NATURAL HYDROGRAPH Base flow separation technique Qb a

NATURAL HYDROGRAPH Base flow separation technique, Qb: a. Empirical formula b. Master depletion curve c. Simple straight lines Topic 4 EXPLAIN HYDROGRAPH ANALYSIS CONSTRUCT CALCULATE CONCEPT OF UNIT HYDROGRAPH Volume Of Direct Runoff From Direct Runoff Hydrograph. DETERMINE The Change Of Unit Hydrograph Duration Using: a. S-curve b. Superposition Concept.

HYDROGRAPH • A hydrograph is a graph showing the rate of flow (discharge) versus time past a specific point in a river, or other channel or conduit carrying flow. The rate of flow is typically expressed in cubic meters or cubic feet per second (cms or cfs).

DEFINITION OF NATURAL HYDROGRAPH • A natural hydrograph is one recorded at a stream gauging site and is a finger-print of the upstream drainage area’s response to rainfall

CONCEPT OF UNIT HYDROGRAPH • A Hydrograph is a graph showing changes in the discharge of river over a period of time. • It can also refer to a graph showing the volume of water reaching particular outfall or location in a sewerage network, graph are commonly used in the design of sewerage, more specillcally, the design of surface water sewegare systems and combination system.

A hydrograph consists of: a) A rising limb or concentration curve b) A peak or crest segment c) Falling limb or recession curve

• The properties or characteristics of a unit hydrograph are a) the volume under a unit hydrograph is equal to 1 unit (1 cm or 1 in) rainfall excess b) If the duration of two rainfall excess events is equal, without regard to their respective rainfall intensities, they must result in the same hydrograph time base. c) The unit hydrograph results in a linear system whereby the direct runoff for a storm of a specified duration is directly proportional to the rainfall excess amount or volume d) Rainfall distribution for all equal duration storms is identical in space and time.

Calculate direct runoff from stream flow & base flow data • Direct runoff = stream flow – base flow

Schedule below shows observation data from stream flow with base flow depth in catchment's area 250 km 2. from that data , get direct runoff magnitude. example Time (hour) Stream flow, Q (m 3/s) Base Flow, (m 3/s) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 1. 37 1. 25 1. 12 5. 00 12. 00 15. 60 17. 15 14. 40 8. 80 6. 80 5. 50 4. 10 2. 75 2. 00 1. 20 0. 65 0. 15 0. 32 0. 62 1. 25 1. 28 1. 35 1. 42 1. 65 1. 82 1. 88 2. 05 2. 55 1. 91 1. 53 1. 15 0. 28

Calculate Direct Runoff Depth Base On Volume DRO And Cathment Area. • DRO Depth, rd = Vd A DIMANA; Vd A Qn Δt = RUNOFF VOLUME = Qn Δt = CATCHMENT WIDE = HYDROGRAPH ORDINATE = HYDROGRAPH TIME INTERVAL

Calculate runoff volume and excess rain depth to a 7 acres catchment's area. Schedule below show a direct runoff data resultant from one precipitation EXAMPLE Time (minute) 0 2 4 6 8 10 Flow, Q (cfs) 0 0 9 21 17 13

Convert the duration of unit hydrograph from short to long (superposition)

Convert The Duration Of Unit Hydrograph From Short To Long (Superposition Method)- graphic The following are the ordinates of a 4 -hour unit hydrograph. Derive the ordinates of a 12 - hour unit hydrograph Time 4 hr-UH (Hour) (m 3/s) 0 0 4 3 8 33 12 96 16 63 20 35 24 25 28 12 32 6 36 3 Combined 4 hr-UH Lagged 4 hr-UH 12 hr-UH

Convert The Duration Of Unit Hydrograph From Short To Long (Superposition Method)- table Time 4 j-UH (Hour) (m 3/s) 0 0 4 3 0 8 33 3 12 96 16 Lagged (+) 4 j-UH 12 j-UH 0 0 3 1 0 36 12 33 3 132 44 63 96 33 192 64 20 35 63 96 194 64. 67 24 25 35 63 123 41 28 12 25 35 72 24 32 6 12 25 43 14. 33 36 3 6 12 21 7 3 6 9 3 3 3 1 40 44

Example : • The following are the ordinates of a 3 -hour unit hydrograph. Derive the ordinates of a 6 -hour unit hydrograph and plot the graph.

Solution

Time (Hour) 0 4 j-UH (m 3/s) 0 3 1. 5 6 (+) 4 j-UH 12 j-UH 0 0 0 2 0. 75 4. 5 1. 5 6 3. 00 9 8. 6 4. 5 13 6. 55 12 12. 0 8. 6 21 10. 30 15 9. 4 12. 0 21 10. 70 18 4. 6 9. 4 14 7. 00 21 2. 3 4. 6 7 3. 45 24 0. 8 2. 3 3 1. 55 27 0. 8 1 0. 40 30 Lagged

25 20 15 3 hr-UH lagged 3 hr-UH Combined 3 hr-UH 6 hr-UH 10 5 0 0 3 6 9 12 15 18 21 24 27

Question 1: • Determine the 4 hr-UH from the 2 hr-UH given in the table using the superposition principle method

Changing a Short Duration Unit Hydrograph to Long Duration using S -Curved method

Example • The ordinates of a 4 -hour unit hydrograph for a particular basin are given below. Determine the ordinates of the S -curve hydrograph and there from the ordinates of the 6 hour unit hydrograph

Solution Time 4 hr-UH (Hour) S- Curve Addition S- Curve Ordinates Lagged S- Curve difference 6 hr - UH 0 0 2 25 4 100 6 160 8 190 10 170 12 110 14 70 16 30 18 20 6 22 1. 5 24 0

Time (Hour) 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 4 hr-UH 0 25 100 160 190 170 110 70 30 20 6 1. 5 0 S- Curve Lagged S- Curve Addition Ordinates S- Curve difference 0 0 25 0 100 25 185 0 185 100 290 25 265 185 355 100 255 290 400 185 215 355 425 290 135 400 430 355 75 425 445 400 45 430 436 425 11 445 446. 5 430 16. 5 436 445 -9 446. 5 436 10. 5 436 446. 5 -10. 5 6 hr - UH 0. 00 16. 67 66. 67 123. 33 176. 67 170. 00 143. 33 90. 00 50. 00 30. 00 7. 33 11. 00 -6. 00 7. 00 -7. 00

Question 1 • Determine the 3 hr-UH from the 1 hr-UH given in the table using the S-curve method.

Time (Hour) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 3 hr-UH 0 66 134 266 534 466 400 334 266 200 134 66 0 0 0 S- Curve Lagged S S- Curve 1 hr - UH Addition Ordinates - Curve difference 0 0 0 66 0 66 198 134 66 68 204 0 266 134 132 396 66 600 266 334 1002 134 600 0 0 266 600 66 198 600 934 666 268 804 600 866 934 -68 -204 666 866 0 0 934 1068 866 202 606 866 932 1068 -136 -408 866 932 -66 -198 1068 866 202 606 932 1068 -136 -408 Changing a Long Duration Unit Hydrograph to Short Duration using S-Curved method

Question • The following are the ordinates of a 4 hr – UH. Derive the ordinates of a 3 hr-UH

Derive the S-curve for 4 hr-UH

Hydrograph Unit from Stream Discharge Data

Example • Table below show runoff from hydrograph data, for a 50 km 2 catchment. Calculate the unit hydrograph (UH)10 mm. Assume that the basic flow is 5. 0 m 3/s

Solution

Mendapatkan Hidrograf Jumlah • Penggunaan UH 10 bagi kawasan tadahan yang sama dengan contoh 1. • Diberikan ribut yang lain dengan tempoh yang sama bagi kawasan tadahan yang sama iaitu 50 km 2. Anggapkan aliran dasar 7 m 3/s

Latihan • Cerapan kadaralir bagi satu kejadian hujan berkesan 12 jam bagi kawasan seluas 1150 km 2 adalah seperti yang ditunjukkan. Dapatkan hidrograf unit (UH)10 mm untuk kawasan ini.

• Diberi UH 4 jam dan dapatkan UH -12 jam dengan menggubakan kaeadah tindihan

REFERENCES • http: //www. ce. utexas. edu/prof/mckinney/c e 374 k/Overheads/12 -Runoff. Processes. pdf