1. Watershed P (in) Q (in) ET +ΔS (in) Rock Creek 37.37 13.02 24.25
Annual total rainfall vs runoff for the Rock Creek and Big Creek watersheds (closed diamonds). Data represent streamflow records available for the respective watersheds: 1984–2014 for Rock Creek and 1973–1985 and 2002 for Big Creek. Average annual total rainfall vs runoff is shown for the respective basins (open diamonds) to demonstrate that average rainfall is similar in the two watersheds, suggesting that the difference in runoff is due to land cover.
Rainfall-runoff data from Big Creek watershed should have been plotted on the graph provided in the previous class and average values for annual rainfall and runoff calculated. The average values for the water balance equation are
Watershed P (in) Q (in) ET +ΔS (in)
Rock Creek
Big Creek
Students should be able to answer several questions about the data:
Is input, or rainfall, similar between the two watersheds? Answer: The average annual rainfall in Big Creek watershed is similar, less than an inch different. But the range of annual rainfall values from Big Creek watershed lies within, or overlaps, the range of Rock Creek watershed.
This makes it useful for comparing runoff for data pairs where rainfall is similar. For example, annual rainfall values between 36–37 in occur for both watersheds 2–3 times.
For the same amount of rainfall (i.e., 36–37 inches), in which watershed would runoff be expected to be greater? Answer: Big Creek watershed.
Is it a result of more rainfall? Answer: No, since average annual precipitation is deliberately constant (i.e., 36–37 in).
Is storage similar or different between the two watersheds? Answer: Different, less in Big Creek. More in Rock Creek.
Explore these differences.
Why might this be the case? Brainstorm for several minutes, allowing the students to develop potential reasons. Write them on the board, organizing them as you go into whether reasons are related to P, ET, or ΔS. Because of the previous discussion, P may be ruled out, but it could be that the distribution of rainfall within the year is important. This could account for the variability in runoff for a given watershed for similar amounts of rainfall. Most other suggestions can be organized around ET or ΔS or related factors.
Rainfall data are from for north central (Rock Creek) and northeast (Big Creek) Ohio.
Runoff data are derived from U.S. Geological Survey streamflow data from (Rock Creek) and (Big Creek).

2. Rainfall-runoff data from both watersheds. This slide may be omitted
Rainfall-runoff data from both watersheds. This slide may be omitted. It shows the 1:1 relationship between rainfall and runoff as well as the 2:1, 3:1, and 4:1 relationships. Emphasizes the magnitude of the difference between the rainfall-runoff relation between Rock Creek and Big Creek.
Rainfall data are from for north central (Rock Creek) and northeast (Big Creek) Ohio.
Runoff data are derived from U.S. Geological Survey streamflow data from (Rock Creek) and (Big Creek).

3. Big Creek at Cleveland OH USGS Gaging Station 04208502
Latitude  41°27'01", Longitude  81°43'18"
Cuyahoga County, Ohio
Hydrologic Unit Code
Drainage area 35.3   mi2
Realtime Stage Data:
Big Creek at Cleveland Ohio
Rock Creek at Tiffin OH
USGS Gaging Station
Lat 41°06'49", long 83°10'06“
Seneca County, OH
Hydrologic Unit
Drainage area 34.6 mi2
Realtime Stage and Discharge Data:
Rock Creek at Tiffin Ohio
Runoff data from the Rock Creek and Big Creek watersheds in Ohio are used in this module. Relative location, basic watershed characteristics, and a link to the real-time streamflow data from the U.S. Geological Survey are included here.
Google Earth can be used in lieu of the watershed and land cover slides for Rock Creek and Big Creek watersheds.
U.S. Geological Survey station data from
U.S. Geological Survey station data from

4. This will be a review of the Rock Creek watershed, for close comparison with the Big Creek watershed. Aerial image of the Rock Creek watershed, illustrating land use. Note that most of the land cover is associated with agriculture. Urban land use dominates the area around the outlet. Tiffin, Ohio, is the community at the outlet and downstream of it.
A Google Earth KMZ file of the drainage divide and network for each watershed is included in the Description and Teaching Materials section of Unit 1.3.

5. This will be a review of the Rock Creek watershed, for close comparison with the Big Creek watershed. Land cover in 2011 in the Rock Creek watershed. Land cover was taken from the National Land Cover Database. Though not natural land cover, this type of land use maintains a pervious surface and infiltration of water.
A Google Earth KMZ file of the land cover for each watershed is included in the Description and Teaching Materials section of Unit 1.3.
Rock Creek watershed is dominated by
Cultivated Crops—areas used for the production of annual crops, such as corn, soybeans, vegetables, tobacco, and cotton, and also perennial woody crops such as orchards and vineyards. Crop vegetation accounts for greater than 20% of total vegetation. This class also includes all land being actively tilled.
then
Pasture/Hay—areas of grasses, legumes, or grass-legume mixtures planted for livestock grazing or the production of seed or hay crops, typically on a perennial cycle. Pasture/hay vegetation accounts for greater than 20% of total vegetation.
Deciduous Forest—areas dominated by trees generally greater than 5 meters tall, and greater than 20% of total vegetation cover. More than 75% of the tree species shed foliage simultaneously in response to seasonal change.

6. Aerial image of the Big Creek watershed, illustrating land use
Aerial image of the Big Creek watershed, illustrating land use. In contrast to Rock Creek watershed, land cover here is dominantly urban and suburban. This is the greater metropolitan area of Cleveland, Ohio.
A Google Earth KMZ file of the drainage divide and network for each watershed is included in the Description and Teaching Materials section of Unit 1.3.
Big Creek watershed is dominated by
Developed, Low Intensity—areas with a mixture of constructed materials and vegetation. Impervious surfaces account for 20% to 49% percent of total cover. These areas most commonly include single-family housing units.
then
Developed, Medium Intensity—areas with a mixture of constructed materials and vegetation. Impervious surfaces account for 50% to 79% of the total cover. These areas most commonly include single-family housing units.
Developed High Intensity—highly developed areas where people reside or work in high numbers. Examples include apartment complexes, row houses and commercial/industrial. Impervious surfaces account for 80% to 100% of the total cover.

7. Land cover in 2011 in the Big Creek watershed
Land cover in 2011 in the Big Creek watershed. Land cover was taken from the National Land Cover Database. Developed land cover, associated with urbanization and suburbanization, is impervious and largely drained from the watershed by way of impervious culverts and stormwater sewers.
A Google Earth KMZ file of the land cover for each watershed is included in the Description and Teaching Materials section of Unit 1.3.
Big Creek watershed is dominated by
Developed, Low Intensity—areas with a mixture of constructed materials and vegetation. Impervious surfaces account for 20% to 49% percent of total cover. These areas most commonly include single-family housing units.
then
Developed, Medium Intensity—areas with a mixture of constructed materials and vegetation. Impervious surfaces account for 50% to 79% of the total cover. These areas most commonly include single-family housing units.
Developed High Intensity—highly developed areas where people reside or work in high numbers. Examples include apartment complexes, row houses and commercial/industrial. Impervious surfaces account for 80% to 100% of the total cover.

8. Classification Description
2011 National Land Cover Database Classification Descriptions
Class
Value
Classification Description
Water 11
Open Water - areas of open water, generally with less than 25% cover of vegetation or soil. 12
Perennial Ice/Snow - areas characterized by a perennial cover of ice and/or snow, generally greater than 25% of total cover.
Developed 21
Developed, Open Space - areas with a mixture of some constructed materials, but mostly vegetation in the form of lawn grasses. Impervious surfaces account for less than 20% of total cover. These areas most commonly include large-lot single-family housing units, parks, golf courses, and vegetation planted in developed settings for recreation, erosion control, or aesthetic purposes. 22
Developed, Low Intensity - areas with a mixture of constructed materials and vegetation. Impervious surfaces account for 20% to 49% percent of total cover. These areas most commonly include single-family housing units. 23
Developed, Medium Intensity – areas with a mixture of constructed materials and vegetation. Impervious surfaces account for 50% to 79% of the total cover. These areas most commonly include single-family housing units. 24
Developed High Intensity -highly developed areas where people reside or work in high numbers. Examples include apartment complexes, row houses and commercial/industrial. Impervious surfaces account for 80% to 100% of the total cover.
Barren 31
Barren Land (Rock/Sand/Clay) - areas of bedrock, desert pavement, scarps, talus, slides, volcanic material, glacial debris, sand dunes, strip mines, gravel pits and other accumulations of earthen material. Generally, vegetation accounts for less than 15% of total cover.
Forest 41
Deciduous Forest - areas dominated by trees generally greater than 5 meters tall, and greater than 20% of total vegetation cover. More than 75% of the tree species shed foliage simultaneously in response to seasonal change. 42
Evergreen Forest - areas dominated by trees generally greater than 5 meters tall, and greater than 20% of total vegetation cover. More than 75% of the tree species maintain their leaves all year. Canopy is never without green foliage. 43
Mixed Forest - areas dominated by trees generally greater than 5 meters tall, and greater than 20% of total vegetation cover. Neither deciduous nor evergreen species are greater than 75% of total tree cover.
Class, value, and descriptions of different land covers from the 2011 National Land Cover Database (NLCD). The classification system is modified from the Anderson Land Cover Classification System. Full documentation of the NLCD can be found at
adapted from legends and descriptions for the NLCD available from

9. Classification Description (cont.)
2011 National Land Cover Database Classification Descriptions
(cont.)
Class
Value
Classification Description (cont.)
Shrubland 51
Dwarf Scrub - Alaska only areas dominated by shrubs less than 20 centimeters tall with shrub canopy typically greater than 20% of total vegetation. This type is often co-associated with grasses, sedges, herbs, and non-vascular vegetation. 52
Shrub/Scrub - areas dominated by shrubs; less than 5 meters tall with shrub canopy typically greater than 20% of total vegetation. This class includes true shrubs, young trees in an early successional stage or trees stunted from environmental conditions.
Herbaceous 71
Grassland/Herbaceous - areas dominated by gramanoid or herbaceous vegetation, generally greater than 80% of total vegetation. These areas are not subject to intensive management such as tilling, but can be utilized for grazing. 72
Sedge/Herbaceous - Alaska only areas dominated by sedges and forbs, generally greater than 80% of total vegetation. This type can occur with significant other grasses or other grass like plants, and includes sedge tundra, and sedge tussock tundra. 73
Lichens - Alaska only areas dominated by fruticose or foliose lichens generally greater than 80% of total vegetation. 74
Moss - Alaska only areas dominated by mosses, generally greater than 80% of total vegetation.
Planted/
Cultivated 81
Pasture/Hay – areas of grasses, legumes, or grass-legume mixtures planted for livestock grazing or the production of seed or hay crops, typically on a perennial cycle. Pasture/hay vegetation accounts for greater than 20% of total vegetation. 82
Cultivated Crops – areas used for the production of annual crops, such as corn, soybeans, vegetables, tobacco, and cotton, and also perennial woody crops such as orchards and vineyards. Crop vegetation accounts for greater than 20% of total vegetation. This class also includes all land being actively tilled.
Wetlands 90
Woody Wetlands - areas where forest or shrubland vegetation accounts for greater than 20% of vegetative cover and the soil or substrate is periodically saturated with or covered with water. 91
Emergent Herbaceous Wetlands - Areas where perennial herbaceous vegetation accounts for greater than 80% of vegetative cover and the soil or substrate is periodically saturated with or covered with water.
Class, value, and descriptions of different land covers from the 2011 National Land Cover Database (NLCD). The classification system is modified from the Anderson Land Cover Classification System. Full documentation of the NLCD can be found at
adapted from legends and descriptions for the NLCD available from

10. 2011 Land Cover in the Rock Creek and Big Creek Watersheds
Land cover in the Rock Creek and Big Creek watersheds in Rock Creek and Big Creek watersheds reflect a common change in land cover as urban centers and suburbia grow outward. Following deforestation for agricultural purposes at the time of Euro-American settlement, the change from agricultural land uses to urban land uses is the most pervasive. Many of your students will have come from homes that were built in the past 30–50 years in suburbia. It is valuable to point this out.
If you are using Google Earth, the "Show historical imagery" function could be used for an area with which you are familiar that shows urban or suburban development. It was covered in Unit 1.1 with examples if you prefer to use those. The pervious agricultural land cover is increasingly impervious with developed land cover.

11. Rate of Farmland Conversion (a cumulative area the size of Indiana)
to Non-farming Uses
>2500 acres/day*
(a cumulative area the size of Indiana)
The next seven slides can be used to stimulate discussion on the role of ecosystem surfaces in regulating the water cycle, runoff, and streamflow.
Rates of farmland conversion in the United States, the predominant type of land use change associated with built development. Soils, whether they are in forest, crop, or lawn or are exposed as bare earth in the image to the left, are pervious at a rate known as the infiltration capacity of the soil. The roofs, sidewalks, driveways, and roads in built development are impervious and do not absorb water.
* Data are from American Farmland Trust

12. Impact of land use change to built development on the hydrologic budget. With increased percentage of impervious surface (roofs, sidewalks, driveways, and roads), the percent of rainfall converted to runoff increases.
From Stream Corridor Restoration: Principles, Processes, and Practices, 10/98, by the Federal Interagency Stream Restoration Working Group (FISRWG). No copyright is claimed for this image.
from Stream Corridor Restoration, produced by the Federal
Interagency Stream Restoration Working Group

13. Infiltration Capacity
Watershed System ET
Infiltration Capacity
Soil
Erosion
Impervious
Cover
Vegetation
Density - +
Precipitation
Runoff
This slide illustrates how that might look from a systems perspective. In this unit, we are considering impervious cover. The relation between impervious cover and infiltration capacity is negative. An increase in impervious cover would cause less infiltration capacity, lower vegetation density by default (covered over), and causing soil erosion downslope in the watershed due to greater runoff. Within the watershed, water stored as soil moisture is less and, at the watershed outlet, runoff would increase.
Soil Moisture or Groundwater
Input
Storage (or Stock)
Output

14. Infiltration Capacity
Watershed System ET
Infiltration Capacity
Soil
Erosion
Impervious
Cover
Vegetation
Density - +
Runoff
Precipitation
Within the watershed, water stored as soil moisture is less and, at the watershed outlet, runoff would increase. Why is the loss of storage within the watershed critical? Is soil moisture important as a stock for us? Do we use it actively? Passively? How is groundwater related to this? What are the problems with greater watershed runoff?
Soil Moisture or Groundwater
Input
Storage (or Stock)
Output

15. The stream hydrograph is one way of considering the impact of development on ecosystem services. If this represents the hydrograph from a watershed dominated by pervious surfaces, the next slide shows the impact of development and its impervious surfaces.
Streamflow—general term used to describe water flow within a stream channel. It can refer to stage, a relative depth of water at a gaging station, or discharge (defined below). Streamflow is composed of both stormflow and baseflow.
Discharge—volume of water, or streamflow, that passes a given location in a channel within a given period of time. Discharge is expressed in cubic feet per second (cfs) or cubic meters per second (cms). Runoff is calculated from discharge.
Streamflow Hydrograph—literally a graph of water data related to streamflow, either stage or discharge, over time. The shape of a hydrograph (e.g., peakedness or flashiness) is dependent on watershed properties. Key characteristics of a streamflow hydrograph are illustrated in Figure 3.
Baseflow—the groundwater contribution to streamflow. It is a significant part of the streamflow hydrograph in wet climates. If present, it is generally more regular or constant than stormflow.
Stormflow—the stormwater contribution to streamflow. Stormflow occurs in response to a rainfall event and represents the direct runoff in response to the event. It generally increases with development in a watershed.
Peak Discharge—the point on the hydrograph where discharge is greatest. In small watersheds, it generally occurs immediately following the end of rainfall. Peak discharge depends on the direct runoff and the time it takes for the runoff to concentrate in the stream. It tends to increase with development in the watershed.
Time to Peak Discharge—time from the start of rainfall to peak discharge. It tends to decrease with development in the watershed.

16. Impact of land use change on a stormflow hydrograph, including total discharge (Qt), peak discharge (Qp), time of rise (Tr), and the time to peak from the centroid of the storm (Lag). With increased runoff produced by impervious surfaces associated with urbanization, more runoff produces greater total stormflow discharge and greater peak discharge. The time to peak decreases as the stream becomes more flashy, more prone to flash flooding. Because less rainfall percolates deeply, recharging groundwater, baseflow may actually decrease.
Peak Discharge—the point on the hydrograph where discharge is greatest. In small watersheds, it generally occurs immediately following the end of rainfall. Peak discharge depends on the direct runoff and the time it takes for the runoff to concentrate in the stream. It tends to increase with development in the watershed.
Time to Peak Discharge—time from the start of rainfall to peak discharge. It tends to decrease with development in the watershed.
What ecosystem services have been impacted? From the services included in the Ecosystem Services Fact Sheet (from the Ecological Society of America), those that directly impacted and affect the streamflow hydrograph include the ability of pervious surfaces to mitigate drought and floods by infiltrating water, some of which percolates deeply into groundwater and supports baseflow, and to protect stream and river channels from erosion due to higher peak discharge.