The hydrograph for Ten Mile Creek is shown to the right.

1. SMALL SUB-CATCHMENT DELINEATION AND RAINFALL RUNOFF MODELING FOR BASINS Upper Iowa River Catchment By Eric Hudson Faculty Advisor: Richard Bernatz The objective of this research project is to determine the volume flow rate (cubic feet per second) of the Upper Iowa river due to rainfall runoff. Flow calculations are based On the TOPModel concept wherein square elements of the river catchment are grouped according to hydrologic and physical characteristics. The flow modeling is intended to assist in the study of land use effect on flood frequency and severity, as well as solid and chemical transport within the catchment. TOPModel Flow Calculations Hydrologic Similarity Groups Elements of a given subcatchment are grouped according to their potential for reaching saturation.Each element is assigned an index based on hydrologic and physical characteristics. Like elements form a Hydrologic Similarity Group (HGS) Radar data is used to create rainfall time series for each subcatchment Catchment Delineation • The HSG index for a given element is based on : • The Uphill region draining through the element (Water exits an element following the greatest downhill slope to a surrounding node) • The greater the area draining through a given element, the greater its index. • The surface slope of the element. • The steeper the slope of an element, the lower its index. 1) The Digital Elevation Model (DEM) file of Northeast Iowa is a data set of elevations on a grid of 30 meter by 30 meters squares, or elements Rainfall time series is the primary input To the TOPModel rainfall runoff algorithm • Basic TOPModel Storage and Flow Variables: • S(t) = Average Saturation Deficit (Length) • = flow from the unsaturated zone to the saturated zone (Length/Time) • where i is the hydrologic similarity group (HSG) index, and is the percentage of subcatchment area associated with the HSG. • = flow from the saturated zone to the stream • where S(t-1) is the average subcatchment storage deficit from the previous time, and m is a parameter specifying the rate of decrease of transmissivity with increasing storage deficit. 2) Extraction – The rectangular area containing a given subcatchment is grabbed from the master DEM The range of HSG indices range fromred (high and dry) to blue (low and wet) on the ROYGBIV scale In this case we are extracting Ten Mile Creek 3) Fix – For each subcatchment the data must be altered to remove sinkholes Histogram of number of elements per HSG index 4) Trace – The extracted rectangular area contains elements not in the subcatchment. These are removed using our trace algorithm which identifies all elements whose rainfall will drain to the given inlet to the Upper Iowa river Elements with lower indices are less likely to be saturated. Element Conceptual Model for TOPModel At any given time, the ground is saturated for all elements with a HSG index above a certain value depending on the recent rainfall history. The hydrograph for Ten Mile Creek is shown to the right. Hydrographs are calculated for each of the 30 Subcatchments. A total of 30 subcatchments (18 stream subcatchments and 12 river basin catchments) were delineated for the Upper Iowa catchment upstream from Decorah • Typically, elements with an HSG index of 15-17 will be saturated under “normal” weather conditions. • However, excessive rainfall will cause elements with a HSG index as low as 12 to become saturated. • Extremely dry conditions may mean saturation occurs for elements with an HSG index of 19 or greater. Decorah, Iowa Saturated elements in Ten Mile Creek for level 15