Regionalizalion in Hydrology (Proceedings of the Ljubljana Symposium, April 1990). IAHS Publ. no. 191, 1990.

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1 Regionalizalion in Hydrology (Proceedings of the Ljubljana Symposium, April 199). IAHS Publ. no. 191, 199. Regionalization of parameters using basin geology, land use, and soil type for use in a storm rainfall-runoff relationship YOSIHISA ANDO Department of Civil Engineering, Faculty of Technology, Tokyo Metropolitan University, Fukasawa 2-1-1, Setagaya-ku, Tokyo 158, Japan Abstract The author tries to regionalize parameters using basin geology, land use, and soil type for use in a storm rainfall-runoff relationship. The study covers 31 mountainous basins in Japan. The storm rainfall-runoff relationship is expressed as follows: '-G * P «P <p 1 *P^f l *{P-p 1 ) p^p where D = direct runoff (mm), P = storm rainfall (mm), / = base runoff rate, p x = the first critical rainfall depth (mm), /j = the first additional runoff rate. It is shown that / is equivalent to the ratio of saturated area to the catchment area, and that p x is about mm, varying with basin geology. /(= f + / 1 ) is analysed statistically with basin geology and soil type. Multiple regression analysis of / is done in which / is the dependent variable and ratios of different soil covers to the catchment area are independent variables for each basin geology. Régionalisation de paramètres à partir des caractéristiques géologiques du bassin, de l'utilisation, des types de sol en vue de l'emploi dans les relations précipitations-écoulement averse par averse Résumé L'auteur essaye de régionaliser les paramètres à partir des données géologiques du bassin, du mode d'utilisation des sols, du type de sol pour utilisation dans une relation précipitationécoulement averse par averse. L'étude concerne 31 bassins de montagne au Japon. La relation précipitation-écoulement s'exprime comme suit: D_ ff *P SP< Pl \f *P+f 1 *(P-P 1 ) P X $P où D = lame d'écoulement direct en mm, P = hauteur de précipitation de l'averse en mm, / Q = taux d'écoulement de base, p x = la première hauteur critique de précipitation en mm, / x = la valeur du premier écoulement additionnel en mm. On montre que / est équivalent au rapport entre la surface de la zone saturée et la surface du bassin et que p t est de mm environs, il varie avec la nature géologique du bassin. La fonction / (= / + /,) est 211

2 YosihisaAndo 212 INTRODUCTION analysée par voie statistique à partir des conditions géologiques des bassins et des types de sols. On procède à une analyse de régressions multiples de / dans lesquelles / est la variable dépendante et les rapports des surfaces des différentes couvertures de sols à la surface du bassin sont les variables indépendantes pour chaque types de conditions géologiques des bassins. The storm rainfall-runoff relationship is important to estimate effective rainfall for runoff analysis. Many factors are thought to affect the storm rainfall-runoff relationship of mountainous basins, such as basin geology, land use, soil type, soil moisture condition. In this paper, regionalization of parameters using basin geology, land use, and soil type is done for use in a storm rainfall-runoff relationship. STORM RAINFALL-RUNOFF RELATIONSHIP If the data of rainfall and discharge are given, direct runoff of a net storm rainfall can be obtained by a simple hydrograph separation method. Ando & Takahasi (1981) showed the relationship between a net storm rainfall (P) and direct runoff (D) was (see Fig. 1): IV P «P <p l D * P + f (1) (P - P r X ) PliP o * h When the rainfall depth P is less than p x, it is considered that rainfall onto the saturated areas (channels, swamps and lakes) becomes direct runoff and that rainfall onto the infiltration area (hilltops and hillsides) infiltrates into the soil. Here, f Q was termed as "the base runoff rate". On the other hand, in the case of rainfall whose depth P is more than p v D is expressed as in the second equation in equation (1). If P exceeds p v runoff phenomena alter. 1 - fo-p < P < p 1 f -P + fj(p - Pj) P! < P 5 Fig. 1 5 Pi 1 15 P (nm) Storm rainfall-runoff relationship. 2

3 213 Regionaltation of parameters for a rainfall-runoff relationship As a result, p 1 was named "the first critical rainfall depth". Namely, when P exceeds p v f 1 *(P- pj joins f Q * P as direct runoff. The physical meaning of / x * (P - p 1 ) is both overland flow and interflow, "/j" was named "the first additional runoff rate". Then equation (1) is thought to represent "partial source area concept" introduced by Kirkby (1978). The relationship between P and D is expressed by the lines which are depicted in Fig. 1. STUDY BASINS The study basins are the 31 dam basins shown in Fig. 2. They are located throughout Japan, and are mountainous basins with uniform geology. Basin geology is classified into five categories: Quaternary rocks, Tertiary volcanic rocks, granitic rocks, Mesozoic formations, and Palaeozoic formations. These basins have no artificial water intake or control. They have catchment areas from 22 to 85 km 2. Fig. 2 Locations of the study basins.

4 Yosihisa Ando 214 REGIONALIZATION OF PARAMETERS USING BASIN GEOLOGY, LAND USE AND SOIL TYPE The parameters of the storm rainfall-runoff relationship for the 31 study basins are shown in Table 1. Table 1 Parameters of the storm rainfall-runoff relationship No Name of basin Area ( km 2 ) Quaternary volcanic rocks 1 Serikawa dam Tsuruta dam 85 3 Shimouke dam 185 Tertiary volcanic rocks 4 Kamafusa dam Uchikawa dam 6 Wagatani dam 86 7 llanayama dam Saikawa dam 58 9 Yuda dam Subari dam 1 Granitic rocks Hinamihata dam Shintoyone dam Yahagi dam Kimigano dam Tamagawa dam Fube dam Kijiyama dam Hesozoic formations 18 Ayaminami dam 19 Watarikawa dam 2 Ayakita dam 21 Tachibana dam 22 Hiwa dam Paleozoic formations 23 Shimokubo dam 24 Yokoyama dam Rikimaru dam 26 Ohno dam 27 Kamiichikawa dam 28 Kagami dam 29 llinokawa dam 3 Kanogawa dam 31 Sasaugawa dam f» f, f i f, Pi (mm) The mean value of p x is 54 mm, and values of p 1 vary from 4 to 7 mm. Values of p l for basins covered with Quaternary volcanic rocks and granitic rocks are rather large, and those for basins covered with Palaeozoic formations are relatively small. The mean value of f Q is.1, and values of/ vary from.4 to.17. Figure 3 shows saturated areas such as streams, lakes and paddy fields in five basins. Figure 4 shows the relationship between f Q and a Q (ratios of the

5 215 Regionalization of parameters for a rainfall-runoff relationship saturated area to the catchment area), which indicates that f Q is almost equivalent to a Q. Thus, land use affects /. Then, parameter / (= / + /j) is analysed with a multiple regression analysis for basins with (a) volcanic rocks, (b) granitic rocks, (c) Mesozoic formations and (d) Palaeozoic formations. "/' is taken as a dependent variable yy> 5.uchiyama dam.rikirnaru dam <l^> Paddy field Fig. 3 Saturated areas in five basins n? U Fig. 4 Relationship between f Q and a Q

6 Yosihisa Ando 216 and ratios of different soil covers to the catchment area are taken as independent variables. The linear multiple regression equations are as follows: / = b x * x x + b 2 * x 2 + b 3 * * 3 + b 4 * x 4 (2) where x x = ratio of the area covered by group 1 soil type (which has a big infiltration capacity) to the catchment area, x 2 = ratio of the area covered by group 2 soil type (which has a medium infiltration capacity) to the catchment area, x 3 = ratio of the area covered by group 3 soil type (which has a small infiltration capacity) to the catchment area, x A = ratio of the area covered by group 4 soil type (which has a very small infiltration capacity) to the catchment area, b v b 2, b-, and b. are regression coefficients. Table 2 Values of f and percentage of basin area covered by the four soil types for each basin Soil type Group 1 Group 2 Group 3 Group 4 Infiltration capacity big medium small very small No Name of basin f Per cent of covered area (%) Quaternary volcanic ro cks 1 Serikawa dam Tsuruta dam Shimouke dam Tertiary volcanic rock s 4 Kamafusa dam 5 Uchikawa dam 6 Wagatani dam 7 Hanayama dam 8 Saikawa dam 9 Yuda dam 1 Subari dam Granitic rocks 11 Minamihata dam 12 Shintoyone dam 13 Yahagi dam 14 Kimigano dam 15 Tamagawa dam 16 Fube dam 17 Kijiyama dam Mesozoic formations Ayaminami dam Watarikawa dam Ayakita dam Tachibana dam Hiwa dam Paleozoic formations Shimokubo dam Yokoyama dam Rikimaru dam Ohno dam Kamiichikawa dam Kagami dam Hinokawa dam Kanogawa dam Sasaugawa dam

7 217 Regionalization of parameters for a rainfall-runoff relationship Table 3 Results of multiple regression analysis Basin geology Multiple correlation coefficient Quaternary or Tertiary volcanic rocks Granitic rocks Mesozoic or Palaeozoic formations _ in 8 ^.5 O Volcanic rocks Q Grani lie rocfcs * Mesozoic or Pal eozoic formations io m /So * A / O / / o. a /J A Fig. 5 Correlation o// cal and f obs. Values of / and percentage of area covered by the four soil types for each basin are shown in Table 2. Results of multiple regression analysis for three basin geologies are listed in Table 3. According to Table 3, multiple correlation coefficients are rather high, more than.8; and values of b v b 2, b 3 have a tendency to be b 1 < b 2 < by These results are physically suitable. Correlation of / ca[ (calculated f) and / obs (observed f) are depicted in Fig. 5, which shows agreement between both values. CONCLUSION The main results obtained in this study are: (a) It is indicated that parameter f Q equals the ratio of the saturated area to the catchment area. (b) Multiple regression analysis on "/' shows that parameter / (= / + / x ) can be estimated from the areas of four soil types for each basin geology. Thus the author succeeds in regionalization of parameters by basin geology, land use, and soil type for use in a storm rainfall-runoff relationship.

8 Yosihisa Ando 218 Acknowledgements The author wishes to express his thanks to Professor Yutaka Takahasi (Shibaura Institute of Technology), Mr Norio Yoshida (former student of Tokyo Metropolitan University) and Mr Takashi Nabeyama (Research Associate of Tokyo Metropolitan University) for their assistance. REFERENCES Ando, Y. & Takahasi, Y. (1981) A hydrological model of hillslope basins. /. Faculty of Engineering, Univ. Tokyo (B) 36 (2), 27-. Kirkby, M. J. (1978) Hillslope Hydrology. John Wiley & Sons.