rainfall to stream flow by accounting for all the processes in between. Major model inputs (Table 1) include spatially explicit physical information describing land use, elevation, and soil data. Using these ingredients, the model generates a map of the watershed, divided into subbasins.

Aquifer Recharge and Soil Moisture Infiltration Table 1 Input Data Data Type

Resolution

Source

Properties

Elevation Map

8.9 m

USGS

Slope and elevation

Soil Map

30 m

Soil Survey Geographic Database & superficial geology dataset

Soil texture and properties, underlying geology

Land Use Map

8.9 m/2 m

WorldView-2 satellite image (2011) & National Land cover and land use map Land Cover Database (2006)

Climate Map

6 stations

National Centers for Environmental Predic-

Precipitation, temperature,

RESULTS

Next, the model generates a basic water budget tion’s Climate Forecast System Reanalysis wind speed, solar radiation (Figure 1). This water budget considers inputs such as precipitation, snowmelt, runoff from upstream basins, and groundwater flow, as well as outputs such as evaporation, run-off, aquifer recharge, infiltration and water loss. The arrows in Figure 1 depict the relationships between each process and the storage reservoirs of soil moisture, groundwater, stream water, and the atmosphere. Using this established water budget, the model generates estimates of streamflow and the transport of nutrients, sediment and pesticides on a daily time step for each subbasin. Maps and other output data can then be analyzed to understand basic patterns in water movement in the study landscape.

Key Findings

elevation

land cover

soil type

meteorology

In the Clear Creek watershed, only an estimated 3% of precipitation percolates below the water table to recharge deep groundwater stores in aquifers. Due to this slow recharge rate, replenishment of groundwater stores can take decades.

Depending on land cover and soil type, the upper soil profile can store between 0.94 to 7.78 inches of water at any given time.

During conditions like those in the driest year of the modeling period (2002), soil water content can drop by as much as 25%.

21


Annual Sediment Export

C

ontrolling erosion and sediment loss is a key concern for land managers for economic and ecological reasons. Slumping and channel degradation cause loss of pasture land and create unwanted repair costs for irrigation infrastructure and fencing, decreasing property value. Increased fine sediments in streams can increase stream temperature, trigger algal blooms, and suffocate fish eggs.

Study Area: The Clear Creek Watershed UPLAND EROSION

Watershed Attributes CHANNEL EROSION

Sediment Yield (tons/acre)

8 7 6 5 4 3 2 1 0

Annual Sediment Yield from 2000-2010

5

Watershed Area: 1,110 square miles

Contributing Streams: 45 +

Average Precipitation: 6-16 inches

Average Annual Temperature: 44.4 ° F

Major Land Use Types: Evergreen forest (17%) and rangeland (46%)

Elevation Range: 3,508-13,375 feet above sea level

Clear Creek Length: 106.1 miles

4 3 2 1

Precipitation & Water Yield (in)

BACKGROUND

While rivers naturally transport sediment off the landscape, conservation practices can ensure this transport is balanced. The following results point out several key trends in sediment export from our modeled estimates.

0 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 Water Yield (in)

Precipitation (in)

Figure 9 (above) shows annual trends in sediment movement during the modeling period. This figure highlights the well-established relationship between rainfall and sediment export. Years with greater precipitation also tend to bring more erosion. Figure 10 (right) shows how sediment export varies throughout the watershed as different subbasins have different rates.

11


Erosion Rates Across the Watershed

SWAT Model Description

T

he Soil and Water Assessment Tool (SWAT) is a public domain watershed model designed to simulate hydrologic processes in agricultural basins. Created by the USDA Agricultural Research Service and Texas A&M University, the model is specifically suited for investigating the ecological impacts of agricultural land use practices on water yield and quality. With over 30 years of application in research, SWAT is an internationally accepted, robust tool appropriate for assessing the effectiveness of management practices and climate variability at a wide range of scales. SWAT has been also applied to a wide geographic range of watersheds from the Congo to the Mississippi basins.

With its open-source, flexible platform and outstanding global track record of use in agricultural areas, SWAT was the natural choice for this study. This report details the results of this modeling approach for the Clear Creek watershed.

Management practices such as riparian fencing, seen in the photo above, have been shown to increase water quality.

Key Findings 

The total amount of sediment exported from the Clear Creek watershed is 2,979,834 tons per year, or enough to fill 30,000 train cars.

Even though these numbers seem high, they are on par with other rivers in the West. For example, the Colorado river exports up to 200 million tons of sediment per year.

Average annual sediment export for this watershed is 4.3 tons per acre ~ about 1.8 pounds per square yard.

Subbasins with steeper slopes and higher percentages of barren land can have sediment exports up to 1.9 times the average.

RESULTS

The power of the SWAT model lies in its ability to simulate many watershed components important to land managers. These include but are not limited to: timing of peak runoff, total water yield, sediment yield, nitrogen and phosphorus concentrations, reservoir storage, transmission losses from irrigation infrastructure, grazing activity, crop growth rates, soil moisture, pesticide concentrations and many others. At its most basic level, however, SWAT’s strength lies in its ability to simulate how management practices and climatic scenarios impact streamflow.

23


Introduction Yearly Patterns in Erosion Rates

E

xcess sediment is the primary cause of stream degradation in Wyoming. While sediment concentrations vary seasonally, artificially elevated sediment in the water column can be deadly for aquatic life and fish spawning in both cold and warm waters. Cloudy waters can make hunting more difficult for predatory salmonid species and can cloud out bottom-feeders who keep algal growth in check. Beyond total suspended sediment, fine particulate has been shown to be a controlling factor in the impact of sediment loading, or the carrying of solids by the water.

I

n order to provide decision making support for water resources planning, the UHPSI team has created a sophisticated tool, or model, capable of simulating streamflow under different land management strategies. The purposes of the model are to: 

Establish a basic water budget for Clear Creek describing the fate and movement of each drop of incoming precipitation

Quantify water resources specifically relevant to ranching, including annual water yield, soil water content, erosion and groundwater supplies

Simulate how large-scale sustainable management decisions can impact water quality and quantity in a case study focused on the Ucross Ranch

BACKGROUND

Restoring riparian vegetation and stabilizing stream-banks has a tested track record of reducing sediment loads in streams. Healthy, vegetated river corridors can act as filters for surface runoff, sequestering sediments and preventing contaminants from entering the water column. Precipitation 35 4.5 Subbasin 1 Subbasin 2 4 30 Subbasin 3 Subbasin 4 3.5 Subbasin 5 25 Subbasin 6 3 Subbasin 7 Sediment 20 2.5 Precipitation Subbasin 8 Yield Subbasin 9 (in) 2 (tons/acre) 15 Subbasin 10 Subbasin 11 1.5 Subbasin 12 10 Precipitation Subbasin 13 1 Subbasin 14 5 Subbasin 15 0.5 Sediment yield Subbasin 16 by subbasin Subbasin 17 0 0 Subbasin 18 Subbasin 19 Subbasin 20 Subbasin 21 Subbasin 22 Figure 11 (above) shows sediment yield for each of the 22 subbasins in the Clear Creek Watershed, averaged by month for the whole modeling period. Each subbasin has a unique trend in sediment export (shown as a different colored line), which varies with land use, season, soil type and slope. Figure 12 (right) shows the relationship between sediment concentration and water discharge for a typical year.

Project Purpose & Scope

To meet these objectives and accurately capture the complexities associated with agricultural management, our team selected the Soil and Water Assessment Tool (SWAT) model as our primary modeling platform.

9


Introduction

Erosion and Fish Population Health

F

armers, ranchers, researchers and politicians are increasingly interested in measuring the impacts of management practices on ecological systems, including streams and rivers. The creeks draining the Bighorn Mountains in northern Wyoming, including Clear Creek, provide great economic, ecological and cultural value to the adjacent rangelands. The services these creeks provide include clean drinking water for humans and livestock, fish and wildlife habitat, irrigation water, recreation, sediment retention and hydropower.

Early spring runoff has the highest concentrations of sediment. 100000

100000

2500

2500

90000

90000

80000 80000 70000 70000

FISH HABITAT

60000 60000

1500 1500

Sedim ent Sediment 50000 50000 (m g/L) (mg/L)

Discharg e Discharge (cubic feet/sec) (cubic feet/sec)

40000 40000

1000 1000

Key Findings

30000

30000

However, more research is needed to understand how specific semi-arid watersheds like Clear Creek will respond to changes in land use and climate. Establishing a baseline understanding of available water resources is the first step to promoting healthy watershed management for this unique system.

20000

500

20000

10000

functioning ecosystems that benefit humans and human societies” -Hubbard Brook Research Station, 2013

Average sediment concentration in the water column is 8,843 mg/L, comparable to the Colorado River’s maximum of >10,000 mg/L.

Late season flows can be relatively clear (<250 mg/L) but still are at the upper range of the 100 mg/L threshold considered tolerable by cold-water fish.

0

0

“Ecosystem services are services provided by healthy,

Between 73-88% of sediment export occurs during peak runoff caused by spring snowmelt.

500

10000

0

0

1999

Temperature (F)

Temperature (F)

Sediment Concentration (mg/L)

2010

Sediment Concentration (mg/L)

Discharge (cfs)

Discharge (cfs)

RESULTS

Land management practices directly impact river systems and can determine the quality and quantity of these services. Research has shown sustainable land use can protect streams and in turn, buffer communities from changes in climate and water availability. Strategies such as creek restoration, riparian zone protection and sustainable grazing are thought to help prevent erosion and associated watershed degradation.

2000 2000

25


Ucross Ranch: A Scenario Modeling Case Study Scenario 1 | Rotational Grazing

I

n addition to describing overall watershed functions, the SWAT model can also be subset to describe how management choices impact water quality for specific land parcels. While many studies suggest that conservation practices yield positive benefits for overall river health, this project assesses these impacts at a much smaller scale. This case study addresses how four hypothetical management choices might influence hydrologic processes on a 21,000-acre ranch with topography and land cover like that of the Ucross Ranch. Each comparison uses as it’s base-line, the average landscape conditions across the Clear Creek watershed at the end of the model validation period. Because of the diverse array of management strategies employed across the watershed, and because of the diverse mixture of data that went into developing the SWAT model, the base-line model does not correspond to any specific parcel of land. It should not be mistaken for the current landscape or management conditions on the Ucross Ranch, for it reflects the landscape, management, and hydrological properties of the watershed as a whole, as of 2010/2011.

This scenario simulates a herd of 5000 adult beef cattle being relocated to new pastures every two weeks from May 1st—November 10th. The scenario accounts for trampling of exposed soils and vegetation, manure production, and animal biomass. It closely mimics the current cattle grazing plan at the Ucross Ranch.

Scenario 2 | Soil Amendments

Scenario 3 | Riparian Restoration In this scenario, fenced areas are established along Clear Creek’s main channel and its tributaries to exclude grazing. These stabilized riparian zones are a mixture of deciduous native tree, shrub, and wetland grass species designed to reduce erosion and slow water movement into the channels.

CASE STUDY

This scenario simulates a 1% increase in soil organic content in all of the pasturelands of the Ranch. This amendment could be from a variety of sources including manure or compost tea. Organic matter is generally thought to increase soil water-holding capacity, infiltration rates, and productivity.

Rotational Grazing Soil Amendments Riparian Restoration Earthen Ponds

WATER YIELD

Scenario 4 | Earthen Ponds In this scenario, additional earthen ponds are established in upland draws to store water in the dry, upslope areas for direct use or indirect contributions to local soil moisture and ground water. In addition to the ponds already in place on the Ranch, ponds were established in 13 subbasins along draws that dry up each August, mimicking natural water storage reservoirs.

27

The four scenarios that were explored include: (1) rotational grazing (akin to that presently used on the Ranch), (2) the addition of soil amendments, (3) riparian restoration, and (4) the installation of earthen ponds (akin to those already in place on the Ranch). Scenario modeling allows us to evaluate the effects of management practices at large geographic scales. At such scales, these practices are often unrealistic to implement, though they help to shed light on the cumulative effects of small-scale

WATER STORAGE

Show 3 scenarios Compare savings benefits For WY and SY but then points out other things too %% increase in late season flow What time scale do I use? How do I decide do use subbasin, year, month to average? All this matrix algebra makes my head want to explode

SEDIMENT YIELD


Scenario 1 | Rotational Grazing This scenario simulates a herd of 5000 adult beef cattle being relocated to new pastures every two weeks from May 1stâ&#x20AC;&#x201D;November 10th. The scenario accounts for trampling of exposed soils and vegetation, manure production, and animal biomass. It closely mimics the current cattle grazing plan at the Ucross Ranch.

Scenario 2 | Soil Amendments

Scenario 3 | Riparian Restoration In this scenario, fenced areas are established along Clear Creekâ&#x20AC;&#x2122;s main channel and its tributaries to exclude grazing. These stabilized riparian zones are a mixture of deciduous native tree, shrub, and wetland grass species designed to reduce erosion and slow water movement into the channels.

CASE STUDY

This scenario simulates a 1% increase in soil organic content in all of the pasturelands of the Ranch. This amendment could be from a variety of sources including manure or compost tea. Organic matter is generally thought to increase soil water-holding capacity, infiltration rates, and productivity.

Scenario 4 | Earthen Ponds In this scenario, additional earthen ponds are established in upland draws to store water in the dry, upslope areas for direct use or indirect contributions to local soil moisture and ground water. In addition to the ponds already in place on the Ranch, ponds were established in 13 subbasins along draws that dry up each August, mimicking natural water storage reservoirs.

27


Scenario Modeling Results

T

he results below describe the difference between the ranch hydrology under the baseline conditions and the four different scenarios tested using the SWAT model. We evaluated the performance of each management option using two metrics. Delayed flow describes late season stream flow (Figure 13). Sediment yield, an indicator for erosion, represents the total mass of sediment exported out of the watershed via the stream (Figure 14). 1.6

4.5

1.4

4

1.2

3.5 3

1 Delayed Delayed Flow(in) (in) flow

2.5

0.8

2

0.6

1.5

0.4

1

0.2

0.5

0

Precipitation Precipitation (in) (in)

0

Precipitation (in) Ranch Hydrology Precipitation (in) Earthen Ponds

Organic Content Increase Organic Content Increase Rotational Grazing

Rotational Grazing Riparian Buffer Riparian Buffer Baseline hydrology

Figure 13 (above) shows how each different management type impacts late summer creek flows. Fencing streambanks and planting riparian vegetation (buffers) outperform other scenarios in distributing creek flow throughout the season instead of concentrating discharge during the early spring. Figure 14 (right) shows how each restoration scenario impacts sediment export from the watershed. The middle line of each box represents the median value of that scenario across all the years of the modeling period.


T

he results below describe the difference between the ranch hydrology with no grazing management and the four different scenarios tested using the SWAT model. We evaluated the performance of each management option using two metrics. Delayed flow describes late season stream flow (Figure 13). Sediment yield, an indicator for erosion, represents the total mass of sediment exported out of the

Riparian Buffers

1% Increase in Organic Content

Earthen Ponds

1 Year of Rotational Grazing

CASE STUDY

Current Conditions

Key Findings 

All scenarios improved sediment retention relative to the current watershed rates.

Installing riparian buffer strips can increase late season stream flow by 64-112% in the dry, hot months of August and September.

All four restoration methods will help decrease sediment erosion on the ranch property. Riparian buffers, rotational grazing, earthen ponds and soil amendments will decrease sediment yields by 53%, 22%, 23% and 16% respectively.

29


Next Steps & Conclusions Water flow in the Clear Creek watershed depends on a complex web of simultaneous, interdependent processes. Using the sophisticated SWAT model developed by our team, we can accurately describe these complexities. This report shows that investment in the landscape through the use of conservation practices can yield tangible benefits for both soil health and sustained creek flow throughout the watershed. In addition, this work establishes baseline conditions to anchor future generations of ranchers and researchers in their management decision-making practices. Further research using this tool could include investigations into other metrics the model is able to assess, such as heat stress, landscape nutrient loss, pesticide transport, changes in crop yields, and fertilizer loads.

Clear Creek

2015 Watershed Assessment

Physical and Empirical Models of Agricultural Systems

Decision Support Systems for Ranchers and Farmers

On the Ground Monitoring and Measurement

UCROSS HIGH PLAINS STEWARDSHIP INITIATIVE


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Clear Creek 2015 Watershed Assessment  

This booklet details findings from a Soil and Water Assessment Tool (SWAT) model for the Clear Creak watershed in north-central Wyoming, USA...

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