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Estimating Surface Runoff and Landcover Changes for the Thorn Creek Watershed

Authors: Mike Michalek, Alison Keener, and Kauthar Al-Habsi

Introduction: It is well-known that pervasive land-use changes since the 1800’s have

contributed to an increase in nonpoint source water pollution, which the Environmental

Protection Agency (EPA) has identified as one of the leading sources of water quality

impairment nationwide. With over twenty-seven reports of impaired waterbodies within the

Muskegon River Watershed alone, illicit sources of surface water runoff have received attention

from environmental regulators and environmental advocates alike. Modified pathways and rates

of water flow across a landscape can be effectively measured using GIS software in conjunction

with established hydrologic parameters. Our project will estimate a runoff curve number within

ESRI’s ArcGIS to demonstrate how deforestation and urban development within the last 150

years has increased storm water surface runoff in the Thorn Creek Watershed of North-Central

Lower Michigan, a sub-basin within the Muskegon River Watershed. Surface runoff in the Thorn

Creek Watershed exits the catchment at the lowest point in Evart, Michigan (310 meters above

sea level).

Study Area:The Thorn Creek Watershed is a sub-watershed of the greater Muskegon River

Watershed (Figure 1). The lowest point in the watershed is located in the city of Evart, Michigan

at an elevation of 310 meters above sea level. Runoff is collected in the Muskegon River, which

flows through the study area from the northeast, exiting to the southwest in Evart. Higher

elevations are recorded in the hilly regions North and South of the Muskegon River. Climate

records indicate high precipitation levels in the 1800s, record low levels around1930s and a

continual increase since that time.

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Figure 1. The Thorn Creek Watershed in reference to the greater Muskegon River Basin.

Objective/Data Types: The objective of our study is to quantify the hydrologic impact that

changes in landuseover a 150 year time periodhas had on the region. Tracking landcover change

and amount of runoff associated with cover types between the times in question is also an

objective of this study. Data for this study was gathered from multiple sources. Soil data for the

region was collected and produced by the Natural Resource Conservation Service (NRCS) and is

available online in their Soil Survey Geographic Database (SURGO). All land-use data was

acquired from the Michigan Center of Geographic Information (MCGI). Climate data was

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obtained from Jeffrey Andresen, PhD., in the Michigan State University Department of

Geography.

Landcover: North-Central Michigan has experienced many changes in landcover over the past

150 years (Figure 2). Pre-settlement landcover in the study area consisted of mainly coniferous

and mixed forests with large wetlands. Michigan’s logging era, which lasted from the 1830’s

until the 1910’s dramatically impacted the forested reaches of the region (Figure 3&4). Once

heavily forested lands now transitioned into bare and highly vulnerable landscapes. Runoff rates

soon increased as the naturally sandy soils in the region became exposed to overland flow. As

agriculture increased on the cleared landscape, wetlands became drained to make room for

grazing.Conservation efforts soon encouraged the planting of trees, which soon transitioned into

the areas national and state forests. These changes are observed in Figure 1, notice the dramatic

decrease in forests and wetlands, with increased agriculture.

Data for the three time periods in question differed in type and thoroughness. For

example, 2001 landcover data was downloaded in raster format, while 1800 and 1978 was

rasterized from a vector format. Impervious surfaces on the 2001 landcover file appear much

clearer than in the 1800 and 1978 shapefiles. Roads are even distinguishable (Maps on Page 5)

on the 2001 map of the study area. These differences in shapefile accuracy may be identifiable in

our results, the authors believe that the amount of differential accuracy will play only a minute

role in the overall results.

 

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Maps showing 1800, 1978, and 2001 Landcover and Hydrologic Soil Groups.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Runoff: Surface runoff is the amount of water that is transported via over land flow. Reasons for

runoff range from highly infiltrated soils (full of water), highly impervious surfaces, thin

landcover, heavy precipitation events, and/or soil type. This study implemented soil type

(hydrologic soil groups), topography (flow accumulation), and land cover type (Anderson runoff

rates) to decipher the amount of runoff a region within the study area would likely contribute to

the overall watershed (Maps on page8). Flow accumulation was also generated in ArcGIS to

estimate where in the watershed water tends to flow. The runoff map (derived with the curve

number formula) was used to assign a weight to each cell in the flow accumulation analysis. This

differentiates our methods from a simple flow accumulation analysis, which by default assigns

an equal weight value to each cell in the raster grid. Evaluating changes of flow accumulation

throughout time enabled us to observe how changes in landcover have affected the natural flow

of runoff in the study area (Map & Figure on page 9).

Our analysis/production of landcover change and flow accumulation in ArcGIS can be

evaluated in Figure 6. Data was first rasterized (if it was vector) and clipped to our study area,

minimizing processing time. Next, the rasters were reclassified to represent the Anderson

landcover model and the USGS soil hydrologic groups (Figure 5). Each landcover year/dataset

was then combined with the classified soil hydrologic group file, to combine two of our three

runoff factors. The lookup tool was then initiated to create a new raster by looking up values

found in a table of the input raster, providing a runoff curve number.Raster calculator was then

run to calculate total runoff in the watershed.

A DEM of the study area was resampled to match the 30X30 pixel size of the landcover

dataset and then filled to get rid of “holes” in the data. Next, the DEM was run through the flow

direction tool to provide flow directions on the landscape. Flow accumulation was finally

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processed by using the runoff dataset previously discussed with the flow direction dataset,

producing the map on page 9.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 6.Flow chart showing processes used to determine flow accumulation in the study area.

 

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Maps showing 1800, 1978, and 2001 Runoff Curve Numbers,indicating the amount of runoff a region was expected to contribute to the overall watershed.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Map showing 1800 Flow Accumulation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Conclusion: The study area has experienced extreme deforestation (besides a slight increase

from 1978 – 2001) in the historical record. Decreasing forested landcover has noticeably

changed runoff values for much of the study area. Draining of swampland and an increase

ofagriculture, urbanization , and shrubland have also changed runoff values since the 1800’s.

Runoffhas increased in many locations throughout the watershed because of the previous stated

landuse changes. Flow Accumulationmimics the variability of precipitation Michigan has

received between the 1800’s and 2001 (Figure 7). Future work should incorporate annual

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evapotranspiration rates along with precipitation, soil type, landcover, and topography when

examining flow accumulation.

Figure 7. Flow Accumulation correlated with Annual Precipitation.

References:

Andresen et al., 2009.The Influence of Land Cover Type on Surface Hydrology in Michigan. Chapter 11 in Understanding Climate Change: Climate Variability, Predictability, and Change in the Midwestern United States, S.C. Pryor, ed. ISBN 978-0-253-35344-3, Indiana University Press, Bloomington, IN.

Werner, J. Hydrologic Soil Groups: Chapter 7. Part 630 Hydrology National Engineering Handbook. 210-VI-NEH, May 2007. USDA NRCS.

 

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