Streams in urbanizing landscapes: from syndrome diagnosis to watershed prescription NSF Grant

Urban Streams: Examples of How Secondary Mathematics is used in Scientific Research JULIE GRAVES NCSSM TCM CONFERENCE JANUARY 2015

The Water Cycle in an Undeveloped Watershed

The Water Cycle in a Developed Watershed

Moving Water Water travels downhill from points of higher energy to point of lower energy, unless forced to do otherwise, until it reaches a point of equilibrium, such as a large lake or an ocean. This travel is facilitated by the presence of natural conveyance channels such as brooks, streams and rivers. The water’s journey may also be aided by man- made structures such as drainage swales, pipes, culverts and canals.

How do urban watersheds differ from undeveloped watersheds? Urban stream photo

Impervious Surfaces As watersheds are urbanized, much of the vegetation is replaced by impervious surfaces, thus reducing the area where infiltration to ground water can occur.

The presence of more impervious surfaces means that more storm water runoff occurs. This runoff must be collected by man-made drainage systems that combine curbs, storm sewers, and ditches to carry storm water runoff directly to streams.

In a developed watershed, much more water arrives into a stream much more quickly. The result is an increased likelihood of more frequent and more severe flooding.

Urban Stream Syndrome  Higher peak flows  Channel erosion  Increased pollutant concentrations  Loss of sensitive organisms

Development Intensity and Hydrographs Hydrographs for urban stream and natural streams are very different and present different sets of consequences for the environment. It is well understood that the percent of impervious cover in a watershed is an important explanatory variable. More impervious cover is associated with “flashier” hydrographs, higher concentrations of downstream pollutants and more downstream erosion.

Research Goals The status quo in watershed management has been to control the amount of impervious surface area. This approach does not take into account the fact that there are other aspects of development that could be the cause of adverse ecological impacts. It could be that the real drivers of the “urban stream syndrome” are other variables, including  storm water infrastructure (density of pipes),  road density  the configuration of impervious cover, The key to reducing harmful ecological outcomes may be to control these other factors.

Research Goals Researchers hope to understand the relationship between the pattern or configuration of development and the ecological consequences (habitat loss, pollution). If they succeed, it will be possible to manage watersheds so that a given level of development intensity can have a smaller impact on the health of urban streams.

Configuration of Development Here are USGS maps of several watersheds in North Carolina that are being studied. The watersheds have roughly equal areas and have comparable impervious cover percentages. The differences are in other characteristics that are being investigated as explanatory variables.

Explanatory Variables that quantify “configuration of development” % Developed in watershed % impervious Surface Area % forest Pipe densityMeters/square km Inlet DensityMeters/square km Road DensityMeters/square km Stream DensityMeters/square km Number of PatchesFRAGSTAT Mean Patch AreaFRAGSTAT ClumpinessFRAGSTAT Correlation LengthFRAGSTAT

Response Variables Flooding: as represented by a hydrograph that shows discharge over time Contaminant Loading: as measured by concentration of chemicals in streams

Secondary Mathematics at Work (1) Measuring Discharge (2) Using Stage to Predict Discharge (3) Regression and correlation for relationships between explanatory and response variables

Measuring Discharge

Calculating Discharge

Measuring Stage

Data Analysis at Work  Discharge, or flow, is measured in cubic meters per second  Discharge is expensive and time consuming to measure, though it can be done  Stage (depth) is much easier and cheaper to measure  Stage and discharge are closely related; a graph that shows this relationship is called a stage-discharge rating curve  A measurement of stage, together with a rating curve, makes it possible to calculate discharge without having to directly measure it.

Stage Discharge Rating Curve

Stage-Discharge Rating Curve

Rating Curve Q = discharge (cubic meters per second) h = measured water level (meters) a = water level corresponding to Q=0 c = coefficient that quantifies the particular characteristics of a stream channel

Rating Curve Calculations Based on measured data that provides a value for a, and that gives values of h and Q that occur together, we can do linear regression to ordered pairs in which one coordinate is log(h+a) and the other coordinate is log(Q). The slope of the resulting regression line will be the value of b and the intercept of the line will be log(c).

Real-time Data USGS provides an abundance of real time and historical data. Go to for information about rivers anywhere in the country

Stage and Discharge Data for Eno River Hillsborough NC January 2013 February 2013 March 2013April 2013May 2013June 2013 Discharge (cubic feet/sec) Stage (feet) Missing data2.026 July 2013August 2013September 2013 October 2013 November 2013December 2013 Discharge (cubic feet/sec) Stage (feet)

Preliminary Results

Conclusion To manage urban watersheds more effectively, we need to understand how to separate effects of development intensity from development pattern. Ongoing urbanization will make us unable to actually reduce impervious surface cover. Therefore, we would like to learn if we can manage the configuration of development and its associated infrastructure. If we can, we may be able to mitigate the effects of developed surface area.

What are researchers interested in? Paved parking lot photo Parking lot with vegetation photo

Thank You