Modeling the Effects of Terracing and Nonfederal Reservoirs on Water Supplies in the Republican Rive

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Modeling the Effects of Terracing and Nonfederal
Reservoirs on Water Supplies in the Republican
River Basin

• Ayse Irmak (University of Nebraska-Lincoln)
• Derrel L. Martin (University of Nebraska-Lincoln)
• James K. Koelliker (Kansas State University)

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Background

• A provision in the settlement of the litigation
  on the Republican River requires a study to
  determine the impact of field terraces and
  non-federal reservoirs on streamflow depletion.
• An early assessment of the amount of land
  terraced was developed by the USDA-NRCS.
• Surveys have also been conducted which highlights
  some characteristics helpful in designing the
  study
• Approximately two million acres have been served
  by terraces which represents more than 15 of the
  Republican River Basin above the Hardy gage
• Most of the terraced land is located in the
  central portion of the basin (e.g. less than 10
  of the land served by terraces is in Colorado)
• Most of the small reservoirs are located in the
  eastern half of the Nebraska portion of the basin
  and in the Kansas portion of the basin with few
  structures in Colorado.

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Background

• Terraces can be designed to serve several
  purposes.
• Reduce the rate of overland flow from the treated
  land which reduces erosion and sediment transport
  to waterways.
• Retain water for short periods in the channel.
  This type of terrace often has a piped outlet to
  drain water from the terrace channel.
• Conservation terraces were designed to retain
  significant amounts of water in the channel

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The type of terraces across the Republican River
Basin (RRB)

• Terraces with piped outlets that detain water for
  short periods are most common in the eastern
  portion of the basin where rainfall is more
  substantial.
• The main function of this terrace is to decrease
  erosion by shortening the slope length and by
  temporarily detaining runoff in the channel.
• Water is often discharged into grassed waterways
  that are less erosive than field conditions.
• Closed-ended terraces with level channels are
  more common in the central and western portions
  of the watershed.
• Conservation terraces are expected to have a more
  substantial effect on streamflow depletion
  because they retain substantial portions of the
  runoff from a storm and provide for either
  increased groundwater recharge or larger
  evapotranspiration amounts.

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Cross sectional view of terraced land
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Objectives

• To estimate the effects of terrace systems in
  agricultural hydrology using a water budget
  simulation model. In particularly, we are
  interested in the effects of terraces on
  streamflow and recharge in Republican River Basin
• Assessing the impact of terraces must include
  estimates of the rate of infiltration of water in
  the terrace channel and on the contributing slope
  portion of the inter-terrace area.

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Potential Yield (POTYLDR)Model

• Developed for Bureau of Reclamation (1984).
  Assess the effects of land use and conservation
  practices on large watersheds (Koelliker 1994 and
  1998)
• Estimates the water yield on a monthly or annual
  basis for a drainage area. Up to 18 different
  land use combinations can be simulated in one
  run.
• The model was developed for High Plains
  conditions and includes the range of land uses
  found in the Republican River Basin.
• Major components of POTYLDR model are
  Evapotranspiration Transpiration Interception
  Runoff Snow Soil water evaporation,
  infiltration and redistribution Land use and
  Pond.
• Runoff Curve numbers used to partition daily
  precipitation between runoff and infiltration.
  The method can predict runoff over a period of
  time provided the moisture condition at the time
  of each storm can be determined.

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Schematic of POTYLDR Water -budget model
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Illustration of representative hydrologic
response units for simulation of a portion of a
subwatershed using the POTYLDR model

• The model does not attempt to distribute crops
  and field conditions to individual land holdings.
  
• Simulates conditions for typical cropping, soil
  and other conditions as representative hydrologic
  response units (HRU).
• The representative HRU provide the water balance
  for a typical field in a portion of the
  subwatershed.
• The total contribution from similar lands in the
  subwatershed is computed by scaling up the
  results for one field to the amount of land for
  the respective land use.

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Water balance measurements in the contributing
slope area and the channel of the terraced field
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Major subbasins in the Republican River Basin
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Watersheds in Medicine Creek
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Soil distribution (SURGO)
Digitized terraced land
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Anderson Level II Landuse classification
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Temporal harvested acreage estimation of selected
crops in Frontier County, NE (NASS)
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Temporal harvested acreage estimation of selected
crops in Lincoln County, NE
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Soil moisture properties for soil classes derived
from SSURGO database
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Characteristics of Hydrologic Response Unit
simulations
YYes NNo GGood FFair
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Weather inputs

• Daily values of maximum and minimum temperature,
  precipitation
• Long term monthly average vales of relative
  humidity, wind speed, solar radiation, and
  percentage of possible sunshine
• Potential evapotranspiration (PET) is calculated
  by the combined energy budget and mass transfer
  by Penman (1948) and later modified by Jensen et
  al. (1971).
• The AET for various crops calculated by
  Blaney-Criddle method
• AET PET x k x Ks
• where Ks soil moisture adjustment factor
• k crop coefficient

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RESULTS
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AVERAGE ANNUAL WATER BUDGET FOR WHEAT-FALLOW
ROTATION IN MEDICINE CREEKAverage annual lake
evaporation 51.12 inchesAverage annual
precipitation 20.52 inches Weather station
CurtisSimulation are from 1950 through 2000Silt
loam. Hydrologic group B/C. Curve numbers for AMC
I, II, III 53, 72, 86Curve numbers for fallow
62, 79, 91Planting 10/01 and Harvest 6/25
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RUNOFF INTENSITY FOR WHEAT-FALLOWROTATION IN
MEDICINE CREEK (Average annual precipitation
20.52 Inches) (Curtis, 1950-2000)

• INTENSITY FREQUENCY
• (IN.) ( ) (DAYS)
• gt0.0 100.00 477.00
• gt0.1 28.09 134.00
• gt0.2 14.47 69.00
• gt0.3 11.32 54.00
• gt0.4 7.97 38.00
• gt0.5 6.29 30.00
• gt0.6 4.82 23.00
• gt0.7 3.56 17.00
• gt0.8 2.94 14.00
• gt0.9 2.10 10.00
• gt1.0 1.89 9.00
• gt1.1 1.68 8.00
• gt1.2 1.68 8.00
• gt1.3 1.26 6.00
• gt1.4 1.05 5.00
• gt1.5 1.05 5.00

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AVERAGE ANNUAL BUDGET FOR CONTINOUS CORN in
MEDICINE CREEKAverage annual lake evaporation
51.12 inchesAverage annual precipitation 20.52
inches Weather station Curtis. Simulations
1950-2000 Silt loam. Hydrologic group B/C. Curve
numbers for AMC I, II, III 57, 75, 88 Planting
05/03 and Harvest 10/11
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RUNOFF INTENSITY FOR CONTINOUS CORNIN MEDICINE
CREEK (Average annual precipitation 20.52
Inches) (CURTIS, 1950-2000)

• INTENSITY FREQUENCY
• (IN.) ( ) (DAYS)
• gt0.0 100.00 484.00
• gt0.1 32.85 159.00
• gt0.2 17.98 87.00
• gt0.3 13.22 64.00
• gt0.4 9.71 47.00
• gt0.5 6.20 30.00
• gt0.6 5.58 27.00
• gt0.7 4.13 20.00
• gt0.8 2.69 13.00
• gt0.9 2.48 12.00
• gt1.0 1.45 7.00
• gt1.1 1.45 7.00
• gt1.2 1.24 6.00
• gt1.3 1.24 6.00
• gt1.4 1.03 5.00
• gt1.5 0.83 4.00

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CONCLUSIONS

• We are in the process of POTYLDR model
  development.
• Improvement of water balance model
• Functions and subroutines from CROPSIM AND SWAT
• ET
• Use of SURGO database/Layering of soil profile
• Transmission losses of streamflow during events
• ARCGIS User-Interface
• We installed equipment in terraced lands in
  Nebraska and Kansas. Data will be used to
  describe the impact of terraces and small
  reservoirs on streamflow and recharge.

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CONCLUSIONS

• We assumed that runoff from upslope will all
  enter the bottom section. Terrace channels can be
  overtopped if the amount of runoff from the
  contributing slope area exceeds the storage
  volume of the channel
• Terraces are typically designed to store the
  runoff volume for a 10-year storm of 24-hour
  duration. Our 50-year results showed that there
  was NOT significant intensity of runoff from the
  contributing slope area during the simulation
  period to cause overtopping or loss of runoff.
• It was estimated that on average 1.3 inches of
  water could be retained in terrace lands for the
  wheat-fallow rotation due to increased
  percolation in the channel. This is a significant
  amount of number compared to non-terraced land.
  The impact of terracing is larger especially in
  years where there is a significant amount of
  rainfall. We believe that terraced land will
  increase consumptive water use for plants,
  increased ET which will result in increased crop
  yields.