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
Radar data is used to create rainfall time series
for each subcatchment
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)
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 from red (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