Nnth Internatonal Water Technology Conference, IWTC9 2005, Sharm El-Shekh, Egypt 37 HYDROGRAPH ESTIMATION IN SEMIARID REGIONS USING GIS SUPPORTED GIUH MODEL Hafez Shaheen, Anan Jayyous, Sameer Shadeed 2 and Ammar Jarrar 2 Cvl Engneerng Department, An-Najah N. Unversty, Nablus, Palestne 2 Water and Envronmental Studes Insttute, An-Najah N. Unversty, Nablus, Palestne ABSTRACT Among the most basc challenges of hydrology are the quanttatve understandng of the processes of runoff generaton and predcton of the flow hydrographs and ther transmsson to the outlet. Tradtonal technques have been wdely appled for the estmaton of runoff hydrographs at the outlets of gauged watersheds usng hstorcal ranfall-runoff data and unt hydrographs derved from them. Such procedures are questoned for ther relablty due to the clmatc and physcal changes n the watershed and ther applcaton to ungauged, ard and semard catchments. To overcome such dffcultes, the use of physcally based ranfall-runoff estmaton methods such as the Geomorphologc Instantaneous Unt Hydrograph (GIUH) approach has evolved. In ths study, the lately developed GIUH model s appled to Al-Badan watershed of Fara catchment located n the northeastern part of the West Bank, Palestne. The Fara catchment characterzes a semard regon, wth annual ranfall depths rangng on average from about 50 to 600 mm. The Geographcal Informaton System (GIS) technques are used to shape the geomorphologcal features of the catchment. The applcaton of the GIS supported GIUH model has proved reasonable agreement between the smulated runoff hydrograph and the recorded flows. The paper has elaborated on the applcablty of the unt hydrograph theory and the GIUH to semard regons. Keywords: GIUH; GIS; Flow hydrographs; Semard regons. INTRODUCTION The computaton of flow hydrograph characterstcs s a major concern of water resources engneers and scentsts. The nature of stream flow n a catchment s related to the ranfall characterstcs and watershed geomorphology. The ranfall characterstcs are the temporal and spatal dstrbuton of the ranfall quantty. The geomorphc characterstcs are the channel network, topography, and surroundng landscape, whch translate the ranfall nput nto an output hydrograph at the outlet of the watershed. Tradtonally the
372 Nnth Internatonal Water Technology Conference, IWTC9 2005, Sharm El-Shekh, Egypt unt hydrograph approach s beng appled for ranfall-runoff modelng for all knds of catchments ncludng ard and semard regons. Shaheen [] has nvestgated the ranfallrunoff process n semard regons. He has concluded that such watersheds actng as partal contrbutng and varable resources do not obey the assumptons of the tradtonal unt hydrograph approach. Runoff n such watersheds s subsurface flow domnated nstead of surface flow domnated and the nteracton between surface and subsurface flows can not be neglected as the case n the tradtonal unt hydrograph theory. A sgnfcant advance n the unt hydrograph approach for ungauged watersheds s the development of the Geomorphologc Instantaneous Unt Hydrograph (GIUH) (Yen and Lee [2] and Lee and Yen [3]). In the GIUH approach, ranfall excess s assumed to follow dfferent paths on overland areas and n channels of dfferent stream orders to reach the watershed outlet. Geomorphology based nstantaneous unt hydrographs have been appled by several engneers to produce runoff from ranfall for ungauged watersheds. They have been proposed to estmate floods for ungauged streams by usng only the nformaton obtanable from topographc maps or remote sensng possbly lnked wth the Geographc Informaton Systems (GIS) and Dgtal Elevaton Model (DEM) (Snell and Svapalan [4], Jan et al. [5], and Hall et al. [6]). The objectve of ths study s to apply the GIS supported GIUH approach for the estmaton of flow hydrographs n semard regons. Wth the gven geomorphc propertes of the watershed, the unt hydrograph can be determned hydraulcally wthout usng any recorded data of past ranfall or runoff events. Ths approach reduces the excessve topographc data and computatonal efforts requred n full hydrodynamc determnstc routng of watershed runoff. The nteracton between the surface and subsurface flows can be consdered n such an approach through the varaton of the nfltraton parameters and thus attanng the ranfall-runoff process n ard and semard regons. GIS provde a dgtal representaton of the watershed characterzaton used n hydrologc modelng. GIS can also provde the bass for hydrologc modelng of ungauged catchments and for studyng the hydrologc mpact of physcal changes wthn a catchment. The ntegraton of GIS nto hydrologc models follows one of the two approaches: () develop hydrologc models that operate wthn a GIS framework, () develop GIS technques that partally parameterze exstng hydrologc models. Jan et al. [5] has appled the second approach to Gambhr rver catchment n Inda and concluded that the peak characterstcs of the flows are more senstve to the varous storm pattern as well as method of crtcal sequencng followed for the computaton of the desgn storm. The avalable GIUH program (verson.2) can be appled to watersheds wth stream network of up to the seventh order. It has been developed by Kwan Tun Lee and Chn- Hsn Chang, Watershed Hydrology and Hydraulcs Laboratory, Department of Rver and Harbor Engneerng and Natonal Tawan Ocean Unversty. GIUH can be appled to any
Nnth Internatonal Water Technology Conference, IWTC9 2005, Sharm El-Shekh, Egypt 373 excess ranfall through convoluton to produce the drect runoff hydrograph. The approach s appled here to Al-Badan watershed of the upper Fara catchment of the West Bank, Palestne. The results are compared to the tradtonal SCS approach to further verfy the applcablty of the GIUH model to semard regons. The relatve matchng between the smulated runoff hydrograph and the recorded flows seems reasonable and wthn the acceptable lmts. STUDY AREA The area under consderaton s the Fara catchment located n the northeastern part of the West Bank. It les wthn the Eastern Aqufer Basn (EAB) and has a catchment area of about 330 km 2. EAB s one of the three major groundwater basns underlyng the West Bank area and formng the West Bank water resources. The Fara catchment extends from the rdges of Nablus Mountans down the eastern slopes to the Jordan Rver. The upper porton of the Fara catchment extends 25 km east of Nablus cty to Al-Malaq Brdge, where the two man streams contrbutng to the Fara catchment meet. These are Al-Fara and Al-Badan streams. The upper Fara catchment s about 7 km 2 representng 35% of the total Fara basn. The two man sub-catchments formng upper Fara basn are Al-Fara of about 63.8 km 2 and Al-Badan of about 53.4 km 2. The annual average ranfall ranges from 600 mm at the headwater to 50 mm at the outlet to the Jordan Rver. The GIUH approach s appled here to Al-Badan watershed. Fgure shows Al-Badan watershed and the ranfall dstrbuton wthn the Fara catchment. In Fara catchment, daly ranfalls are avalable for 6 statons but for dfferent number of years and not as contnuous tme seres except for Nablus staton. Ranfall ntensty readngs are also avalable for two statons n the Fara basn, Nablus and Bet Dajan, and for about three to nne years only. Nablus and Talluza statons have the largest average annual ranfall and Fara staton has the lowest. It s noted also that Tubas staton has average annual ranfall of about 45 mm, whch nearly equals the average of the annual average ranfalls of the sx statons wthn the Fara catchment at about 430 mm. In general, ranfall averages decrease movng from north to south and west to east. No enough runoff data are recorded for the Wad Fara dranage basn. Most of the data avalable are monthly data estmated usng drect measurements of the runoff at selected locatons and perods of the year. Therefore and to collect ranfall-runoff data necessary for the detaled modelng of storm events, the Water and Envronmental Studes Insttute (WESI) constructed, August 2002, two Parshall flumes at Al-Malaq Brdge. The flumes are to measure the flows at the two man streams of upper Fara catchments, Al-Fara and Al-Badan. The flumes were constructed n context of GLOWA project (Impacts of global
374 Nnth Internatonal Water Technology Conference, IWTC9 2005, Sharm El-Shekh, Egypt changes on surface water resources n wads contrbutng to the lower Jordan Rver basn). Maxmum and mnmum flows that can be measured by the flumes at Al-Fara and Al-Badan are 5 m 3 /s, 0.9 m 3 /s and 25 m 3 /s, 0.23 m 3 /s respectvely. N 600 350 450 400 600 350 300 250 20 0 200 50 Jordan Rver Streams Annual Average Ranfall (mm) Watershed Boundary Badan Watershed 0 3 6 9 2 Klometers Fgure : Al-Badan watershed and ranfall dstrbuton wthn the Fara catchment The eastern slopes of the West Bank area, where Fara catchment s located, are characterzed as semard. Ard regons are those n whch ranfall on a gven pece of land s not suffcent for regular crop producton whereas semard areas are those n whch the ranfall s suffcent for short season crops and where grass s an mportant element of the natural vegetaton. The hydrologcal characterstcs of surface runoff vary wth land use and seasons. In ard and semard regons, the degree of slope exercses a strong control on the amount of runoff than n humd areas. On the hllsde, the ntal losses beng compensated by steeper gradents, bare rocky surfaces and low wastage through vegetaton, but ran fallng on gently slopng plans wll be less effectve n producng runoff than n humd areas (Chow [7]). These geomorphc characterstcs are reflected n the parameters estmaton requred for the applcaton of the GIUH model. GIS tools are to facltate these estmatons.
Nnth Internatonal Water Technology Conference, IWTC9 2005, Sharm El-Shekh, Egypt 375 METHODOLOGY AND RESULTS The boundary of Al-Badan watershed and all ts flow paths and streams have been mapped usng the avalable GIS program. The maps n ther dgtal forms have been used to estmate the nput parameters of the GIUH. Strahler's stream orderng system has been followed. Accordng to ths system, t was found that Al-Badan watershed s of the fourth order. For Al-Badan watershed, the elevaton vares from 680 to 90 m above sea level. Fgure 2 shows the dranage network map and the stream orders of Al-Badan watershed. Fgure 2: Dranage network and the stream orders of Al-Badan watershed The procedure for the applcaton of the GIUH model suggested by Lee and Yen [3] s appled here to produce the IUH for Al-Badan watershed. The values of the overland and channel roughness coeffcents, n o and n c, are respectvely kept constant for the watershed. The nput ranfall s taken as cm and the ranfall duraton as one hour. The mean of the dranage area of order and the rato of th-order overland area to the watershed area are estmated usng the two equatons respectvely: A P OA = N N j= A j = N A A = N A P xxj (2) ()
376 Nnth Internatonal Water Technology Conference, IWTC9 2005, Sharm El-Shekh, Egypt It should be noted that A j denotes not only the areas of the overland flow regons that drans drectly nto the jth channel of order, but t also ncludes overland areas dranng nto the lower order channels trbutary to ths jth channel of order. The stream network transtonal probablty of the randrop movng from an th-order channel to a jth-order channel s computed as: P xxj = N, j N (3) The other parameters needed for the applcaton of the GIUH program have been estmated and are lsted n Table. The resultng IUH hydrograph for Al-Badan watershed due the applcaton of the GIS supported GIUH model followng the above procedure s shown n Fgure 3. Table : GIUH nput parameters for Al-Badan watershed Stream Order Parameter 2 3 4 N 32 5 2 L c (km).32 2.692 4.798 3.65 A (km 2 ) 0.939 5.86 24.775 53.3568 P OA 0.563 0.228 0.37 0.073 S c (m/m) 0.028 0.0388 0.0424 0.0284 S o (m/m) 0.07 0.09 0.0356 0.0284 Area (km 2 ) 53.355 Base flow (m 3 /s) 0.74 n o 0. n c 0.04 B (m) 4.57 Ω P x x j P,2 P,3 P,4 P 2,3 P 2,4 P 3,4 8/32 4/32 0/32 5/5 0/5 2/2
Nnth Internatonal Water Technology Conference, IWTC9 2005, Sharm El-Shekh, Egypt 377 The prmary goal of developng IUH of a watershed s to apply t for hydrograph generaton for desgn or project storms. Durng the rany season of 2003, only one consderable storm was recorded and can be smulated here. The pont ranfall recorded at Nablus meteorologcal staton located near the headwater was averaged over the watershed to consder the varaton n the ranfall dstrbuton wthn the watershed. The ranfall sohyets method was appled for ths purpose. As to the sem-ardty and due to the Karstc nature of the rock formaton of the Palestnan aqufers, a hgh percentage of the ranfall nfltrates. The ranfall-runoff rato n the West Bank has a wde varaton (0.% to 6.3%) ndcatng that a small porton of the ranfall s converted to runoff []. Excess ranfall of the ranfall event was determned. The total ranfall of 4/2/2003 smulated event s about 40 mm measured as pont ranfall at Nablus staton. To estmate the excess ranfall (ER), Horton method was appled. The resultng excess ranfall from the above storm s about 6mm dstrbuted as shown n Fgure 4. Based on the above methodology and usng the GIS and the dgtal maps, the storm s appled to the generated GIUH and the drect runoff hydrograph s estmated. The GIUH estmated hydrograph and the recorded data for the smulated ranfall-runoff event of Al- Badan watershed are shown n Fgure 4. The estmated and recorded flow values match reasonably. The dfference between the estmated and recorded peak flow at tme t = 7 hrs s less than 0%. Also the fgure reflects good match n both the tme to peak and the lag tme. Q (m3/s) 45 40 35 30 25 20 5 0 5 0 0 2 4 6 8 0 2 4 6 8 20 Tme (hr) Effectve Ran = cm Fgure 3: Generated GIUH flow hydrograph for Al-Badan watershed
378 Nnth Internatonal Water Technology Conference, IWTC9 2005, Sharm El-Shekh, Egypt In ths context, t s to note here that the assumpton of unformly dstrbuton of the excess ranfall over the watershed s not consstent wth the sem-ardty nature of the Palestnan watersheds that behave as varable sources and partally contrbutng. Nevertheless, the results of the smulaton of the event usng the GIS supported GIUH are promsng and ndcate the applcablty of the model to semard regons. Tme (hr) 40 0 5 0 5 20 25 30 35 40 45 50 55 60 0 Q (m3/s) 35 30 25 20 5 0 5 0 Excess Ranfall Estmated Recorded 2 3 4 5 6 7 8 9 0 ER (mm) Fgure 4: Recorded and estmated drect runoff hydrograph for Al-Badan watershed CONCLUSIONS The hydrologc response of a watershed to excess ranfall nput s lnked to the geomorphc structure of the watershed. Therefore the recently developed GIUH model has been appled by several authors to derve unt hydrographs for several ungauged watersheds. The GIS supported GIUH model s appled here to Al-Badan watershed of the Fara catchment located n the northeastern part of the West Bank, Palestne. The non-avalablty of suffcent ranfall-runoff records has lmted the testng of the valdty of the methodology mplemented here to semard nature watersheds. Nevertheless, the smulaton of the one event recorded durng the wnter of the year 2003 and applyng the GIUH, whch uses the Knematcs Wave Equaton and consders the
Nnth Internatonal Water Technology Conference, IWTC9 2005, Sharm El-Shekh, Egypt 379 detals of the geomorphc characterstcs of the watershed, has resulted reasonable match between the estmated runoff hydrograph and the measured stream flows. Among the mportant lmtatons of the above methodology for applyng the GIS supported GIUH model s the velocty and roughness estmaton of the dfferent order channels. The smulaton of the nteracton between the subsurface and surface flows s needed for the smulaton of the semard regons and Karstc nature watersheds. The partal contrbuton of the semard watersheds to outflow hydrographs s overcome usng dfferent nfltraton parameters for each of the dfferent order channels. Abbrevatons: N number of th-order channels. L c mean th-order stream length A th-order sub watershed contrbutng area POA rato of th-order overland area to the watershed area S c mean th-order channel slope S o mean th-order overland slope n o overland flow roughness n c channel flow roughness B Ω channel wdth at watershed outlet P stream network transtonal probablty x x j N, number of the th-order channels contrbutng to jth-order channels j REFERENCES. Shaheen H.Q., Storm water dranage n ard and semard regons: West Bank as a case study, An-Najah Unversty Journal for Research - A (Natural Scences), Vol. 6, No. 2, pp. 25-39, Nablus, 2002. 2. Yen, B.C., and Lee, K.T., Unt hydrograph dervaton for ungauged watersheds by stream-order laws, Journal of Hydrologc Engneerng, ASCE, Vol. 2, No., pp. -9, 997. 3. Lee, K.T., and Yen, B.C., Geomorphology and knematc-wave-based hydrograph dervaton, Journal of Hydraulc Engneerng, ASCE, Vol. 23, No., pp. 73-80, 997.
380 Nnth Internatonal Water Technology Conference, IWTC9 2005, Sharm El-Shekh, Egypt 4. Snell, J.D., and Svapalan, M., On geomorphologcal dsperson n natural catchments and the geomorphologcal unt hydrograph, Water Resources Research, Vol. 30, No. 7, pp. 23-2323, 994. 5. Jan, S.K., Sngh, R.D., and Seth, S.M., Desgn flood estmaton usng GIS supported GIUH approach, Water Resources Management, Vol. 4, pp. 369-376, 2000. 6. Hall, M.J., Zak, A.F., and Shahn, M.A., Regonal analyss usng geomorphoclmatc nstantaneous unt hydrograph, Hydrology and Earth System Scences, Vol. 5, pp. 93-02, 200. 7. Chow, V.T. (Ed.), Handbook of Appled Hydrology, A Compendum of Water Resources Technology, McGraw Hll book Company, New York, 964.