4~JD IRECTORATE GENERAL OF WATER RESOURCES DEVELOPMEIJT MINISTRY OF PUBLIC WORKS REPUBLIC OF

TUNTANG/JRAGUNG RIVERS BASINS

INTEGRATED DEVELOPMENT PLAN

SPECIAL REPORT III

FLOOD CONTROL AND DRAINAGE

NOVEMBER 1979

SUBMITTED BY

PRC ENGINEERING CONSULTANTS, INC. ENGLEWOOD, COLORADO, U.S.A. , INDONESIA DIRECTORATE GENERAL OF WATER RESOURCES DEVELOPMENT MINISTRY OF PUBLIC WORKS REPUBLIC OF INDONESIA

TUNTANG/JRAGUNG RIVERS BASINS

INTEGRATED DEVELOPMENT PLAN

SPECIAL REPORT III

FLOOD CONTROL AND DRAINAGE

NOVEMBER 1979

SUBMITTED BY

PRC ENGINEERING CONSULTANTS, INC. ENGLEWOOD, COLORADO, U.S.A. SEMARANG, INDONESIA PREFACE

The Directorate General of Water Resources Development (DGWRD) of the Ministry of Public Works, Government of Indonesia (GOI) contracted PRC Engineering Consultants, Inc. (PRC/ECI) to provide consulting engineering service for preparing an integrated development plan for the Tuntang/Jragung Rivers in the Jratunseluna Basin. The study for the preparation of the plan starLed on May 16, 1979 and was scheduled to be completed on November 30, 1979.

An interim report on the study was submitted by PRC/ECI on August 15, 1979 which was reviewed by all the concerned agencies and later discussed on September 24, 1979 in a meeting held by the DGWRD at . In that meeting and in subsequent discussions between PRC/ECI and DGWRD, it was the consensus of opinion of all the participants that it would be very beneficial if the study on the Tuntang/Jragung Rivers could be modified by including the entire Jratunseluna Basin in certain aspects of the study. In that modified study the interrelationships of the existing, proposed and the potential development works of the Tuntang/Jragung subbasins and those of the adjoining subbasins within the Jratunseluna Basin should be examined. Thus, the master plan for the development of the Jratunseluna Basin which was prepared earlier by NEDECO in the year 1973, would be reviewed and updated. The changes in criteria and constraints which have occurred and the large amount of new data which have become available since preparation of the original master plan would be incorporated in the modified study for formulating a conceptual optimized development plan.

For the preparation of the integrated development plan for the 'rLntang/Jragung Rivers, as contemplated originally, reports were pm'epared in all the relatcd Fields for supporting the proposed plan. Those reports were to become appendices to the final report on the in­ tegrated development plan. However, due to the proposed modification of the study to increase its scope in certain aspects tu include the entire Jratunseluna Basin it has become necessary to either rewrite or modify some of the supporting i±eports related to the specific fields of the modified study. Those modified reports will then be appended to the final report for the updated Jratunseluna Basin Development Plan.

There were certain such supporting reports which were written exclusively for the originally proposed integrated development plan for the Tuntang/Jragung subbasins. The subjects covured by those reports will not be studied further in the modified study for updating the Jratunseluia Basin Development Plan. It was, therefore, decided to produce and document those reports as Special Reports. This Special Report III on Flood Control/Drainage is one of the three such reports thus produced.

Semarang, November 1979 PRC Engineering Consultants, Inc. TABLE OF CONTENTS

SPECIAL REPORT III

FLOOD CONTROL AND DRAINAGE

Page

SUMMARY (v)

III.l. GENERAL IIl-1

III III.1.1. Purpose III-1 111.1.2. Scope III-i 111.1.3. General Descriptive Data 111-2 III.1.4. Description of Project Area 111-3 111.1.5 Existing Improvements 111-4 111.1.6. Sedimentation 111-5 111.1.7. Flood Problems 111-6

111.2. BASIS FOR DESIGN 111-8

111.2.1. Surveys 111-8 111.2.2. Soils 111-8 111.2.3. Hydraulic Design 111-9 111.2.4. Alternative Plans Considered III-10 111.2.5. Description of Proposed Plans III-11 111.2.6. Design of Levees 111-15 111.2.7. Design of Channels 111-15 111,2.8. Drop Structures 111-16 111.2.9. Structure Modifications 111-17 111.2.10 Interior Drainage 111-17 111.2.11 Costs Estimates 111-17

111.3. OPERATION AND MAINTENANCE 111-18

(i) TABLE OF CONTENTS (Cont.)

SPECIAL REPORT III

FLOOD CONTROL AND DRAINAGE

Page

111.4. CONCLUSIONS AND RECOMMENDATIONS 111-19

III.4.1. Conclusions 111-19 111.4.2. Recommendations 111-19 III.4.2.q. Hydrology 111-19 III.4.2.b. Field Data 111-19

BIBLIOGRAPHY 111-24

(ii) LIST OF TABLES

SPECIAL REPORT III

FLOOD CONTROL AND DRAINAGE

No. Title Page

III-i Project Design Flows 111-21

111-2 Major Structure Modifications 111-22

111-3 Estimates of Cost 111-23

(iii) LIST OF FIGURES

SPECIAL REPORT III

FLOOD CONTROL AND DRAINAGE

No. Title Unnumbered Tuntang/Jragung Rivers

Location Map

IiI-1 General Map of Study Area

111-2 Sedimentation

111-3 Areas of Inundation

III-it Existing Capacities

111-5 Standard Levee and Channel Sections iII-6 Center-line Profile - Jragung River

111-7 Center-line Profile - Tuntang River

(iv) TUNTANG/JRAGUNG RIVERS BASINS INTEGRATED DEVELOPMENT PLAN

SPECIAL REPORT III

FLOOD CONTROL AND DRAINAGE

SUMMARY

Flooding in the lower reaches of the Jragung and Tuntang Rivers results from ponding from heavy local rainfall and poor drainage and from floodwaters originating from upstream tributaries. The construc­ tion of dams and reservoirs in the upstream reaches of the rivers will only partially alleviate the flood and drainage problems in the Plain of East Semarang. Seven alternative channel improvement plans were in­ vestigated for the purpose of aiding in the selection of the optimum

basin plan. The preliminary alternative plans for flood control and drainage are considered to be engineeringly feasible and will provide a high degree of flood protection to the project area. The principal factors to be considered in the final selection of the optimum basin plan are: engineering and economic feasibility, effect on total overall basin planning and environmental and social cffects.

(v) TUNTANG/JRAGUNG RIVERS BASINS INTEGRATED DEVELOPMENT PLAN

SPECIAL REPORT III

FLOOD CONTROL AND DRAINAGE

III1.. GENERAL

II1.1.1. Purpose

The purpose of this report is to present the results of preliminary field investigations and office studies undertaken to determine the engineering feasibility of providing a plan for flood control and drainage for the lower reaches of the Jragung and Tuntang Rivers. The geographical limits of the study area are shown in Figure III-i. The flood control and drainage study was conducted in conjunction with concurrent studies of the water resources development of the two rivers for multipurpose use. Several potential storage reservoirs are included in the develop­ ment plan. Also, several alternative channel improvement plans were investigated with the primary purpose of providing a high degree of flood protection to the area. A further purpose of this report is to provide a basis for a more detailed study for the future development of a flood control program for the Jragung and Tuntang River systems.

111.1.2. Scope

This report describes various preliminary alternative plans for flood control and drainage on the Jragung and Tuntang River systems based on conditions that would prevail if dams are constructed in the upper rcachet of the two rivers ind on conditions that the dams would not be constructed. Additionally the plaus for channel improvemeiints are based on two levels of protection: 1 in 20 year and 1 in 50 year frequccGes of occurrence. The study was conducted at pre-feasibility

ilI-1 level utilizing data developed by the Proyek Jratunseluna staff and their Consultants, the Netherlands Development Engineering Company (NEDECO). The basis for design and cost estimates for the various alternative plans is presented in sufficient detail to aid in the logical selection of the most feasible plan and to enable the undertaking of more comprehensive and detailed studies of the selected plan in the future if required. Successful development and operation of a selected plan for flood mitigation will have a significant beneficial effect on the rural and agricultural areas within the area of the eastern sector of the Plain of East Semarang.

111.1.3. General Descriptive Data

The Jragung and Tuntang Rivers are located in the eastern sector of the plain of East Semarang wit'in the Jratunseluna Basin of Central (see Figure III-1). The name of the Basin is derived from the contraction of the names of the five principal rivers located within the Basin: Jragung, Tuntang, Serang, Lusi and Juana. All five rivers flow in a north-northeasterly direction into the between Semarang and Rembang. The overall objectives of the on-going water resources development stauies for the Basin are to improve irrigation, municipal water supply, power and flood control and drainage for the purpose of accruing benefits from increased agriculLural production and social well-being.

The Basin comprises a land area of approximately 7,700 km2. Lond surface elevations in the basin range from sea level to the high volcanic peaks of several mountain ranges with a maximum elevation of the Merbabu Volcano of 3,142 m. About 24 percent of the Basin area is comprised of relatively flat alluvial. plains that are extensively cultivated for agricultural production. Myriad natural and artificial waterways segment the coastal plains of the Basin, serving the dual functions of drainage and irrigation. The population of the Basin is

iIT-2 estimated at 14,300,000 with a large concentration within the Plain of East Semarang.

Mean annual rainfall in the basin averages between 2,000 mm and 2,500 mm. Maximum rainfall occurs during the west monsoon season, generally from October to April and the minimum rainfall occurs during the east monsoon season from May to September. The mean annual tempera­ ture in the lower elevations of the basin is about 260 C with only minor variations throughout the year. Relative humidity ranges from a high oF 90 percent during the west season to a low of 45 percent during the dry season.

IIi.l.4. Description of Project Area

The Jragung and Turitang Rivers sub-basin is located in the eastern sector oF the Plain of East Semarang and comprises about 450 km2 in area. The population of the basin lowlands is about 330,000. It is intersected by a complex system of rivers, drains and irrigation canals with the main rivers being the Penggarop, Dolok, Jragung and Tuntang. The Plain of East Semarang is bounded on the west by the Banjir Canal, on the -iorth by the Java Sea, on the east by the Tuntang River and on the south by the foothills to elevation 30 m above mean sea level (MSL). Th( rivers originate in the volcanic highlands of the Ungaran Volcano and Flow in a northerly direction into the Java Sea. The drainage system in Lhe Jragung-Tunl-ang Rivers sub-basin includes the following principal water courses:

ragiung River

B-1 River B-15 River (secoindary drain) Cabean River Wonokerto River

I11-3 Tun tang River

Tuntang River Main Channel

The principal communities within the project area are Demak, Guntur, Karangtengah, Gubug and Glapan. These together with numerous small agricultntre communities comprise a population of about 200,000 inhaDitants. Practically all the area within the project is inten­ sively developed for agriculture.

111.1.5. Existing Improvements

The natural water courses within the Plain of East Semarang have been improved for irrigation and drainage purposes since the middle of the 19th century. New drainage canals were constructed to serve this dual purpose. In 1893 a masonry dam (Bandung Putiangadi) was constructed on the Penggaron River and in 1915 a weir (Bendung Barang) was installed in the Dolok River. The Guntur and Jragung weirs located within the Jragung River system were constructed in 1931 - 1932. The Glapan Weir on the Tuntang River was constructed in 1859. The dikes forming the Tuntang River floodway were constructed over a long period of time with the most recent raising and strengthening of the dikes having been accomplished in 1945. While the deepening and channel rectification work improved drainage conditions, the primary purpose of these improve­ ments was irrigation, with flood control only a secondary purpose. Channel rehabilitation work in the eastern sector of the Plain of East Semarang contLuICes to this date. In 1977, implementation of a plan for channel improvements on the Jragung River system, designed and undertaken on the assumption that Jragung Dam would be constructed, was initiated with the enlargement of certain reaches of the Wonokerto, Gemboyo and B-15 channels. Scheduled completion date for the ongoing work on time Jragung River System is presently estimated at 1981.

I I T-1i 111.1. 'mentation

['ie, naissance and observation indicate that the Jragung- Tuntang R.v_ ub-basin is a heavy producer of sediment. Moderate to heavy siltation is evident in existing drains, rivers and irriga- Lion canals. Thore exist three distinct zones oA: sedimentation in the project area (see Figure 111-2): the upland zone, river flood plain zone ai J..ittoral marine zone.

ThU upland zone sediments were deposited as bed load during the recession period of historical floods. The average depth of river bed deposits is from 1 to 2 w. Locally, scour basins are reported as deep as 25 meters; however, such depths of scour are considered very rare. The tertiary sediments throughout the river systems are actively being doinicut.

At about El. 18.0 m, where the rivers enter the flood plain, sedimentation continues to be influenced by the buried folded marine sediment for distances ranging from 2.5 to 15 km. The gradient in this zone appears tc be sufficient to sutain direcion and the streams are close enough together to be restricted laterally. Of the two main streams only the Tuntang River exhibits sufficient energy to alter direction during flood flows resulting in a meander pattern across its flood plain.

The littoral zone e:hibits seawa'd movement of the shoreline. The streams turn at the zonal hinge line and flow coward the sea in a notherLy direction perpendicular to the coast. The sediments in tihe littoral zone are probably col oidal clays and fine particulate or,anics wh ich coaoulate and settle as a reuult of saliniLy changes wi tLIn tihe Lidal pri sm. Thes'u sediments normally form highly reducing conditions which generate sulFur dioxide resulting in the formation of pVLit, cV'VSLadIs in thme soil.

II 10 The flood plain of the Tuntang River has been filled with several meters of sediment since the flood control levees where built. Based on a survey of the floodway of the Tuntang River conducted in 1972, the depth of deposited sediment above an assumed natural ground eleva­ tion ranges from 1.5 to 3.5 m. This ranslates into a volume of 33,730,000 in3 of sediment deposited in a reach of floodway of about 110 km. Sufficient data are lacking on which to base more accurate determinations of the sediment deposition characteristics of the Jragung and Tuntang Rivers. More detailed studies are required to enable pre­ diction of sediment transport and depesitional patterns that would result from river closures through the construction of dams in the upper reaches of the two rivers.

11.1.7. Flood Problems

Except in some isolated reaches, the existing channels of the Jragung River .-sys tent are inadequate to contain and pass peak discharges having a freqiuency of occurrence of once in 5 years. Overtopping of the river banks cccurs every year on the Jragung River between the weir and the Floso diversion structure and in the area north of the Semarang - Gubug Road. Dcwnstream of the Floso structure, the Jragun's flood carrying capacity diminishes considerably. hlowever, construction of channel im­

provements33 on the B-1 River in 1973 increased tile drainage capacity from about 5 m is -to about LO m3Is. This increased channel capacity is con­ sidered insufficient and overtopping of banks occurs frequently. The area between the Jragung and Tuntang River south of thu Semarang - Gubug Road is regularly inundated by floodwaters from the Tengah and Renggong Rivers and froom overflows from the Tuntang River at the groto Spillway. Flood 'lows in this area drain very slowly and eventually are collected into the JUagung, 13-I, 13-15 and Gemboyo Rivers for drainage to the sea. 'The e-ist :,glevees on the Tuntanf River form a floodway ranging in widtLh from 170 m to 730 in whicii was once capable of carrying substantial flood flows. lowever, hieavy siltation on the berms (forelands) and in

I I I-(; the river channel has impaired severely the river's hydraulic capacity. In the upstream reach of the Tuntang at 14groto just downstream of Claplan Weir, no levee exists for a distance of about 2 kin, so that flow:: larger than 250 m3 s are pairtially spilled at that point. It has been reported that thme Tuntang River channel is adequate to contain the 1 in 20 year' frequency flood. Frequent overtopping of the banks of the Jragung River and its tributaries with its consequent deposition of sediment has cteated a perched condition of the channels which further impedes proper drainage. Existing channel capacities are shown in PigurC III-1i. It is estimated that approximately 5,000 ha of land in the eastern sector of the Plain of East Semarang are inundated yearly with more extensive flooding occuring at greater intervals. Figure 111-3 shows generally the areas inundated yearly and the maximum flooding that occured in 1977. Recent rehabilitation work on the Gemboyo and Wonokerto rivers has alleviated flooding in the area south of the Semarang - Demak Road.

iIi-'/ 111.2. BASIS 1OR DESIGN

111.2.1. Surveys

The basic data for preliminary designs of tile channel improvement plans contained in this report were derived from existing Topographic maps to scales of 1:10,000, 1:100,000 and 1:250,000. These maps were supplemented by recent Topographic surveys of tile Jragung River system consisting of pians, profiles and cross-sections originally developed for design of the on-going construction work under Plan 1. On the Tuntang River, 18 cross-sections taken in August 1972 and covering the reach from the Java Sea upstream to Gubug were supplemented by 6 more cross-sections obtained by field surveys conducted in July 1979. A total of 21L cross-sections on the Tuntang River were used to develop center-line profiles for design studies extending from the Java Sea to Glapan Weir. Structure sections of mojst of the major irrigation and drainage structures such as Jragung, Guntur, Ploso and Gl-apan Weirs were available for the design studies together with plans of some of the major road and railroad bridges. These data were further supplemented by field obse:rvation and inspection. Vertical control is referred to Sea Level Datum (5.p.13.).

111.2.2. loils

Soils adjacent to the river channel in the upper reaches of the project (upland zone - Figure 111-2) consist of gravel and sand, silt and clays deposited as bed load during the recession period of historical floods. These deposits form river terraces that range in height up to a maximum of 10 meters above the river invert. The soils in the river' flood plain :zone consist generally of fine sands, silt and clays. Further downLstream, within the littoral zone, the soils are predominantly dense, oirganic clays. The foundation soils for the proposed levees and coii:_:truc ted herm.; consist predominantly of f.ine sands, silt and clays.

1.11-8 f'eld explorations and soil mechanics analyses are lacking and will be required during the detailed design stage of the project for stability analyses of the embankmients and to determine foundation conditions for design oF major structures.

I 1.J2.3. Hlydrau.c Design

Project design flows for the Jragung and Tuntang Rivers for the with and without dam conditions and for two levels of protection (I in 20 year and 1 in 50 year levels) are contained on Table III-1. The peak discharges range from a minimum of 185 m3/s to a maximum of 950 m3/s depending on the reach of river and the conditions set for each of the alternative plans.

Statdard procedure is -to use a l-in-20 year level of protection as basis for design of flood control wor's. However a 1-in-50 year level was also investigated to aid in determining the effect on existing struc­ tuves and to expand the array of alternative plans considered. Since at the time of making this study the hydrologic data developed earlier by NIDECO ,;ere available, the same as shown in Table III-1 were used. Therefore, it should be noted that the project floods concurrently being devel~ped by PRC/ECI may be somewhat different from those used in this study. However, the differences between the two are expected to be insignificant.

Water surface profiles and determination of channel dimcnsions to contain the selected project design flows were accomplished by the use of Manning's equation for tranquil flow conditions assuming an energy gradient equal to the invert gradients. Roughness Coefficients ("n" values) used in the hydraulic computations are as follows:

I1]-9 Main channel flow:

110 = .025 for velocity considerations 1111 = .030 for capaciLy considerations

Overbank Clcw :

"111 = .040 - .050

Selection of the above "n" values for hydraulic computations is predicated (n proper future maintenance of the improved channels to obtain, insofar as is practicable, conditions that would prevail on completion of construction. The topography of the area controlled in a general way Lhe selection of channel alignment and. invert grades. Channel ifiv-trI grades were selected giving due consideration to such Factors ai: existing elevations of weir structures, rcad and railroad bridges and minimizing excavation to a reasonable degree. Another im­ portant factor in the selection of design invert grades and depths of Flow is tLhe allowable maximum unit tractive force design value for unl.ned earth channels taking into consideration the characteristics oF t:lie bed materials within the project area. A maximum design value o[ 25 N/m2 has been adopted by the Proyek Jratunseluna staff, based on their experience in Ieslign and construction of irrigation and drainage works. The preliminay hydraulic designs outlined in this report are based on a un i.t tractivo 1lorce equal to or less than 25 1/12 for the design d[:clarges.

.... 1. Al ternative Plans Cons idered

The construction of dams and reservoirs in the upstream reaches of tile Jrarig and 'luittdnig Rivers will only partially alleviate the flood ,1id dh'ainlgol poblemin .w1 t:he Plain of East Semarang. As stated in ct.i.oll J I I . .7 , tLhe downs tream channels are inadequate, in their p)Inr !onlt conidi Lion, to drain all flool flows caused by heavy local

.I111-10 rainfall and the run-oFf originating in upstream tributaries. In the absence of the flood control reservoirs on the system, channel enlarge­ ment and construction of levees are the usual measures adopted for providing a reasonably high degree of flood protection.

It should be noted that under normal circumstances the measures recommended to control the floods are either any one or a combination of channel improvemeint, levee construction and building of retention/ detention reservoirs. If one of these measures cannot be adopted due to physical, financial or other constraints, then reliance has to be made on the next best alternative. However, flood control reservoirs on the system are always preferred because these trap the excessive sediment loads from the upper parts of the basin which otherwise would choke up the drainage channels and irrigation channels in the lower flood plains. In the case of the Jragung and the Tuntang Rivers, even if dams are built at the available storage sites to attenuate the flood peaks, the overflowing of the existing river banks cannot be completely eliminated. Therefore, the only way flood mitigation can be achieved on these systems is either -to improve the channels or to build the levees or a combination of the two whichever turns out to be cheaper. Of course, if upstream storage reservoirs are built, 'then 'the need of the said measures would be much less than without the reservoirs. All alternative plans considered involve the construction of unlined earth 'trapezoidal channels, drop structures and levees generdlly fol. wing the alignment of existing streams. The proposed conceptual plans are described in tiLe following paragraphs.

111.2.5. Description of Proposed Plans

A brief description of the seven alternative proposils for channel improvements on the Jragung and Tuntang Rivers is given below. Pertinent data on project d(esign flows and conditions considered for each of the plan is contained in Table III-1.

TI [-11 Plan 1. Design and construction of this plan is based on the assumption that Jragung Dam will be constructed and in operation. Channel improvement work is limited to the Jragung River system with no work contemplated for the Tuntang River. The project design flows are based on a frequency of occurrence of 1 in 20 years and range from peak discharge of 185 m3/s just below Jragung Weir increasing to 435 m3 s at the downstream end of the project. The increase in peak discharges in the ((ownstream direction is due to tributary inflow. Design bottom widths of the trapezoidal channels vary from 8.0 m tc 145.0 in,while design velocities range from 2.75 m/s to 1.53 m/s. Construction of two drop structures on the Cabean River are included in the plan. Plan 1 is the presently adopted plan that is under construction with channel enlargement and levee construction having been accomplished in certain reaches of Wonokerto, GCemboyo and B-i rivers. Scheduled completion date for the work on the Jragung River system under Plan 1 is 1981.

Plan 2. It is based on the assumption that Jragung Dam will not be constructed. The project design flows are increased with a consequent increase in channel dimensions. Design flows are based on a frequency of occurrence of 1 in 20 years and range from 480 m3/s to 730 in3/s. Design bottom widths of the trapezoidal channels vary from 55.0 m to 148.0 m and design velocities range From 2.30 m/s to 1.10 m/s. Construc­ tion of one drop structure on the Cabean River and one on the Jragung River below its confluence with the Padang River is included in Plans 2, 3 and N.

Plan 3. This plan is based on the assumption that Jragung Dam will be constructed. Channel improvements and levee construction on the Jragung River system are based on project design flows having a frequency of occurrence of 1 in 50 years. The major difference in the basis for design between Plans 1 and 3 is the greater level of protection afforded the project area. Design peak dischar es range from 220 in3/s to 520 in3/s. Design bottom widths of the channels vary from 214.0 in to 105.0 in and

IA1-12 and design velocities range from 1.10 m/s to 2.11 m/s. As described above, two drop structures are included in Plan 3.

Plan 4. This plan is basically the same as Plan 3 with the excep­ tion that the assumption is made that Jragung Dam will not be constructed. Project design flows are increased wJ.th a consequent increase in channel dimensions and required modifications. Design flows are based on a frequency of occurrence of 1 in 50 years and range from 540 m3/s to 860 m3/s. Design bottom widths uf the channels vary from 62.0 ito 174 inand design velocities range from 1.12 m/s to 2.32 m/s. Two drop structures are included in Plan 4.

Plan 5. It "nvolves channel enlargement and rectification and levee construction on the Tuntang River floodway based on project design flows with a frequency of occurrence of 1 in 50 years. It is further based on the assumption that Gunung Wulan Dam on the upper Tuntang River will be constructed and in operation. The 50-year project design flow used as a basis for design for the levee and channel work is 400 m3/s. Design bottom widths of the channels vary from 57.0 m to 118 m and design velocities range from 1.00 m/s to 1.85 m/s. No drop structures are contemplated on the Tuntang River.

Plan 6. This plan is basically the same as Plan 5 with the excep­ tion that the assumption is made that Gunung Wulan Dam will not be con­ structed. The 50-year project design flow used as a basis for design for the levee arid channel work is 680 m3/s. Design bottom widths vary from 98.0 m to 201 m and design velocities range from 1.00 m/s to 1.92 m/s.

Plan 7. The major feature of this plan is the construction of a diversion channel combining 50-year frequency peak flows of the Jragung and Tuntang Rivers at a point about 7 km below Gubug on the Tuntang River. Tile wide floodway of the Tuutang River system lends

IL1-13 itself to consideration of a plan of channel improvements for draining off to the sea the high flows that would develop in case neither the Gunung Wulan nor the Jragung Dams are constructed. The diversion form the Jragung River would be at a point just upstream of the Ploso struc­ ture and would follow a northeasterly alignment to connect with the Tuntang River floodway at a point about 7 km downstream of Gubug. A flow of 450 m3/s would be diverted from the Jragung River near Ploso for a combined flow in the Tuntang liver below the Junction of the diversion of 950 m /s to be drained to the sea. The Jragung River system below Ploso would be able to carry the lesser peak discharges with a minimum of channel improvement and structure modifications work. The diversion channel would intercept the B-1 and B-15 drains necessitating construction of inlet structures to drain that area south of the diver­ sion channel. A pumping plant at the junction point of the diversion channel and the Tuntang may also be necessary to keep ponding in the area to a tolerate minimum, while construction of a left bank levee on the Tuntang 2 ]I:in length at the Ngroto Spillway area would also diminish flood flows that would require to be evacuated by the inlet structures or pumping plant. Des qn bottom widths of the channels vary from 70.0 m to 281.0 m and velocities range from 1.0 m/s to 2.08 m/s. Plan 7 is based on the most extreme conditions insofar as peak discharges and non­ construction of dams is concerned. The required widths of channels are greater than for the other plans. This may require levee setbacks in some isolated instances.

Adequate topographic maps to study this plan in more detail were not available. Therefore, at this time it is presented only as a concept which should be studied in full detail before the plan could be con­ sidered for implementation.

TI 1-11 111.2.6. Design of Levees

The channel improvement plans outlined herein require construction c,- main-line levees to obtain an increase in the hydraulic capacity of the floodways and to keep required channel widths and depths to a reason­ able minimum. The levee,; will have a crown width of 5.0 m, 1 vertical to 2 horizontal lanidslide slopes and 1 vertical to 3 horizontal water­ side slopes. The flatter waterside slopes will provide a wider base to improve the stability of the embankmient and would be moroe resistant to erosion during high flows. Standard levee and channel sections are shown on Figure 111-5. Construction of the levees and berms would be accomplished by utilizing channel excavated material compacted to a pre-determined density. The levee section will be constructed about 0.3 inabove the final design grade to provide for future consolidation and settlement of both the levee embankment and its foundation. Maximum height of levees is about 5.0 m. This indicates that in the lower reaches of the rivers where foundation conditions are poor, stability analyses will be required for final design. A freeboard allowance of 0.5 m above the design water surface will be provided on all levee construction. An all weather road consisting of a 10-cm thickness of crushed mineral aggregate 4 m wide will be provided on all levee crowns to facilitate maintenance operations and for patrol and inspection purposes during periods of high flows.

111.2.7. Design of Channels

Capacity determina Lions for the flood control channels investigated for this report are based on the project design flows shown in Table III-1. All alternative plans involve construction of an unlined earth trapezoidal channel following generally the alignment of the existing streains. The channels will have a 1 vertical to 2 horizontal side slopes and will vary in width depending on hydraulic capacity requirements.

111-15 Standard levee and channel sections for the Jragung and Tuntang Rivers are shown in Figure 111-5. Cnter-line profiles ,)f the ,ivers are shown in Figure 111-6 and 111-7. Berms will be constructed utilizing the excess material excavated from the channel. This will allow a certain amount of erosion that may be caused by river migration and for protection of levee embankmnents during moderate to high flows. Construction of berms will be from channel excavation and compaction requirements will be the same as for levee embankqents. The berms will be a minimum of 4.0 m wide and will have a finish grade sloped at least 1.0 percent to drain toward the channel when high flows recede. It is anticipated that channel excavation will result in an excess of material over and above that required for embankments. The excess material may be placed land­ ward of the levees to serve as a seepage berm in reaches where seepage may be a problem. On the Tuntang River excavated material may be slabbed on the landside of the existing levees where this would not interfere with existing irrigation or drainage ditches. The material may also be utilized to flatten waterside slopes to provide greater stability to the embankments. Low-lying areas within economical haul distances will be identified for use as spoil disposal sites.

111.2.8. Drop Structures

The four alternative plans for channel improvements on the Jragung River System include provisions for construction of Lwo drop structures; one on tile Cabean River at approximately km 26.5 and one on the Jragung River at approximately km 33.5. The drop structures are required to control the effective gradient of the river by limiting invert slopes to obtain non-erosive velocities. llydraulic design of the drop struc­ tures will involve consideration of weir length for a given discharge and design of the overpour basin to dissipate the energy developed by the drop. The structure will be designed to preclude flanking. Con­ sideration will be given during final design to the possibility of installing a folded-weir type drop structure that will not require

II1-16 a permanent pool for energy dissipation. This type of structure was developed by Dr. H.A. Einstein, University of California at Berkely, for the Department of Agriculture, Soil Conservation Service. Instal­ lation of folded-weir type structure will preclude periodic removal of sediments that would be required if a conventional stilling basin design is adopted.

111.2.9. Structure Modifications

The proposed widening and deepening of existing channels required under all alternative improvement plans will involve the modification, extension or complete reconstruction of numerous major and minor existing structures located along the alignment of the rivers. Modifications will be required for irrigation and drainage inlet structures, weirs, control structures and road and railroad bridges. A list of the major struc­ tures is contained in Table 111-2.

111.2.10. Interior Drainage

A system of secondary drains will be provided to collect interior drainage that will include inlet structures through the levees located at appropriate intervals designed to drain run-off into the main flood control channels. The interior drainage will be designed to handle a 1 in 10 year frequency storm. Detailed topographic data will be required to design a layout of the drainage system. It is anticipated that placement of excess excavation material obtained from required channel excavation will aid drainage by eliminating excessive ponding in existing low-lying areas.

111.2.11. Cost Estimates

Preliminary ertimates of cost of the seven alternative plans are presented in Table TTI-3. The estimates are for planning purposes E.nd

T 1E-1.7 include construction and righits-of-way (exploration) costs to aid in making relative cost comparisons between the several alternative plans.

At the present level of the study, detailed operation and maintenance cost have not been evaluated. However, for planning purposes, the same may be considered ac 1 percent of the capital costs, per year.

111.3. OPERATIONS AND MAINTENAICE

It is anticipated that the project area will be organized into a levee or flood control district hiving an organizational structure that would serve the needs of area residents. The districts would be responsi­ ble for conducting the business affairs, management and operation of the project area insofar as flood control is concerned.

Physical operation and maintenance of the project works would be performed by a work force o. technicians and laborers whose duties would be to maintain the flood control levees and channels at their designed operational state and to maintain, repair and operate drainage and other appurtenant structures. A standard operation and maintenance manual would be prepared to guide district personnel in the performance of their duties. The present organization of the Public Works Depart­ ment could be expanded to include the flood control districts discussed herein.

IIT-18 111.4. CONCLUSIONS AND RECOMMENDATIONS

111.4.1. Conclusions

On the basis of the results of studies made during this investiga­ tion and the data presented herein, it is concluded that: a) a serious flood problem exists in the lower reaches of the Jragung and Tuntang Rivers project area and .) that from an engineering standpoint, it is feasible to undertake a flood control plan that will provide a high degree of flood protection to the project area. Irkwever, it is antici­ pated that factors other than engineering feasibility will be given equal consideration in the final selection of the optimum basin plan. The other principal factors to be considered are economic feasibility, effect on total overall basin planning and environmental and social effects.

111.4.2. Recommendations

It is recommended that a plan for flood control be adopted that will provide a reasonably high degree of flood protection to the project area and that would be responsive to the objective established for the overall basin plan. It is further recommended that, prior to initiating more refined studies of the selected plan, the following minimum data be developed for use in such studies:

III.4.2.a. Hydrology

Develop frequency curves for both rivers for with and without dams conditions. Establish project design flows for hydraulic studies and capacity determinations.

III.4.2.b. Field Data

Detailed topographic surveys from Java Sea upstream to Glapan and

11 -19 Jragung Weir to include horizontal and vertical controls, cross sections, pL,ofiles and sections at existing structures.

Controlled aerial photography

Soils exploration (and laboratory testing) at appropriate intervals along the alignment of the proposed levees and at locations of major structures.

111-20 TABLE i!I-1

FLOOD CONTROL DRAINAGE - ALTEFNATIVE PLANS

DESIGN DISCHARGES m 3 /s

Stream Reach 1 in 20 years 1 in 50 years *Jragung River *Jragung River Tuntang River Jragung-Tuntang With Dam Without Dam With Dam Without Dam With Dam Without Dam Combined With Gunung Wulan Diversion (Plan 1)- (Plan 2 (Plan 3) Channel (Plan 4) (Plan 5) (Plan 6) (P-n 7)

Jragung River: Weir-Padang 185 480 220 540

Padang-Ploso 245 540 295 635 - Cabean: Pioso-B-! 245 540 295 635 B-I: Cabean-B-!5 350 645 420 760 Gembovo:

B-15-Wonokerto 435 730 520 860 Wonokerto: Gemboyo-Sea 435 730 520 860

Tuntang River: Glapan Weir - Sea - _ - - 400 680 - GlaDan Weir - Diversion - 680 Diversion - Sea - 950

Reference: NEDECO Report July 1979 Consequences of the postponement of the 11JT7u_ a=ung n Dam".a, TABLE 111-2

LIST OF MAJOR EXISTING STRUCTURES TUNTANG/JRAGUNG RIVERS

Type Required Length - M Profile SFa of Plan Plan Plan Plan Plan Plan Plan Structure 1 2 3 4 5 6 7

JRAGUNG RIVER ,YSTEM:

C 10.00 Rd. Bridge 95 168 125 194 - 10.02 Rd. Bridge 95 168 125 194 - - - 0 . o 13.03 Rd. Bridge 65 121 91 139 14.77 Rd. Bridge 65 121 91 139 - - - 15.23 Rd. Bridge 65 121 91 139 - - -

19.06 Guntur Weir 57 109 77 125 - - - , 29.40 Rd. Bridge 37 37 45 45 - - 77

29.90 RR. Bridge 37 37 45 45 - - 77

0 29.55 Rd. Bridge 41 77 50 87 77 C-)32.20 Ploso Str. 42 77 50 87 - - - (Jragung) 32.40 RR. Bridge 42 82 53 94 - - -

TUNTANG RIVER:

14.45 Rd. Bridge - - - - 116 185 255

14.50 RR. Bridge - - - - 116 185 255

42.00 Rd. Bridge - - - - 70 105 105

46.00 RR. Bridge - - - - 70 105 105

111-22 TABLE 111-3

FLOOD CONTROL AND DRAINAGE ESTIMATE OF COST

Plan No. Construction Expropriation Total First Cost _ Rp Rp Rp

1 7,521,250,896 473,768,800 7,995,019,696

2 12,963,014,926 420,940,000 13,383,954,926

3 9,876,046,726 218,900,000 10,094,946,726

4 13,740,842,100 572,260,000 14,313,102,100

5 10,208,576,356 746,680,000 10,955,256,356

6 20,648,177,210 1,238,680,000 21,886,857,210

7 27,580,907,511 1,579,920,000 29,160,827,511

111-23 BIBLIOGRAPHY

No. Title

1 NEDECO. Jratunseluna Basin Development Plan, Main Report, Conclusion & Recommendations. November 1973.

2 NEDECO. Jratunseluna Basin i)ev'lopment Plan, Supporting Report I, General Information. July 1973.

3 NEDECO. Jratunseluna Basin Development Plan, Supporting Report IV, Geology and Soil Mechanics. July 1973. Part A Text Part B2 : Figures.

4 NEDECO. Jratunseluna Basin Development Plan, Supporting Report V, Dams. July 1973.

5 NEDECO. Jratunseluna Basin Development Plan, Supporting Report VIII, Salinity Aspects. July 1973.

6 NEDECO. Jratunseluna Basin Development Plan , Glapan Dam - Irrigation, Flood Control & Hydropower Project, Feasibility Study Vol. I, Main Report. July 1975.

7 NEDECO. Jratunseluna Basin Development Plan Central Java, Glapan Dam - Irrigation, Flood Control & Hydropower Project, Feasibility Stuidy - Vol. 2 - Appendices I - IX, Part A-Text. July 1975.

8 NEDECO. Jratunseluna Basin Development Plan Central Java, Glapan Dam - Irrigation, Flood Control & Hydropower Project, Feasibility Study - Vol. 2 - Appendices I - IX, Part B: Tables, Annexes and Figures. July 1975.

9 NEDECO. Jratunseluna Basin Development Plan Central Java, Glapan Dam - Irrigation, Flood Control & Hydropower Project, Feasibility Study Vol. 3, Supporting Data. July 1975.

10 PRC/ECI. Jragung Dam Multipurpose Irrigation Flood Control & Industrial Water Supply Project, Upgraded Feasibility Report. December 1976.

11 NEDECO. Jratunseluna Basin Development Plan, Supporting Report II, Surface Water Resources.

12 NEDECO. Jr-.tunseiuna Basin Development Project, Feasibility Study, Water Resources Development, Jragung, Dolok & Penggaron Basins, Vol. I, Report. December 1971.

III-24 BIBLIOGRAPHY (Cont.)

No. Title

13 NEDECO. Jragung Dam Flood Control & Irrigation Project, Feasibility Study. August 197j.

14 NEDECO. Jratunseluna Basin Development Plan, Supporting Report VI, Flood Control in the Coastal Plains. July 1973.

15 NEDECO. Jratunseluna Basin Development Plan, Supporting Report VII, River Morphology. July 1973.

16 PRC/ECI. Jragung Dam Project, Final Design Report. April 1979.

17 NEDECO. Consequences of the Postponment of the Jragung Dam. July 1979.

111-25 PRC ENGINEERING CONSULTANTS, INC. -N.. v ...... 1..Z. 7

Z -7 LEGEND . , ,;

RAILROAD ., . . ,. HIGHWAY - - , -. SECONDARY ROAD , pvr,a . -. , " JRATUNSELUNA BASIN . PROJEC1 BOUNDARY SERANG ESTIMATED 41/, ..­ RESERVOIRS - NET PRIG'"8LE". .-. ",,., 3.

A 3 6 0_EXISTINGCho; . , . , .

O UNDER STUDY ea

PROPOSED "" / " ,'". IRRIGATICN SERVICE = - "- - - " 4.

AREAS I'

TUNTANG /JRAunG - . / ,..... "" ' - -. • " .,, • ­ ____"__"__"__,___" .. r. 1 "' ______/ ,A..~PE OTH AYARAt4\ ~'Y.4 R ~' " -JRAGUNG AND TUNTANG- " "'m " \ " " . " ESTIMATED TOTAL I / ,,.(a,,.... I TaI .I NET IRRIGABLE -o.f - p2,,,,, o , -.- . ' -. * .. " AREAS 34,949 ha - "" "AN SE -f '4AK...... / .

RA" TUNTAKE SERANG '" .".

, , , .4 , ; 1 .. "1114 J U A NA V ¢, . " - : , - <,.,, • ESTIM ATE "" ' -.'46 JRAGUNG " ... 7 ' : . I...... A "'.: .P i -,. , " .." * - . .. .. I SEM"AR""/;'-" - , R IG B f

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SA q, I SED IM N TAT ION

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\ ..."... I - FLOOD CONTROL AREAS

GoT ,.1O- -1, ./ n •c . PRC ENGINEERING CONSULTANTS, INC. FIGURE III-4

SCHEMATIC DIAGRAM

24 100~

t 40 //"AGNG/// UAGNGRIER TNTNG/

EX'INTEGRATED DEVELOPMENT PLAN Fl CAEXISTING CAPACITIES

NOT TO SCALE ,m PRC ENGINEERING CONSULTANTSINC. FIGURE III -5

STANDARD LEVEE & CHANNEL SECTIONS

2 j4m 34m o--.o._/d valir 7Z,/ vors 27 2harles b- -var/es 4

JRAGUNG RIVER SYSTEM AND TUNTANG RIVER BELOW KARANGTENGAH

Existing Channel __Existing

2 2

LbJ var/es

TUNTANG RIVER ABOVE KARANGTENGAH

TUNTANG / JRAGUNG RIVERS INTEGRATED DEVELOPMENT PLAN

STANDARD SECTIONS NOT TO SCALE ",) .5

KA RA NG TE NGAH , .....

UENMTAS*(A NU I _-_

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JRAGLING RIVER SYSTEM-JAVA SEA TO JRAGUNG WEIR. R. LWONOKERTO

. _/-"__-].j - .B - 15 ( SECONDARY DRAIN ).

OS-'.- RR_ - / 2 TUNTANG RIVER - JAVA SEA TO GLAPAN WE;R.

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