GEO3280 Group Project Page | 29
University of Florida
Department of Geography
GEO 3280
Group Project
Estimating the Hydrologic Regime at Ungauged Points in the Basin
INTRODUCTION: As stated at the outset of the manual, water resources are extremely important to all countries, and will be increasingly so as population rises. Many nations neither have the time or financial ability to fully monitor their water resources, yet they must make crucial decisions about the allocation of water resources for various, often competing, uses, employing limited financial resources. This final assignment illustrates the value of the preceding exercises in furnishing estimates of components of the water budget within the Tiribí basin. Estimates may be required for a variety of hydrologic projects including an “environmentally friendly” run-of-river hydro-electric power plant, an agricultural irrigation scheme, the location of a new intake to supplement municipal water supplies, a new sewage treatment plant, or a coffee processing plant. It could even be something as unusual as the evaluation of a site for potential use in eco-tourism, perhaps supporting white-water rafting throughout the tourist season, which of course is when the sun shines, the rains stay away and it is winter in “Gringo-land” (the dry season November-March)!
Costa Rica obtains some of its hydro-electric power from small, “run-of-river”, generating plants which have no large, and environmentally contentious, reservoirs to sustain the flow of water (and electricity!) through the year. The efficiency of these plants is therefore very dependent upon the accurate estimation of the annual flow regime of the river at any potential installation location. However, there are no historic streamflow records within the Tiribí basin above Electriona, so our accumulated knowledge of hydrology must be used to estimate one.
Selecting a study site and project group:
5 potential sites have been identified within the basin (Figure 8.1), corresponding to the major tributaries of the Tiribí, and are all of roughly the same area. Each drains a hydrologically different area. Several of the assignments required time series of various hydrologic variables to be estimated at “representative cells” within each, to provide an overall appreciation of this geographic variability. The Río Cañas (1) and Río Jorco (2) drain the northern flanks of the Cordillera Talamanca. The Río Chiquito (3) and Río Tiribí, near Tres Ríos (4), drain the western flank of the Cordillera Central, while the Río María Aguilar (5) drains the more urban area around, and to the east of, metropolitan San José.
At this point each of you is allocated to one of 5 groups, roughly equal in membership. Rather than have each of you evaluate all 5 potential sites, the task of evaluating one site will be assigned to each group as follows:
Group Potential Site UFID ends in
1 Cañas 0 or 1
2 Jorco 2 or 3
3 Chiquito 4 or 5
4 Tiribí (Tres Ríos) 6 or 7
5 María Aguilar 8 or 9
THE ICON INDICATES THE BARE MINIMUM INFORMATION THAT I WISH TO SEE IN YOUR FINAL REPORTS AND PRESENTATIONS. I HOPE THAT YOU WILL HAVE MORE THAT YOU WISH TO ADD.
A. How Can the Limits of The New Sub-basin be Established from the Digital Elevation Model?
The streamflow regime at these points is a function of the water budget of all the cells which contribute water to them. The first step is therefore to identify all contributing cells “upstream” of these points. Surface water flows downhill, and is assumed to flow down the steepest gradient. The Digital Elevation Model provides the average elevation in each cell and also in the 8 cells surrounding it (Figure 8.2). This and the distance to the centers of adjacent cells permits the computer to define the steepest slope “out” of a cell, which then determines the direction in which water will flow from that particular cell.
One of the eight possible “compass directions” (Figure 8.2) is then associated with each cell. The letters “NW” or “S” are inefficient for the computer to work with, instead each of the eight directs is assigned a numerical value, as shown in the lower portion of Figure 8.2. The number stored inside each cell therefore indicates the direction in which water exits that cell. For example, a cell with a number “1" in it indicates that water would move out of the cell to the “East” or to the cell immediately to its right, whereas a cell containing the number “32" would export its water to the “Northwest”, or to the cell diagonally above it and to its left.
q 1. For the sake of practice before working with the flow directions in your own sub-basin:
- Draw the flow directions joining cells on the imaginary basin defined in the Figure 8.3, whose outflow is located at cell [1,4]. The number “16" indicates that the water flows from this cell to the “west”, out of the matrix.
ii. Shade in all cells whose runoff/storage would contribute to flow at this outflow point.
iii. The remainder of the large matrix is occupied by 5 other drainage basins of varying sizes (one is only occupies a single cell). Identify the limits of these remaining five sub-basins.
iv. Mark clearly the location of the outlets of each of the 5 sub-basins, indicating the direction in which the outflow is exiting from the outflow points.
(8 Marks)
q 2. Locate your designated potential site on Figure 8.4. Search for the cell or cells (because several cells may contribute to a single cell) amongst the site’s immediate neighbors, which flow into this cell. For each contributing cell, repeat this process until no further cells flow into the cells that you identified previously. This is the equivalent to working one’s way back up a stream network. Construct, and submit, the outline of your sub-basin and the fully connected flow network contributing to your particular potential site.
(4 Marks)
q 3. Create a new outline worksheet for your sub-basin, using “1"s for the potential site and all cells which contribute to it, and “0"s for all other cells. Provide a printout of the revised “sub-basin limits” spreadsheet showing a “map” of the sub-basin within the Tiribí basin, similar to the “basin limits” one used throughout the assignments.
(1 Mark).
R Hint: This process can be facilitated by making a copy of your “Basin Limits” file (for the entire Tiribí above Electriona, and replacing the requisite areas of “1"s which do not fall into your sub-basin, with “0"s. Save the new file as “Sub-Basin Limits”.
B. What Sort of Hydrologically Important Data Should be Extracted from the Available Data?
Take your newly created SUB-BASIN LIMITS file and apply it to the TIRIBIELEV and LANDUSE files in turn, in order to identify only those portions of the larger Tiribí basin that are relevant to the sub-basin.
q 1. Create a 3-D plot of the topography of your sub-basin
(3 Marks)
!Setting: Minimum 900, Maximum 2700, Increment 100, regardless of bounds of your sub-basin, in order that your output is comparable to that of the entire basin. Identify “north” on your maps?
q 2. In the original representation of the Tiribí basin, the 302.4 km2 basin area is represented by the grid cells within BASINLIMITS. Using this relationship compute the basin area of your new basin in km2.
(1 Mark)
q 3. Construct a hypsometric curve of your sub-basin and place it on the same graph as the hypsometric curve for the entire Tiribí calculated in Assignment 1. Estimate and submit values of the medians, quartiles and inter-quartile ranges of the overall basin and your sub-basin based on the structure of table 8.1.
(4 Marks)
Tiribí atElectriona / Sub-basin / Difference
Median (m)
Lower quartile (m)
Upper quartile (m)
Inter-quartile Range (m)
Table 8.1. Tabular comparison of topographic characteristics of sub-basin and the Tiribí at Electriona.
q 4. Assign a particular background color to each cell dependent upon the land use category allocated to it, and print out a “land use map” of your basin.
(1 Mark)
q 5. Create a histogram of the percentage of total sub-basin that each type of land use occupies in your sub-basin. Create a figure for your sub-basin equivalent to the land-use data per 250m elevation band, shown in Figure 5.19. Does your sub-basin contain more or less of each landuse type than the basin as a whole? Figures for the entire basin are provided in the file “Land Use by Elevational Band”
(2 Marks)
q 6. In no more than half a page, discuss the similarities and differences in topography and land use between your sub-basin and the Tiribí as a whole, referring to the maps, tables and graphs constructed above. Specifically, what consequences might these characteristics have on 1) Precipitation, 2) Interception, 3) Temperatures and 4) Evapo-transpiration in your sub-basin?
(2 Marks)
Coordinate Potential Name of sub-basin
Site of Outflow
O ,16 Cañas
P ,16 Jorco
AA ,12 Chiquito
Z ,12 Tiribí (Tres Ríos)
K ,10 María Aguilar
C. Can Expected Monthly Flows in Your Sub-basin be Generated Using the Flow Chart ?
Open each of the existing monthly worksheets. Replace the Tiribí outline worksheet “Basin Limits” (containing 0s and 1s to define the limits of the entire Tiribí basin), with the new outline file you have for your particular forecast basin, “Sub-Basin Limits”.
! Warning: Once you have inserted the new sub-basin limits, save each monthly spreadsheet under a new file name, using “file save as”. I recommend that you simply add on the name of your forecast basin, i.e. if dealing with the September spreadsheet, once new basin outline has been substituted, save this immediately as “September Jorco” (or, Chiquito, Aguilar, etc.). Just take care not to erase the original “September” file. If erased by accident, all is not lost, simply grab a Tiribí outline from another month and paste it into the requisite monthly worksheet.
1. q Tables 8.1 to 8.5 contain incomplete water balance information for the five potential sites. Only those missing monthly and annual information for precipitation, interception, effective precipitation, evaporation and excess precipitation for your designated basin need be submitted. Fill data to one decimal place.
(5 Marks)
2. q Following the flowchart from the previous assignment, reproduced in Figure 8.5, and the same four initial values of the parameters:
Proportion of direct runoff: 0.05
Storage Capacity (mm): 563 mm
Initial Storage (mm): 222 mm
Storage Recession constant 0.21
compute the values of mean monthly runoff for your sub-basin, and add to the appropriate Table (8.1 to 8.5).
(12 Marks)
ü Check: The first monthly values (May) of runoff for each of the five sites are as follows:
Cañas 84.5 mm
Chiquito 92.2 mm
Jorco 81.8 mm
María Aguilar 85.9 mm
Tres Ríos 91.0 mm
3. q Compute monthly storage as a residual term from Tables 8.1 to 8.5, as appropriate, and tabulate cumulative storage. Compute annual totals of each variable. Compute your annual storage as a percentage of annual precipitation input.
(2 Marks)
q SUBMIT A COMPLETED VERSION OF YOUR SUB-BASIN TABLE.
R Note: Do not use the storages used in your computations of runoff, calculate storage as [Excess Precipitation - Runoff]. Ensure that you calculate an annual total of monthly values of each variable, not an average of the 12 monthly values.
q 4. Produce times series (X-Y scatters with connecting lines) of the 12 monthly values of:
Precipitation
Excess Precipitation
Evaporation
Runoff
Storage
at your test site, on the same graph using identical vertical scales. Months will consistently be the x-axis and the hydro-meteorologic variables will constitute the y-axis.
(5 Marks)
q 5. Convert your values of monthly runoff (mm) to units of discharge (m3s-1). Graph your forecasted mean monthly discharge hydrograph.
(2 Marks)
ü Check: All monthly discharges (m3s-1) should be in single digits. Values may be extremely low at the end of the dry season.
DEFINITION OF TERMS USED IN FLOWCHART:
ISTORE Initial soil/groundwater storage at the start of each month (Initial value: 222mm)
M Month under evaluation (1, 2, ....., 12)
XS Excess Rainfall - [Precipitation-Interception-Evaporation] (mm)
DIRQ Direct Runoff (mm)
DIRATE Proportion of excess rainfall going to Direct Runoff. (Initial value: 0.05)
STORE Temporary calculation of water stored in the Soil/Groundwater system (mm)
WHC Maximum storage capacity of the Soil/Groundwater system (mm) (Initial value: 563 mm)
SATXQ Saturation Excess Runoff (mm)
SUBQ Subsurface Runoff (mm)
K Soil/Groundwater Recession Rate (Initial value: 0.21)
RUNOFF(M) Total Runoff computed for month, M, (mm).
STORE(M) Water stored in the Soil/Groundwater system at the end of month, M, (mm)
Figure 8.5. Flowchart by which values of monthly runoff may be calculated from values of monthly excess rainfall.
GEO3280 Group Project Page | 29
Table 8.2. Incomplete mean monthly estimates of the hydrologic budget for the Chiquito sub-basin
CHIQUITO
J / F / M / A / M / J / J / A / S / O / N / D / AnnPrecip / 51.8 / 21.0 / 49.7 / 304.8 / 251.3 / 440.0 / 256.5
Intrcp / 8.8 / 3.8 / 9.3 / 54.9 / 45.1 / 87.8 / 45.2
Eff P / 43.0 / 17.2 / 40.4 / 249.9 / 206.2 / 352.1 / 211.3
Evap. / 41.5 / 44.4 / 51.9 / 67.3 / 72.8 / 74.2 / 52.1
XS Pre / 1.5 / -27.2 / -11.5 / 182.6 / 133.4 / 278.0 / 159.2
Runoff
Store
Cum S
Table 8.3 Incomplete mean monthly estimates of the hydrologic budget for the Tiribí near Tres Ríos sub-basin
TRES RÍOS
J / F / M / A / M / J / J / A / S / O / N / D / AnnPrecip / 48.2 / 20.6 / 50.6 / 299.7 / 246.3 / 431.7 / 246.7
Intrcp / 8.3 / 3.7 / 9.2 / 53.4 / 43.8 / 85.4 / 43.4
Eff P / 39.9 / 16.9 / 41.4 / 246.3 / 202.5 / 346.3 / 203.4
Evap. / 43.7 / 46.8 / 54.0 / 68.3 / 73.5 / 74.2 / 53.6
XS Pre / -3.8 / -29.9 / -12.6 / 178.0 / 129.3 / 272.1 / 149.8
Runoff
Store
Cum S
Table 8.4 Incomplete mean monthly estimates of the hydrologic budget for the María Aguilar sub-basin
MARÍA AGUILAR
J / F / M / A / M / J / J / A / S / O / N / D / AnnPrecip / 15.8 / 16.9 / 58.7 / 254.2 / 202.1 / 357.5 / 159.4
Intrcp / 1.3 / 1.2 / 3.8 / 17.3 / 13.8 / 27.1 / 11.3
Eff P / 14.5 / 15.7 / 54.9 / 236.9 / 188.3 / 330.4 / 148.1
Evap. / 67.1 / 72.6 / 76.3 / 79.5 / 78.7 / 75.7 / 68.9
XS Pre / -52.6 / -56.9 / -21.4 / 157.4 / 109.6 / 254.7 / 79.2
Runoff
Store
Cum S
Table 8.5. Incomplete mean monthly estimates of the hydrologic budget for the Cañas sub-basin