p3 ivil Engineering Erehwon Basin The hypothetical drainage basin that is the subject of this study is located in mid-Am

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p3
ivil Engineering
Erehwon Basin
The hypothetical drainage basin that is the subject of this study
is located in mid-America. Precipitation, surface runoff,
evapotranspiration, and groundwater levels have been
measured for several years and provide the basic data to derive the
water budget. The basin is 247 square kilometers in area and the
land in the basin slopes gently from
surrounding hills at the edges of the basin toward a single stream
- Jhed Creek - that originates in the basin and flows out of the
basin. There is no surface-water or
groundwater flow into the basin from outside (i.e., Qis = Qig =
0.000 cubic meters per second [m3/s].) No groundwater is added to
or removed from the basin via wells or other
man-made facilities.
Water-Budget Components
Precipitation (P) is in the form of rain and snow. Based on 20
years of measurements, the months of greatest precipitation are
April, May, and June, and the least precipitation
occurs in December, January, and February. Averaging the annual
precipitation provides a value of 1.10 m, evenly distributed over
the basin.
Surface Runoff, Groundwater Discharge to Streams, and Groundwater
Flow Out of the Basin
Surface runoff (which you can also call stream flow or stream
discharge) (Qos) was measured at a point on Jhed Creek where it
leaves the basin and enters a large river.
The flow at this point varied – more flow occurred in winter and
spring than in summer and fall – but averaged 5.33 m3/s. Note that
this value includes overland flow into the
creek (for which there is no symbol or separate value) and
discharge from the groundwater system into the creek (baseflow, or
Qg.)
Using continuous measurements of stream flow, average groundwater
discharge from the groundwater system in the basin into Jhed Creek
(Qg) was estimated at 1.57 m3/s.
Groundwater outflow from the basin (Qog) was estimated at 1.45
m3/s. Note that the term “groundwater outflow” (Qog) refers only to
water that flows out of the basin as
groundwater and does not include the water discharged from the
groundwater system to Jhed Creek (Qg.)
Evapotranspiration
Based on 20 years of measurements, the months of greatest
evapotranspiration are July, August, and September. Using methods
provided by the National Weather Service,
average annual evapotranspiration from the surface (Es) of the
basin was estimated to be an equivalent of 0.427 m while average
annual evapotranspiration from the groundwater system (Eg) was
estimated to be an equivalent of 0.0550 m.
Changes in Storage
Using instruments to measure water levels in streams and wells, the
following estimates of average annual change in water storage were
made:
 Surface water (ΔSs) = 0.000 m
 Groundwater: (ΔSg) = -0.274 m

Determining Recharge
Your first task for this assignment is to estimate the average
annual recharge to the groundwater system (I). You need to create
this estimate two different ways – one using
the surface-water budget and one using the groundwater budget – so
that you can compare the results. Prepare a spreadsheet to organize
the available data and perform
the calculations, and include this spreadsheet in your assignment
deliverable. I also suggest you use the diagrams for surface-water
and groundwater budgets provided in
Lecture 1-B to organize your approach and keep track of the data.
Note the slight difference in notation for some components noted in
the diagrams and used in this
assignment; for example, the groundwater discharge out of the basin
is noted in the groundwater diagram as Qo and in this assignment as
Qog to distinguish it from the
surface runoff out of the basin Qos. You may even want to draw a
schematic map of the basin to use to illustrate your budget.
Make it clear what value(s) of recharge you obtained. Please use
only m3/y or m throughout the assignment calculations and use only
units of m/y for your final
answer. Please provide a description of how you approached
determining the recharge, including all assumptions you made (and
there will be some) and show all your work. Submit your description
and solution as a Word document and your supporting calculations as
an Excel document.
Uncertainty in Values of Selected Components
Your second task for this assignment is to use the information
in your text and additional research using outside sources to
evaluate and describe the level of uncertainty associated with
measured or estimated values of the following components of the
water budget: precipitation, evapotranspiration, and surface
runoff. Be sure to defend your response and include citations for
any references you used. Add your response to the same paper
required for the first task in this module. Finally, offer
defensible reasons for any differences between the recharge values
obtained by using the surface-water budget and the groundwater
budget.