こうえいフォーラム第９号／２００１．１

AN ENGINEERING APPROACH TOWARDS APPROPRIATEHYDROLOGICAL WATER CYCLE IN URBAN AREAS : FIRSTREPORT
都市域における望ましい水循環系構築に向けての工学的アプローチ

忌部正博*・中野裕**・中嶋則行***・中村茂****・小川田大吉***
Masahiro IMBE, Yutaka NAKANO, Noriyuki NAKASHIMA, Sigeru NAKAMURA and Daikichi OGAWADA

本論文は、都市化により悪化した水循環を改善する水循環再生構想策定における技術的アプローチを示したものである。具体的な検討を行うにあたり、新河岸川流域（流域面積390km2）を取り上げ、過去、現在、将来の水循環の定量評価を数値計算モデルにより行った。
水循環再生のための目標値の設定は、行政と流域住民の合意形成を経て、注意深く行う。水循環改善に関わる対策は、様々な組み合わせがあり、得失を定量的に踏まえた上で決定していく。また、流域内関係者の合意形成を行いやすくするための策定組織を提案した。さらに、技術的な評価を流域内関係者に理解しやすい形で示していくことの重要性も示した。

Key Words : hydrological water cycle, water environment, engineering assessment,
consensus building, comprehensive master plan

１．INTRODUCTION

Ministry of Construction in Japan set up a committee to draw up

Urbanization generally boosts expansion of urban areas,a manual for planning the renewal of hydrological water cycle in

improvement of lifestyles, high population density and highurban areas. The paper [2] explains the design concept

grade of land utilization. Those urbanization processes haveauthorized by the committee which was finally involved into theresulted in an expansion of impermeable areas such as roofs andmanual [3]. According to the paper [2], the word ofpavements, an increase in water demand, an increase in"hydrological water cycle" is useful for the discussion amongindustrial and domestic waste water and a reduction of water

the people with different backgrounds to plan the comprehensive

surface areas and green lands. The phenomena tend to distort themeasures to improve the aqua-environment. The paper [2] also

appropriate hydrological water cycle and bring about theproposes an investigation procedure as shown in Fig.1.

following six issues to be solved [1] : 1) Increase of ordinary

Recently, an interim report "How should an appropriate waterwater discharge, 2) Flood control, 3) Conservation andcycle be in river basins." [4], proposed in July,1998 by the sub-development of water resources, 4) Conservation and revival ofcommittee of water cycle, the River Council for river control,

ecological System, 5) Pollution control and 6) Improvement ofproposed the necessity of a sustainable water cycle. This reportheat environment.

[4] also pointed out that comprehensive master plans for

In order to implement a policy for solving these issues, theappropriate water cycle should be urgently drafted for urbanizedareas which suffer from serious problems concerning thedeterioration of water cycle.

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社団法人 雨水貯留浸透技術協会
大阪支店 技術第一部
首都圏事業部 河川・水工部
中央研究所 開発研究部

This paper presents only the preliminary consideration applied
for the study area in order to draft a comprehensive master plan
for an appropriate water cycle. This study is supposed to95

An Engineering Approach towards Appropriate Hydrological Water Cycle in Urban Areas : First Report

Fig.1 Investigation procedure for planning the renewal of hydrological water cycle

Table 1. Basic urbanization data for the Shingasi River Basin (as of 1990)

continue in order to finalize the comprehensive master plan.

The lowland areas are covered with silty soil. The terrace
areas are covered with a layer of the Kanto loam which is 2 to２．OUTLINE OF STUDY AREA

10 meters thick with a gravel layer approximately 30 meters

The Shingasi River of the study area is a tributary of thethick underneath. Groundwater levels are generally low, about 5

Arakawa River and runs northeast of Tokyo. Most of theto 10 meters below the surface. The direction of the groundwater

catchment area belongs to Saitama prefecture and has beenaligns with the configuration of the land. Saturated hydraulicrapidly urbanized since the 1950s when the Tokyo metropolitan

conductivities are approximately 1 x 10-3 to 5 x 10-2 cm/s in thearea was widened to involve this area. The Shingasi River has

Kanto loam, 1 x 10-4 cm/s in the silt and 1 x 10-2 cm/s in thefive major tributaries namely Shirako River, Kurome River,gravel. Fig.2 shows the distribution of the contour line of theYanase River, Sunagawabori River, and Furo River. The basic

unconfined ground-water and the saturated hydraulicurbanization data are tabulated in Table 1.

conductivities of the surface soil.

The Shingasi River Basin comprises two different areas,lowland and terrace. The lowland is of an alluvium spread along

３．EXTRACTION OF PROBLEMS AND ISSUES

the main stream. The terrace occupies a large area along theChanges of water cycle in the Shingasi River Basin, from thetributaries. The gradient of the basin is 1/1000 to 1/4000 in thepast to the present as well as changes predicted in the future,main stream areas, and 1/100 to 1/400 in the tributary areas.

have been estimated by focusing on the influential factors. The
quantitative estimation was conducted by applying the96こうえいフォーラム第９号／２００１．１

Fig.2. Contour lines of the unconfined groundwater and saturated hydraulic conductivities of the surface soil

simulation model which represents the physical characteristics

the decrease of base runoff. In addition to the absence of waterof the natural flow mechanism of a river basin [5]. The pastamenity, the utilzation of water for emergency has becomerefers to around the year 1945 when the basin was assumed to bedifficult.

in a natural state. The future is supposed to be the year 2025
when urbanization will have further progressed.

Fig.3(c). shows the change in base runoff of Furo River.
Exponential growth of population from past to present has

Increase of peak flood flow ; Due to the expansion ofincreased runoff of wastewater into the river. The amount ofimpermeable areas and the improvement of urban storm

wastewater is accounted a fair percentage of river water indrainage systems, the present peak flood flow is estimated to bepresent condition. Bypassing wastewater by the sewerage

1.5 times that in 1945 and it is predicted to increase in the futuresystem will decrease base runoff in the future.

as shown in Fig.3(a).

Decline of groundwater level and dry-up of spring water ;Increase of water demand ; Water transmitted from outside ofExcess pumping of groundwater lowers the groundwater level

the basin is significant due to the industrial and living uses. Inand causes ground subsidence. In addition to the excess

the future, all the water supply is predicted to rely on thepumping, the decrease of rainwater infiltration dries up springtransmitted water from outside of the basin and it is equivalentwater and reduces groundwater flow into the rivers. Fig3.(d)to the water volume of the precipitation inside this area as shown

shows the change in groundwater level and Fig3.(e) shows thein Fig.3(b).

change in spring water discharge.

Deterioration of water quality ; Due to the discharge of waste

Change of climate ; The decrease of green land and waterwater, the water quality of the river has been deteriorated assurface (marsh, river etc.) and the increase of exhaust heat cause

shown in Table.2. The river water used to be utilized for thethe change in heat environment. Fig3.(f) shows the change in

agricultural and living use but not now. In proportion to theevaporation quantity.

deterioration of water quality, the area for habitat of animals andplants is decreased and the river has already lost the function as
the water amenity for the local residents.

４．BASIC IDEA FOR SETTING UP PROJECT
GOALSDecrease of base runoff ; The decrease of rainwater

Before setting up the various measures for improving theinfiltration and the bypass of the sewerage system have caused

water cycle, appropriate project goals should be set based on the97

An Engineering Approach towards Appropriate Hydrological Water Cycle in Urban Areas : First Report

Fig.3. Transition of hydrological quantity and quality from past to future

Table 2. Water quality (Biochemical Oxygen Demand : BOD) of dominant rivers in Shingasi River Basin

extracted problems and issues. The viewpoints for the desirablevalues.

image of the catchment area can be classified into two types.

５．SETTING UP MEASURES

One is the effect directly derived by the improvement of water

The available measures and their quantitative effects are listed

cycle and the other is the effect indirectly derived. In otherin Table 3. The quantitative indexes are classified into either

words, one is the quantitative index for the amount of water orthe effect directly specified or the effective factor related

the water quality such as water discharge, ground-water level,indirectly with the specified effect. For example, the influential

biochemical oxygen demand (BOD) etc., which is rather anfactor of a quantity of infiltration is related with various effects

engineering approach. The other is the environmental condition

such as flood discharge, ordinary river discharge andrelated with aqua-culture, ecological system, water amenity etc.,

groundwater level. It means that the infiltration facility is

which is more understandable for ordinary inhabitants in spite ofeffective for not only flood control but also aqua-environment.

the difficulty for the quantitative estimation. It is very important

The various measures listed in Table 3 should be allotted among

to explain the relationship between the improvement of water

the government, inhabitants, and private enterprises depending

cycle and the life of inhabitants and to present project goals thaton their characteristics.

we understandable for not only engineers but also ordinary
inhabitants.
It is necessary to consider various viewpoints such as the past

６．CO-OPERATIVE SYSTEM FOR DRAFTING
MASTER PLAN

condition, the intention of inhabitants, the political goals and theIn order to build the consensus of the master plan among theability of implementation, etc., to set up the appropriate target

government, the inhabitants, and the enterprises, as co-operative98こうえいフォーラム第９号／２００１．１

Table 3. Relation between available measures and quantitative effects99

An Engineering Approach towards Appropriate Hydrological Water Cycle in Urban Areas : First Reportsystem should be carefully constructed. Under this organizing

discussed from the various view points not only with thesystem, the master plan should be authorized by the river council

governments but also with the local residents.

which consists of the representatives from the Ministry ofIt is also important to select the most suitable plan among theConstruction, the local governments, and the tributary working

various alternatives. The effectiveness of each alternative can begroups.

calculated, but in order to make the master plan comprehensible,

Before the river council finalizes the master plan, the eachreasonable and sympathetic, the great effort should be paid fortributary working group should build the consensus through theproducing the positive activity of the organizing system anddiscussion among the academic advisories of professors, theinterpreting the engineering assessment to be easily

administrative officers of relevant local governments, and someunderstandable for all the relevant members.

local residents. During this process, it is also very important toencourage the relevant members through social gathering,
explanation and discussion, symposium, festival and so on.

７．CONCLUSIONSThis paper indicates the investigative procedure andconsideration to draw up the master plan for the appropriatehydrological water cycle. The problems and issues of the water
cycle in the Shingasi River Basin were extracted and explainedin this first report.
According to the future schedule, many steps of discussion
should be done under the organizing system presented in thispaper in order to build the consensus among the governments,
the inhabit-ants and the enterprises. To make the results
successful, the desirable image of water cycle should be100

REFERENCES
１）Imbe M., Ohta T., Takano N. (1995) Methodological approach to improve
the hydrological water cycle in urbanized areas, Proceedings on theSecond International Conference on Innovative Technologies in Urban
Storm Drainage, Lyon, France, pp.37-44２）Musiake K., Kubota M., Imbe M., Takano N., Dan T. (1999) Designconcept for renewal of hydrological water cycle in urban area, Proceedingson the 8th International Conference on Urban Storm Drainage, Sydney,Australia, Vol.1, pp.232-239
３）The Ministry of Construction in Japan (1998) The Manual for Planning theRenewal of Hydrological Water Cycle in Urban Areas (in Japanese)４）The Sub-committee of Water Cycle under the River Council for River
Control (1998) How should an appropriate water cycle be in river basins,
The Interim Report (in Japanese)５）Nakamura S, Saito M, Herath S. (1996) Development and applications ofa physically based distributed catchment model in urban area, International
Conference on Urban Engineering in Asian Cities in the 21st Century,
proc. vol. II, pp. F. 128-223