Appendix 3 ADB. IN THE 6 CI's RIVER BASIN TERRITORY - PACKAGE B. Final Report B.2 - Strategic Spatial Planning

Transcription

1 ADB TA 7189-INO: INSTITUTIONAL STRENGTHENING FOR INTEGRATED WATER RESOURCES MANAGEMENT (IWRM) IN THE 6 CI's RIVER BASIN TERRITORY - PACKAGE B Final Report B.2 - Strategic Spatial Planning Appendix 3 Upper Citarum Erosion and Sedimentation

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3 FINAL REPORT B.2 Strategic Spatial Planning Appendix 3 UPPER CITARUM EROSION AND SEDIMENTATION TA7189-INO: Institutional Strengthening for Integrated Water Resources Management (IWRM) in the 6 Ci's River Basin Territory - Package B Ministry of Public Works, Directorate General of Water Resources Asian Development Bank

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5 FOREWORD This note concerns part of the extra work for B2 which was proposed in October The objectives of the proposed activities were the following A. Establish the methodology to simulate the peak flow response (sensitivity) of catchments to changes in land-use using a GIS based approach, providing sufficient detail necessary for zoning; followed by application to the relevant catchments in the 6 Cis river basin territory; B. Preparation of zoning synthesis for the upper Citarum basin (upstream of Saguling). The present note concerns component B) with some extra attention to the ranking of rehabilitation measures for the Upper Citarum catchment. Component A is being applied (may 2011) to the 6 Cis river basin territory; the methodology (component A) will be reported in a separate note attached to the application to 6 Cis. page i

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7 TABLE OF CONTENTS Page 1. Introduction 1 2. Assessment of erosion sensitivity and watershed conservation interventions Introduction Erosion sensitivity analysis using USLE Background: soil erosion- and sedimentation process Review of USLE method Influence of cultural- and mechanical management practices 9 3. Change in land-use Erosion analysis (6Ci s project) for Upper Citarum Initial estimate of sedimentation of Saguling reservoir Reconstruction of the past sedimentation process of Saguling and current catchment condition Projection of future sedimentation with current trend Identification of measures to minimize erosion Target for reducing erosion Current land-use in conservation areas Protection of land with slope >30% Upgrading of bush/scrub areas Summary of proposed catchment rehabilitation program Impact of identified measures Ranking of the effectiveness of erosion rehabilitation measures Projection of future sedimentation based on the proposed catchment conservation program Remark on the distribution of sediment in the reservoir: Assessment of run-off sensitivity and runoff protection Runoff and land-use change SCS hydrographs Runoff protection Proposed zoning for erosion- and runoff protection Introduction Setting for water resource zoning Inventory of water zoning requirements Objectives for water zoning Spatial planning process relationship with water resources Land-use classification in spatial planning and relationship to water zoning Proposed water zoning related to erosion and runoff protection Elaboration of the proposed zones for the Upper Citarum Conservation for highly sensitive areas Re-forestation Upgrading of bush/scrub areas expanded conservation zone Protection of bare soil Runoff protection Reflection on accuracy of results, standards and implementation of zoning 41 page ii

8 LIST OF FIGURES Page Figure 2.1. Soil erodibility (Factor K) for Java and Upper Citarum basin 7 Figure 2.2. Rainfall erositivity (Factor R; Bols map) for Java and Upper Citarum 8 Figure 2.3. Slope map for Java (SRTM30) 10 Figure 2.4. Slope length factor LS for Java 10 Figure 2.5. Land-use map for Java (Bakosurtanal 2009) 11 Figure 3.1. Modis 2008 land-use map for Upper Citarum basin 14 Figure 3.2. Modis 2001 land-use map for Upper Citarum basin 15 Figure 3.3. KLH 2009 land-use map for Upper Citarum basin 15 Figure 3.4. Bakosurtanal 2009 land-use map for Upper Citarum basin 16 Figure 3.5. Slope classes for Upper Citarum basin 16 Figure 4.1. Reconstructed sedimentation process Saguling 19 Figure 5.1. Slope classes for Upper Citarum basin 23 Figure 5.2. Population density in 2000 and 2008 (desa) 24 Figure 5.3. Impressions from dry land agriculture with plenty of bare soil 25 Figure 5.4. Impression of well managed dry land agricultural activity (site in Cisangkuy sub-basin) 25 Figure 7.1. Topographical profile of the Upper Citarum basin 30 Figure 7.2. Runoff pattern (SCS hydrographs) for typical watershed for different land-use (curve numbers) 32 Figure 8.1. Water zoning in spatial planning 34 Figure 8.2. Erosion sensitivity for low (map above)and high management (map below) 37 Figure 8.3. Areas (slope >30%) considered for re-forestation 38 Figure 8.4. Areas (slope >30%) considered for re-forestation 39 LIST OF TABLE Table 2.1. K-factors for the different soil types of Java 6 Table 2.2. Slope length for different slope classes 9 Table 2.3. Summary of cultural management practices 12 Table 2.4: Summary of mechanical management practices 12 Table 2.5: Management practices for irrigated rice and estate production 12 Table 2.6.Management factors for non-irrigated agriculture for different management levels 13 Table 2.7. Management factors for estates and plantations for different management levels 13 Table 2.8. Combined land use/management factors of natural and production forests and scrub 13 Table 2.9. Combined land use/management factors for grass lands for different management levels 13 Table 4.1. Characteristics Saguling reservoir storage 17 Table 4.2. Estimation of sediment generation for different land-use maps and management levels 18 Table 5.1. Land-use in the different sub-basins 21 Table 5.2: Land-use in spatial planning conservation areas 22 Table 6.1. Estimated erosion (Mton/year and ton/year/ha)) of the 8 sub-catchments 27 Table 6.2. Efficiency of sediment reduction measures for different land-uses in different sub-basins 28 Table 6.3. Potential sediment reduction for different land-uses in different sub-basins 28 Table 6.4. Best measures to realize the target reduction of sediment input to Saguling 28 Table 8.1. Classification of zoning in the New Spatial Law (UU Nr 26/ page iii

9 1. INTRODUCTION Water resources in the Upper Citarum basin (upstream of Saguling dam) face strong challenges associated with the alarming rate of sedimentation of Saguling reservoir and flooding in the Bandung valley. Sedimentation of Saguling reservoir will strongly constrain the highly valued functions of the reservoir, and sedimentation of the main Citarum river channel in the Bandung valley contributes strongly to the flooding problems. The degraded condition of the catchments, caused by a rapidly expanding urbanized settlement and encroachment of settlement and agricultural activities in sensitive catchment areas, forms a major cause of the problems. A rehabilitation of the catchment will be necessary to establish a desirable catchment status, as well as zoning (to be implemented in the spatial plan) to secure a long term sustainability. Basic to identifying rehabilitation measures, as well as defining zoning, is an assessment of the sensitivity of the area of influence for the problem(s) at hand. For erosion/sedimentation this concerns the sensitivity of the catchment for erosion derived from catchment characteristics, and for flood control the influence of particular upstream areas and its land-use on the magnitude of the downstream flood. The present note elaborates on those sensitivity analyses, and their use in the specification and ranking of rehabilitation measures, and the preparation of zoning. Section 2, reviews erosion sensitivity analysis using the USLE method. Section 3, identifies and discusses land-use change in the Upper Citarum basin. Section 4, presents a reconstruction of catchment condition and sedimentation of Saguling over the last 3 decades (since construction of Saguling) and projection of future sedimentation based on the current trend. This is followed in Sections 5 and 6 with an identification of rehabilitation measures and assessment of their impacts, and efficiency ranking in dealing with the sedimentation problem. Section 7, elaborates on the runoff sensitivity in the steep upstream sub-catchments. Section 8, proposes a set of zoning for erosion- and runoff protection. Section 9, concludes this note with a reflection on the availability of data and accuracy of the analyses, - the need for standards, and - incorporation of water zoning in spatial plans. page 1

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11 2. ASSESSMENT OF EROSION SENSITIVITY AND WATERSHED CONSERVATION INTERVENTIONS 2.1. Introduction Sedimentation of Saguling is progressing in an alarming rate, threatening the functioning of the reservoir in the longer term, and starting to influence the turbines as sediment filling is approaching the dead storage. In the present note an assessment is made of erosion and sedimentation process of Saguling, leading to an estimate of the present condition, as well as an inventory of watershed management measures and their influence on the further sedimentation of Saguling. The methodology is based on the work of Hamer in the early 1980 s at IPB and the further referencing and application in the BTA-155 project (1988). A GIS model for estimation of potential catchment erosion in function of management measures has been created in cooperation with IPB; this includes as special feature the possibility to introduce various watershed management measures; the classification of these measures and their impact is based on the work of Hamer at IPB in the early 1980 s Erosion sensitivity analysis using USLE Background: soil erosion- and sedimentation process Basic processes Soil erosion has many ecological and economic consequences. The productive top-soil is removed and the soil productivity deteriorates, landslides and gullies reduce the area of productive land and may damage roads and buildings, the hydrologic regimes of the rivers change and increased sediment loads result in eutrophication and the silting up of reservoirs and irrigation structures. Once the environmental degradation has started it can only be stopped with great effort and at considerable costs. The most important factors controlling soil erosion are: rainfall, surface runoff, wind, soil, slope, plant cover and absence or presence of conservation measures. These and other related factors can be grouped under three headings: energy, resistance and protection. The factors grouped under the heading energy include the potential abilities of the rainfall, the surface runoff and the wind to cause erosion. This ability is generally referred to as erosivity. Incorporated in this group are also the factors that directly affect the erosivity such as the reduction of slope lengths by the construction of terraces. In the resistance group the erodibility of the soil is of major importance. It depends on physical and chemical properties of the soil. Infiltration capacity and management of the soil are other factors in this group. Good soil management practices result in well aggregated soils that do not crust, and thus have high infiltration rates. High infiltration rates on their turn decrease the erodibility by reducing the surface runoff. The protection group includes factors related to plant cover. The vegetation intercepts part of the rainfall and reduces the erosivity of the falling raindrops and the velocity of the surface runoff and the wind. The protection offered to the soil depends on the nature of the plant cover, and by changing the land use man is able to change the degree of protection given to the soil. Land use changes and crop management therefore are important tools for soil conservation purposes, other factors are much less easily manipulated by man. From soil erosion to reservoir sedimentation is a process with several phases. It starts with detachment of individual particles from the soil mass and their consequent transport by the erosive page 2

12 agents, such as wind and running water. Next is deposition of sediment on the catchments surface that occurs when the available energy is insufficient for further transport of the detached particles. Transport in the river, which also may include sedimentation (or scouring) follows, with finally the deposition at the end point of the basin in a reservoir or the sea. The impact of falling raindrops is an important detaching agent. Soil particles are thrown into the air and travel over considerable distances. Other processes such as physical and chemical weathering, tillage operations by man and trampling by cattle also contribute to the detachment of soil particles, as do running water and wind. Once the soil is loosened, the detached soil particles can be easily removed by the transporting agents. Two groups of transporting agent can be recognized, the first group comprises those who act evenly over a rather extended area and result in the removal of a soil layer of relatively homogeneous thickness. Examples are rain-splash (splash-erosion), overland flow (sheet-erosion) and wind (winderosion). The second group of agent are those that concentrate their actions in defined channels: water flow in channels that are so small that they can be filled in by plowing (rill-erosion) or in larger, more permanent, features (gully-landslides, creep, etc.) is another form of erosion that is more or less restricted to a limited area. The quantity of material supplied by detachment processes and the capacity of the transporting agent to remove this material determine the severity of the soil erosion. Conservation measures can be aimed at either reducing the detachment, e.g. by maintenance of a protective vegetation cover that reduces the rainfall impact, or decreasing the transport capability of the eroding agent, e.g. by terracing to reduce the velocity of the overland flow. To be able to make an optimal choice between possible conservation techniques, it is important to know whether detachment or transport is the limiting factor in the soil erosion process. In Java wind-erosion is of limited importance. Of the water related soil erosion processes sheet-and rill-erosion are dominant over gully-erosion. Another source of (hard to predict) erosion, viz landslides and mud flows, may contribute considerably to the sediment yield of the river. Sediment Delivery Rate (SDR) Not all the soil loss on the slopes is delivered to the river; generally deposition takes place at various locations in the watershed. The eroded soil that is transported to the river and passes a certain point along the stream channel in a certain period, is called the sediment yield of that river at that point, and is expressed in tons or m 3 per year or tons or m 3 /ha per year. The ratio between the soil loss on the slopes and the sediment yield of the river somewhere downstream in the drainage basin is called the Sediment Delivery Ratio. If the sediment delivery ratio of a basin is known, the effect of soil conservation measures or changes in land use, resulting in changes in soil loss can be translated to changes in sediment yield of the river. Although the concept of SDR is logical and simple, many of the processes involved are not yet fully understood. Sediment sources and sinks may be distributed in various ways over the catchment and large quantities of sediment may be kept in storage in the basin. The SDR depends basically on the same independent variables as the sediment yield. Variables that are often used in the predictive equations are: basin area, relief, total stream length, the bifurcation ratio and the dominant land use. Sediment delivery ratio s range from 1 to 40%, while the majority of the observed values is larger than 5 and smaller than 15. Arif (1986) published sediment delivery ratios that ranged between 5 and 25% for a number of river draining catchments with variable areas on West Java. The Dep of Forestry considers SDR s from 9 to 43 % acceptable. Information on sediment delivery ratio s in other tropical areas is hardly available, on a global scale sediment delivery ratio s range from 3 to 90%. The SDR may change over time (for example by urbanization) as the catchment characteristics change. page 3

13 Review of USLE method The USLE (Universal Soil Loss Equation) has been widely used in Indonesia and is commonly accepted as a good method to establish soil erosion rates and evaluate conservation measures, but the necessary input data are not always readily available. Information is scattered over a large number of institutes, presented at different scales and with different detail, and collected for different areas. The USLE can only be used to calculate long-term averages of sheet-and rill-erosion; gully-and channel-erosion processes are not taken into account. This means that it is only applicable to a limited part of the catchment. For Indonesian conditions however sheet and rill erosion are the dominant processes. The erosion rate in tons/ha are given for a certain soil, with a certain slope, and a given land use and land management, including conservation measures. This erosion rate on the slope cannot directly be translated to an amount of sediment entering the river channel or to amounts of sediment leaving the drainage basin; to connect erosion rates on the slopes with sediment outputs of the river the SDR needs to be applied. The USLE is a mathematic model, used to predict soil losses that result from areal erosion. The equation is designed for conservation planning purposes. The basic equation of the USLE reads as follows: A = R. K. L. S. C. P in which: A = computed soil loss per unit area (ton/ha, when metric units are used) R = the rainfall factor, the number of erosion index units (EI units) in the period of consideration. The erosivity index is a measure of the erosive force of a specific rain K = the soil erodibility factor, the erosion rate per unit of erosion index for a specific soil, in a cultivated, continuous fallow plot, 22.1 m long, on a 9% slope L = the slope length factor, the ratio of soil loss from the field slope length to that from a 22.1 m slope length on the same soil type with the same gradient and the same crop and management S = the slope gradient factor, the ratio of soil loss from the field gradient to that from a 9% slope, on the same soil type, slope length, crop and management C = cropping/management factor, the ratio of soil loss from a field with a specific crop and specific management to that from a fallow slope with the same soil, slope length and slope gradient P = the erosion-control practice factor, the ratio of soil loss from a field slope with conservation practices to that with straight row farming up and down slope, on the same soil type and with the same slope length To be able to use the USLE to estimate the actual magnitude and distribution of the soil erosion in the project area, it is necessary to obtain information on the spatial distribution of the explanatory variables. The various characteristics are derived from available maps, those are entered digitally as overlays in a GIS system. A grid system is further used whereby for each pixel the characteristic values are obtained from the different overlays. The erosion is then calculated for each pixel. The following map layers were used in the present analysis Soil map by Puslitbang Tanah (55 soil types) Land cover: different maps have been used (Modis, KLH) Rainfall erositivity map of Bols (1978) Slope: from SRTM 30m page 4

14 The R, K, L, and S factors comprise physical parameters which can not be influenced by management. Those are described below. The management factors C and P are of particular importance in the present analysis and are discussed in section 2.3. Soil erodibility, the factor K: The vulnerability of a soil to erosion depends to a large extent on the soil physical and chemical properties; the soil erodibility varies with the texture, aggregate size and aggregate stability, organic carbon content and permeability of a soil. Large particles are resistant against erosion, because of the greater force required to transport them. Fine particles, on the other hand, have a high cohesiveness and are therefore resistant to detachment. Least resistant are silts and fine sands. Soils with a high silt content (40-60%) are generally considered to be very erodible. The infiltration capacity of a soil, the maximum rate at which a soil can absorb water, depends on the soil pore size distribution and the pore stability. Well aggregated soils usually have high pore spaces that remain open during wet periods. Excess water is easily transported to the subsoil, and overland flow will only rarely occur; the rainfall intensity will not easily surpass the infiltration capacity and the soil will not become saturated. The organic carbon content of a soil is of importance because of its influence on the aggregate stability, soils containing less than 2% organic matter may be considered erodible. Table 2.1 presents the K-factors for different soils types which have been adopted in the GIS model. Figure 2.1 presents the K-factor on the map of Java based on the soils map for Java. page 5

15 Table 2.1. K-factors for the different soil types of Java Soil type K factor 1 Eutrofic Organic Soils Hydromorphic Alluvial Soils Dark Grey Alluvial Soils Greyish Brown Alluvial Soils Ass. of Grey Alluvial and Greyish Brown Alluvial Soils Ass. of Humic Gleysoils and Grey Alluvial Soils Ass. of Low Humic Gleysoils and Grey Alluvial Soils Ass. of Grey Hydromorphic Soils and Greyish Brown Planosols Greyish Brown Planosols Ass. of Lithosols and Red Mediterranean Soils Grey Regosols Grey Regosols Complex of Grey Regosols and Lithosols Brown Regosols Brown Regosols Yellowish Brown Regosols Yellowish Grey Regosols Complex of Regosols and Lithosols Brown Andosols Brown Andosols Yellowish Brown Andosols Ass. of Brown Andosols and Brown Regosols Complex of Renzinas, Lithosols and Brown Forest Soils Grey Grumusols Dark Grey Grumusols Complex of Grumusols, Regosols and Mediterranean Soils Complex of Brown Mediterranean Soils and Lithosols Ass. of Brown Mediterranean Soils and Grumusols Ass. of Reddish Brown Mediterranean Soils and Lithosols Brown Latosols Reddish Brown Latosols Dark Reddish Brown Latosols Yellowish Brown Latosols Red Latosols Yellowish Red Latosols Ass. of Brown Latosols and Grey Regosols Ass. of Yellowish Brown Latosols and Brown Latosols Ass. of Reddish Brown Latosols and Brown Latosols Ass. of Red Latosols, Reddish Brown Latosols and Lithosols Complex of Red Latosols and Reddish Brown Latosols Complex of Yellowish Red Latosols, Reddish Brown Latosols and Lithosols Complex of Reddish Brown Latosols and Lithosols Complex of Yellowish Red Latosols, Brown Latosols, Yellowish Red Podsolic Soils and Lithosols Yellow Podsolic Soils Yellowish Red Podsolic Soils Red Podsolic Soils Ass. of Yellowish Podsolic and Grey Hydromorphic Soils Ass. of Yellow Podsolic Soils and Regosols Complex of Yellow and Yellowish Red Podsolic Soils and Regosols Complex of Yellowish Red Lateritic and Yellowish Red Podsolic Soils page 6

16 Figure 2.1. Soil erodibility (Factor K) for Java and Upper Citarum basin page 7

17 Figure 2.2. Rainfall erositivity (Factor R; Bols map) for Java and Upper Citarum page 8

18 Rainfall erosivity, the R-factor Soils losses from an agricultural field as a result of a single rainfall storm are, other factors kept constant, directly related to the product of the total kinetic energy of that rain storm (E) and its maximum intensity. Bols (1978) calculated the rainfall erosivity factor for a large number of rainfall stations on Java and Madura and constructed an iso-erodent map. The digitized map of Bols is presented in Figure 2.2. This map layer provides the appropriate R values for the grid cells. Slope length and slope steepness, the topographic factor LS The topographic factors slope length and slope steepness (respectively the factors L and S in the USLE equation) are only treated separately for research purposes. For field applications a combined LS factor is more convenient. The LS factor is an important factor in the USLE, it accounts for more variation in the gross erosion than any of the other factors, except for the crop/management factor. Slope length is defined as the distance from the point where overland flow starts to the point where either the slope steepness decreases to such an extent that deposition occurs, or where surface runoff enters a well defined channel. The effect of slope length on the annual surface runoff per unit area of crop-land is limited, but the soil loss per unit area increases dramatically with increasing slope length. On longer slopes surface runoff increases in velocity and thus in detaching and transporting capacity. In the present GIS model the formula of Wood and Dent (1983) is used, they used the following formula for the calculation of the slope factor. l LS 22.1 m * c * cos * sin in which: l : slope length in m (see table 2) m : = 0.5 for slopes > 5 % = 0.4 for slopes between 3 and 5 % = 0.3 for slopes < 3 % c : = α : slope angle in degrees Table 2.2. Slope length for different slope classes Slope gradient class (%) Slope length l (m) > sin Slope forms a most important input to the erosion computations; Figure 2.3 presents the slope map for Java (from SRTM DEM with 28.5 m pixels). The LS factor and the Bakosurtanal land-use map for Java are respectively presented in Figure 2.4 and Influence of cultural- and mechanical management practices Of particular interest in the present analysis is the use of management practices and there influence on erosion. Hamer (at IPB) (1981) investigated the effects of management practices; this was further elaborated and referenced in the BTA-155 project (1988). Following this reference base two types of management can be differentiated: cultural- and mechanical; those are elaborated below. page 9

19 Figure 2.3. Slope map for Java (SRTM30) Factor C The crop/crop-management factor C describes the total effect of vegetation, crop residues and soil management on the soil loss. The factor is defined as the ratio of soil loss from a field with a particular cropping pattern and management to that of a field with a bare, tilled soil. The factor range from 0 to 1, a value of 0 indicating a 100% protection of the soil against erosion. In the USLE crop cover and management effects are combined in one factor, because they have many interrelationships. Crop residues can be removed, left on the surface or incorporated in the soil, while the effect of the residues management depends on the amount of residue present, which, on its turn, is depending on the type of crop, the soil fertility, the management decisions (e.g. fertilizer input) etc. Figure 2.4. Slope length factor LS for Java page 10

20 Figure 2.5. Land-use map for Java (Bakosurtanal 2009) Factor P The erosion-control practice factor P is the ratio of soil loss using a specific conservation practice compared with the soil loss occurring under up and down hill cultivation. This factor also ranges from 0 to 1. The conservation measures usually included in this factor are contouring, contour strip cropping, terracing and surface mulching. Conservation measures like conservation tillage, crop rotations, residue management etc. are incorporated in the C factor. The effectiveness of conservation practices and thus the value of the P factor generally depends on the slope steepness. For each of the land utilization types and for 4 different slope classes the appropriate management factor can be established, taking into account both cultural and mechanical management practices. Sawah s and estate/plantation crops are treated separately. The management practices are given in Table 2.3, 2.4 and 2.5. The main source for this data is Hamer, page 11

21 Table 2.3. Summary of cultural management practices Practice code Practice level Examples of practices 1 Very low Zero mulch or crop residues removed. No application of manure, composts or fertilizers. No rotation, bare fallow in non crop period. Annual cropping, usually mono-cropping. Very low biomass production per area. No recycling of nutrients, no crop diversity. 2 Low Crop residues burnt on site or surface mulch <0.5t/ha. No application of manure or composts. Few mineral fertilizers. Some crop rotation in response to market. Mixed garden, low density. Inter-cropping, low intensity. Maintenance 20-40% ground cover. Low biomass production per area, nutrients partly recycled. Low crop diversity. 3 Moderate Surface mulch t/ha/year. Application of manure from domestic animal husbandry and household composts. Sub-optimal amounts of mineral fertilizers. Strategic crop rotation, but annual cropping. Mixed garden, high density Intercropping, medium intensity, or if perennials, use of annual inter-crops. Maintenance 40-60% ground cover. Medium high biomass production per area. Moderate crop diversification Moderate nutrient circulation. 4 High Surface mulch t/ha/year, imported if necessary. Application of mineral fertilizers, combined with manure and/or composts. Inter-cropping, high intensity, incorporating perennials. Legumes in rotation 1 year in 4. Maintenance ground cover 60-80%. High biomass production per area. High crop diversity. Intensive nutrient circulation. 5 Very high Surface mulch 3-6 t/ha/year, imported if necessary. Strategic application of mineral fertilizers, composts and manure to maximize production. Inter-cropping, high intensity or mono-cropping, high intensity in strategic rotation Legume in rotation, 1 year in 3. Maintenance >80% ground cover. Very high biomass production per area, high to medium crop diversity. Intensive nutrient circulation and accumulation of nutrients in the system. Source: Hamer, 1981 Table 2.4: Summary of mechanical management practices Practice code Practice level Examples of practices 6 None No applied practice, field boundary effects only 7 Low Colluvial terraces on grass/bamboo or contour strip cropping 8 Moderate < 5% slope: moderate standard permanent grass strips or moderate design graded/contour earthworks with minimal water disposal facility; or, if mechanized, contour cultivation > 5% slope: traditional ridge terrace or: or: low standard (non stabilized) bench terrace narrow outward sloping terraces for permanent tree crops (e.g. rubber, pinus sp.) 9 High < 5% slope: high standard permanent contour grass strips well designed and maintained or: fully designed graded earthworks, or banks, with designed water disposal facility > 5% slope: moderate standard bench terrace (i.e. not graded and without designed water disposal system, but risers stabilized grass or rocks 10 Very high High standard bench terrace with reverse slope, graded length,, front bund, risers fully stabilized and with fully designed water disposal facility Source: Hamer, 1981 Table 2.5: Management practices for irrigated rice and estate production Practice code Practice level Examples of practices 11 Sawah < 5% slope : sawah, irrigated rice 12 Terrace > 5% slope : irrigated rice terrace 13 Low Estate crops : low permanent cover, or inter-cropping 14 Moderate Estate crops : moderate permanent ground cover. Estate crops planted on contour where exceeds 15% slope 15 High Estate crops : high density permanent ground cover. Estate crops planted on contour where slopes exceed 10% Source: Hamer, 1981 page 12

22 Levels of management In order to facilitate selection of a particular level of management, several levels of management were created (Hamer, 1981) based on combinations of management practices. These different levels of management are compiled for different land-use types; the tabulations are presented in Tables 2.6, 2.7, 2.8 and 2.9. The soil erosion rates are given for each of the 4 management options. Option 1 represents a very low level of management, in which cultural management practices are applied to a limited extends and in which mechanical management practices are restricted to very simple measures like strip cropping. This option 1 more or less represents the worst case or the so called potential erosion. Option 2 represents the actual situation, in which some surface mulching is applied and some fertilizers are used, the applied mechanical management practices are low or moderate (traditional terraces). Option 3 represents a relative high level of management, in which cultural management practices are moderate to high (surface mulching, fertilizer application and maintenance of a fairly high ground cover (60-80%) by application of inter-cropping and crop diversification) and mechanical management practices concentrate on terracing, either outward sloping terraces or (non-stabilized) bench terraces. Furthermore it is assumed that all slopes steeper than 40% that are presently cultivated with non-irrigated dry land crops and plantations will be reforested. Management option 4 represents a situation in which the management practices, both cultural and mechanical are optimal for erosion control. This comprises very high rates of surface mulching (>3 t/ha/yr) maintenance of very high ground covers (>80%), inter-cropping and a high crop diversity. Mechanical management practices concentrate on stabilized (reverse slope) bench terraces. Under option 1 and 2 the extraction/rotation rates of the forests are high and the management level of the grasslands is low. Option 3 and 4 are characterized by low extraction/rotation rates in the forest and improved management levels for the grasslands. Table 2.6.Management factors for non-irrigated agriculture for different management levels Management level Management practice code Slope class Management system code 0-2% 2-15% 15-40% >40% Very low 1-3/ ,2,3,4,5,6 Actual 3-5/ ,8,16,20,21 High 3-5/ ,14,17,18,22 Optimal 4,5/9, ,23,24 Table 2.7. Management factors for estates and plantations for different management levels Managemen t level Management practice code Slope class Management system code 0-2% 2-15% 15-40% >40% Very low 13, ,11 Actual 8,9/ ,26,27,29 High 8,9/14, ,30 Optimal 9,10/ ,32 Table 2.8. Combined land use/management factors of natural and production forests and scrub Forest type Extraction rate Slope class 0 2% 2 15% 15 40% Natural High Low Production High Low Scrub Table 2.9. Combined land use/management factors for grass lands for different management levels Management level Slope class 0 2% 2 15% 15 40% Actual (poor) Improved page 13

23 3. CHANGE IN LAND-USE Land-use change can significantly influence erosion besides the influence of management practices as described in previous section. For example, if forest, with a very low erosion rate, changes into another type of land-use then the erosion rate may substantially increase (except if the other type of land-use has a high management). A substantial change in land-use has taken place in recent years in the Upper Citarum catchment. The MODIS maps for 2001 (Figure 3.1) and 2008 (Figure 3.2) illustrate the strong change in landuse, in particular forested area. Forested area decreases from 85,514 ha to 49,588 ha, a decrease of 36,000 ha (35,926). The influence of these land-use changes is taken into account in the erosion calculations presented in next Sections. There is considerable uncertainty on the extent of the remaining forests. The KLH map (corrected Landsat) for 2009 (Figure 3.3) indicates that there is practically no primary forest left, remaining forest is secondary, associated with a high extraction rate. Total forest in the KLH map (2009) is indicated at only 23,000 ha 1. The Bakosurtanal 2009 map (Figure 3.4 used for the present Java-Bali spatial plan) indicates a total forest area of 26,000 ha. In the present analysis the MODIS maps (2001 and 2008) are used to indicate the strong change in land-use; the Bakosurtanal 2009 map is used in the erosion computations in subsequent sections because it has a more accurate classification of the Indonesian agricultural areas. For comparison an erosion potential calculation is also made with the KLH map (2009) Figure 3.5 illustrates the slope classes in the Upper Citarum catchment, the most important parameter in the erosion- and runoff analysis. Figure 3.1. Modis 2008 land-use map for Upper Citarum basin 1 Strong doubts have been expressed about the remaining forest in the Upper Citarum area; individual spot observations (Google Earth) indicate that the remaining forest may be much less and/or of very limited density. The present analysis adopts the forested area as indicated in the Bakosurtanal (2009) map. page 14

24 Figure 3.2. Modis 2001 land-use map for Upper Citarum basin Figure 3.3. KLH 2009 land-use map for Upper Citarum basin page 15

25 Figure 3.4. Bakosurtanal 2009 land-use map for Upper Citarum basin Figure 3.5. Slope classes for Upper Citarum basin page 16

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27 4. EROSION ANALYSIS (6CI S PROJECT) FOR UPPER CITARUM 4.1. Initial estimate of sedimentation of Saguling reservoir For the initial 1980 s assessment of the erosion rate of the upstream Saguling catchment was carried out for the land use at that time; the sediment yield in the river at that time was measured by DPMA. The following results were obtained: Calculated erosion from the catchment: M ton/year Measured sediment yield in the river: 2.7 M ton/year The SDR derived from this is 2.695/27.18 = or 9.9 % The half life time of the reservoir is then computed as follows (BTA-155) Reservoir half life = 443.5/(2.7*1.1*0.95/1.2) = 189 years With Sediment yield in river: 2.7 t/year Sediment specific weight: 1.1 t/m3 Sediment bulk density in the reservoir: 1.2 Trapping rate in the reservoir: 95 % Half storage of Saguling reservoir : Mcm 4.2. Reconstruction of the past sedimentation process of Saguling and current catchment condition Using the GIS model to compute the erosion rate for different management situations, the sedimentation process is reconstructed in order to estimate the present condition of the catchment. Sedimentation of the reservoir has accelerated over the last 10 years. It is suspected that land use change has contributed to this. The original and present storage characteristics of Saguling are summarized as follows Table 4.1. Characteristics Saguling reservoir storage Upstream Saguling catchment 2315 km2 Dead storage Volume 276 Mcm Level 623 m Full storage Volume 889 Mcm Level 643 m Dam construction Recently estimated (2004) sedimentation based on survey 150 Mcm Previously estimated reservoir half-life period (1/2 capacity sedimented) 189 years * construction was in the period ; it is assumed that the river channel was closed for construction and flows diverted (at a higher level) in Land-use changes in the basin have consisted of a substantial growth of the Bandung urban area and a de-forestation and/or degradation of forests, associated with a transition towards dry-land agriculture areas in the upper catchments. page 17

28 Using the GIS model the erosion potential was calculated for the following situations (see Table 4.2): Using the Modis mapping for 2001 and 2008 erosion estimates were made using the High, Low and Actual management conditions as defined in section In order to assess the effect of reforestation the potential erosion was calculated with the Modis 2008 mapping for the following cases; The Modis mapping offers a consistent picture on deforestation from 2001 to 2008, however the different types of agriculture are not well adapted to the Indonesian conditions; the Bakosurtanal (2009) and KLH map (based on corrected Landsat) has a better representation of the different crops; for comparison erosion computations have also been made with the Modis land-use mapping (illustrates the sensitivity of the erosion calculations with respect to land-use) The erosion estimates based on the Bakosurtanal land-use map are the lowest among the different land-use mappings which are considered. Table 4.2. Estimation of sediment generation for different land-use maps and management levels Management level Catchment erosion potential (M tons/year) low Actual high (1980) Modis land-use Modis land-use Modis (2008), with land >40 % turned into forest Modis (2008), with land >30 % turned into forest KLH map (Landsat, 2009) KLH map (Landsat, 2009) with land >30 % turned into forest Bakosurtanal (2009) Bakosurtanal (2009) with land>30% slope (25000 ha) turned into forest Original estimate (early 1980 s) Recent (2011) estimate BP-DAS: 112 Mton/year The following observations can be made: 1) A strong variation can be observed among the different erosion estimates using different landuse mapping. The different land-use maps have each strong and weak points. After checking/comparison of the maps it is believed that the Bakosurtanal (2009) map has by far the most detail; it is also the map which has been used as a basis for the current Java-Bali spatial plan. The erosion rate estimate based on the Bakosurtanal map will be adopted here in the further analyses. However the different results indicate that considerable uncertainty needs to be attached to this sediment estimate. 2) There are two processes which have caused the strong increase in sediment generation, viz a change in land-use which can be observed in the (Modis) mapping and a change in management, which is more difficult to observe, and for which we assume (guided by the simulation results) that the status has gradually gone from actual (reference situation considered by Hammer, 1980) to low at present 3) It is reasonable to consider a higher SDR for the basin, based on the effect of the extensive urbanization and canalization (a.o. Citarum river upstream of Bandung) which have substantially reduced sediment deposit areas in the downstream areas of the different sub-basins. The higher SDR strongly aggravates the sedimentation problem for Saguling. 4) In 2004 it was estimated from a survey that sediment deposition amounted to 150 Mm3; considering closure of the river channel for construction in 1982 this means an average sedimentation rate of 150/23=6.5 Mm3; the present rate of sedimentation will be higher as it suspected that the catchment has evolved from a reasonable condition (actual condition estimated by Hamer) in the early 1980 s to the present degraded condition; below an estimation is made of the current sedimentation rate based on a gradual increase of the sedimentation rate. page 18

29 5) Assuming that management of the catchment has shifted gradually Figure 4.1. Reconstructed sedimentation process Saguling from the situation in the early 1980 s to a present low management condition and considering that a strong deforestation has taken place from about 2000 (about half of the sediment load is caused by deforestation, see further) from 2000 on a rate of increase in sedimentation rate double that of the previous period ( ) can be reasonably assumed. Figure 4.1 then presents a reconstruction of the sedimentation process in Saguling for the period The estimated sediment rate in 2004 is then estimated at 12.1 Mm3 or 13.9 Mton/year. 6) Considering the above, the SDR for the Upper Citarum basin is estimated at 13.9/48.3=0.28 (28%); this represents a strong increase from the SDR of 9.9 % estimated in the early 1980 s; as argued above the Bandung region has strongly changed. 7) For computation of an indicative remaining life time in subsequent section a low and high sediment erosion rate of 10 and 15 Mton/year will be used and an SDR of 28%. 8) In the above an average SDR for the upper Citarum region is considered; however the SDR will be different for the different sub-catchments. Sub-basins Cihaur and Ciminyak discharge directly into Saguling reservoir, and can be expected to have a higher SDR than the other sub-basins (less opportunity for detached sediments to deposit on relatively low sloped portions of the catchment); the other sub-basins discharge into the main Citarum river in the Bandung valley; the Citarum river further experiences considerable back-water effect from a rock outcrop just upstream of Saguling, which controls river levels; the upstream section acts then to some extend as a sediment trap (from observations on dredged values and sediment load over the last 10 years the trapping coefficient is estimated at 0.10). This back-water effect also strongly influences flooding of the Bandung urban area. Dredging of this river section (proposed for flood control, see 6Ci s component C) will also contribute to conservation of Saguling. Obviously the long-term sustainable solution is to reduce sediment generation in the catchments. The Cihaur and Ciminyak basins are relatively small therefore the average value of 28% will be used in further computations. In summary, based on the above mapping and erosion analysis, the following observations can be made from the reconstruction of Saguling sedimentation over the period : considering the measured sedimentation of Saguling and the erosion rate under low management (low management is considered to represent a maximum erosion), it can be concluded that the current status of catchment management is very low, and that the SDR has increased substantially; this is compounded by a considerable deforestation (36,000 ha), with obviously a marked influence on erosion; from the analyses, the high sediment deposition in the period , expected to have continued to the present day, can be explained by a combination of: strong reduction in forested area; low catchment management (evolved from an earlier medium actual 1980 situation), and strong increase in SDR. page 19

30 4.3. Projection of future sedimentation with current trend Based on the above analyses the remaining time to fill the dead storage and remaining half life time for Saguling can be estimated as follows With a continuation of the current situation; remaining storage until dead storage filled = =126 Mcm yearly sediment inflow min= 10 Mton/year max= 15 Mton/year average SDR is = 0.28 remaining time to fill dead storage = min: 126/(15*1.1*0.95/1.2)= 9 years (from 2004) or 3 years remaining max: 126/(10*1.1*0.95/1.2)= 14 years ( ) or 6 years ( ) remaining storage until half- life storage = =293.5 Mcm remaining half- life time computation similar to the above indicates a remaining half life time varying between 16 and 27 years It can be concluded that an urgent and extensive catchment rehabilitation program is necessary to conserve the functions of Saguling reservoir for the longer term. page 20

31 FRESH_WATER POND SAND BAR ROCKS UNUSED_GRASS BUILT_UP DRY_FIELDS PLANTATION BUSH _SHR SAWAH_RAIN SAWAH_IRRI FOREST REFORESTRATION Appendix 3 - Upper Citarum Erosion and Sedimentation 5. IDENTIFICATION OF MEASURES TO MINIMIZE EROSION 5.1. Target for reducing erosion Interventions required to improve the current situation depend on the target which is set for the future sedimentation of Saguling. It is reasonable to re-establish as much as possible the original sedimentation condition; this original condition resulted in an accepted half-life time of 189 years. Taking into account an increased SDR (caused by strong changes in drainage in the basin) this means that the catchment will need to be upgraded to a higher management level than in the early 1980 s to get to the same sedimentation as adopted in the original planning for Saguling reservoir. The erosion estimates in Table 2.9 indicate that a high level of management and a substantial reforestation (land with slope >30%) can result in a sediment input of 6.07*0.28=1.7 Mton/year; which is already better than the original estimate of 2.7 Mton/year. Table 5.1 indicates the change in land-uses for the different sub-basins associated with the reforestation target. The slope >30% reforestation target amounts to a re-forestation of 25,000 ha; the largest transitions to re-forestation come from dry fields, plantations, and bush/scrub. This re-forestation target may seem large but should be compared to the much larger deforestation in the period (36,000 ha according to the Modis mapping). Table 5.1. Land-use in the different sub-basins Bakosurtanal (2009) land-use (reforestation >30%) Land use types Das name Citarik ,595 3, ,079 10,169 2,591 2,266 Cikapundung ,834 14,720 6,414 3, ,921 3,196 2,517 Cihaur ,775 3,272 1, ,311 4, Ciminyak ,851 2,622 5,231 1,454 7,077 2, ,936 Citarum hulu ,298 5,089 2,949 2, ,495 5,868 4,742 Cisankuy ,006 3,901 7,686 1,295 1,910 4,373 6,946 2,159 Ciwidey ,234 2,254 5,310 1,892 2,820 3,473 5,423 3,461 Cikeruh ,326 2,870 3, ,805 4,836 1,295 2,017 Total ,956 37,804 30,287 30,314 9,035 17,006 46,515 25,988 25,032 Bakosurtanal (2009) Total ,068 38,307 37,592 38,856 14,705 18,263 48,127 25,988 0 Difference ,305-8,543-5,670-1,257-1, ,032 It can be mentioned that implementing a high level of management for dry land agricultural areas has about the same effect for sediment as transformation into (production) forest. However for the sensitive higher slopes, forestation will be a much more (long term) robust solution ; it is observed that establishing a high management for the dry land (usually one crop during rainy season) agriculture in the higher sloped regions will be considerably difficult. A typical cultivation pattern for dry-land agriculture in those regions is cultivation during part of the year (when water is sufficiently available) and neglect during the rest of the year; forest provides then a more continuous ground cover throughout the year It is observed that land-use in current conservation areas deviates considerably from the original conception of the conservation areas, which was primarily to preserve forests which were there some time ago. page 21

32 FRESH_WATER SAND BAR ROCKS UNUSED_GRASS BUILT_UP DRY_FIELDS PLANTATION BUSH _SHR SAWAH_RAIN SAWAH_IRRI FOREST TOTAL Appendix 3 - Upper Citarum Erosion and Sedimentation In Section 5.2 below, an inventory is made of the current land-use in the conservation areas which shows a low percentage of remaining forest. Subsequently in Section 5.3 it is proposed to have a combined rehabilitation (forestry and agriculture) to manage the higher sloped areas. Section 5.4 proposes to include bush/scrub areas in conservation zoning. Section 5.5 summarizes the proposed catchment rehabilitation program. The same information forms the basis for a proposed zoning for the catchment which should secure a sustainable catchment for the long term future Current land-use in conservation areas Current land-use in conservation areas is estimated from an overlay of the Bakosurtanal ( 2009) land-use map and the harmonized spatial planning map. Land-use and conservation areas are presented on the map in Figure 5.1. Quantities for different land-use types are presented in Table 5.2. The following observations can be made: total area in the conservation zones in the Upper Citarum basin is 74,780 ha; a quite common thought on conservation areas is that they are mostly forested and thus wellprotected; from the land-use inventory in conservation areas this appears not the case, only 35 % is forested ; generally, forested - and sawah areas can be considered well protected (50%) ; this means that a considerable task remains to sufficiently protect the other types of land-uses To obtain a sufficient reduction in sediment load it is proposed (see further Section 6) to implement a.o. a reforestation for the areas with a slope >30%, because such areas are very sensitive and otherwise difficult to protect; it is further remarked that over the last decade a much larger amount of forest has disappeared. Increasing forested area also contributes to the spatial planning target for healthy watersheds of a minimum of 30% forest (actual situation for below this target). This reforestation considers also the areas in the spatial planning conservation zones, viz those with slope >30%. However the non-forested and non-sawah area in conservation zones (35,000 ha) is considerably larger than the proposed re-forestation (25,000 ha). Thus more reforestation may be in order to realize the objective(s) of conservation in the specified spatial planning conservation areas. This should be based on a (detailed) assessment of the conservation requirements in those areas. Table 5.2: Land-use in spatial planning conservation areas Land use types ha ,887 10,126 13,235 8,530 4,932 5,625 24,543 70,781 forest in conservation areas = 24,543 (35%) forest + sawah in conservation areas = 35,100 (50%) page 22

33 Figure 5.1. Slope classes for Upper Citarum basin 5.3. Protection of land with slope >30% It follows from the inventory of land-use in conservation areas that the nature of those areas has changed. Originally most of the conservation areas were conceived for protection of forests. Growing pressure on land is the likely cause for encroachment on those areas. The driving force for this appears to be that farmers on average cultivate a relatively small plot of land (insufficient to sustain a family), and seek to increase their land to obtain a minimum level of income. Figure 13 illustrates the population densities (desa level) for 2000 and 2008 (from PODES). The densities differ only slightly. page 23

34 Figure 5.2. Population density in 2000 and 2008 (desa) In view of the increasing share of agricultural land in sensitive areas, it becomes clear that management for those areas should involve forestry and agriculture. Some impressions for dry land agriculture from the Upper Citarum catchment are presented in Figure 5.3 (plenty of bare soil, no contouring/terracing) and 5.4 (well-managed slopes). page 24

35 Figure 5.3. Impressions from dry land agriculture with plenty of bare soil Figure 5.4. Impression of well managed dry land agricultural activity (site in Cisangkuy sub-basin) page 25

36

37 5.4. Upgrading of bush/scrub areas It is observed that the distinction in the mapping between the land-uses bush/scrub and forest is not so clear. Also the bush/scrub areas are found located adjacent to forest lands and/or conservation areas. The bush/scrub areas do not form a priority for rehabilitation of the catchment in order to reduce the sediment load. It is however prudent to protect them in the future. They will be included in the protection zoning in Section Summary of proposed catchment rehabilitation program Using the above info on re-forestation and considering a high management for the other land-uses in the basin (information in the tables of section 4.2), the watershed rehabilitation program can be described as follows: 1) on slopes >30% : combination of as much as possible re-forestation (preferred rehabilitation) and high management for remaining dry land agricultural areas (Figure 20 indicates these areas, involving an estimated total of 25,000 ha) 2) High management for non-irrigated agricultural areas, involving the following a. Surface mulch t/ha/year, imported if necessary. Application of mineral fertilizers, combined with manure and/or composts. Inter-cropping, high intensity, incorporating perennials. Legumes in rotation 1 year in 4. Maintenance ground cover 60-80%. High biomass production per area. High crop diversity. Intensive nutrient circulation. b. < 5% slope: high standard permanent contour grass strips well designed and maintained or: fully designed graded earthworks, or banks, with designed water disposal facility; > 5% slope: moderate standard bench terrace (i.e. not graded and without designed water disposal system, but risers stabilized grass or rocks. 3) High management for estates and plantations, involving the following a. < 5% slope: high standard permanent contour grass strips well designed and maintained or: fully designed graded earthworks, or banks, with designed water disposal facility; > 5% slope: moderate standard bench terrace (i.e. not graded and without designed water disposal system, but risers stabilized grass or rocks. b. Estate crops: high density permanent ground cover. Estate crops planted on contour where slopes exceed 10%. page 26

38 6. IMPACT OF IDENTIFIED MEASURES 6.1. Ranking of the effectiveness of erosion rehabilitation measures Identification of the larger sources of sediment and ranking of the effectiveness of the interventions is useful to guide the implementation of the catchment rehabilitation program. Table 6.1. Estimated erosion (Mton/year and ton/year/ha)) of the 8 sub-catchments Area Sediment yield low management DAS Name (ha) (Mton/year) Per ha (ton/year/ha) Citarik 25, Cikapundung 39, Cihaur 15, Ciminyak 31, Citarum hulu 37, Cisankuy 30, Ciwidey 26, Cikeruh 20, TOTAL 226, Table 6.1 presents the sediment generated in the different sub-catchments ; it can be observed that sub-basins Citarum Hulu and Cikapundung contribute the most in terms of total sediment load ; in terms of average intensity in sediment contribution per ha of catchment, the sub-catchments in the eastern part of the basin again contribute the most. A further differentiation according to land-use is made below. The effectiveness of measures can be based on the reduction in sediment generation, per unit area (ha), on the catchment areas due to the intervention (from low to high management). The unit efficiency for the re-forestation measure can be derived from the analysis results in Table 2.5. The simulated sediment loads (Bakosurtanal 2009 map) for reforestation >30% indicate a total reduction from 48.3 to 27.4 or 20.9 Mton/year; this means a reduction of 20.9/25032 = 835 ton/ha ; this means a reduction of sediment contribution to Saguling of 835*0.28=234 ton/ha/year. The efficiency of the other measures (resulting from a transition from low to high management) for the different land-uses is presented in Table 6.2. A wide range (0 to 246 ton/ha/year) of efficiencies can be observed. Improvement of dry land agriculture and plantations score the highest; other land uses appear rather insignificant. The (average) efficiency of reforestation (234 ton/ha/year) is higher than most of the improvements to dry agriculture. The annual sedimentation of Saguling under current catchment condition and run-off situation (SDR) is estimated at 13.9 Mton/year. The objective of the proposed catchment rehabilitation program (Section 5.1) is to reduce this to 6.07 * 0.28 = 1.7 Mton/year. This reduction should be realized most efficiently by tackling the areas with the highest unit potential for improvement and with substantial areas to realize sufficient reduction. Table 6.3 presents the contribution of each land-use type in the different sub-basins (unit reduction multiplied by area of the particular land-use in the particular sub-basin). From inspection of the areas with most potential for improvement (Table 5.1) and the total potential contribution (Table 5.2), a number of combinations of areas with particular sub-basin and particular land use are selected (shaded) which, together with the reduction realized by reforestation, can materialize the required reduction ( =12.2 Mton/year). page 27

39 FRESH_WATER POND SAND BAR ROCKS UNUSED_GRASS BUILT_UP DRY_FIELDS PLANTATION BUSH _SHR SAWAH_RAIN SAWAH_IRRI FOREST FRESH_WATER POND SAND BAR ROCKS UNUSED_GRASS BUILT_UP DRY_FIELDS PLANTATION BUSH _SHR SAWAH_RAIN SAWAH_IRRI FOREST Appendix 3 - Upper Citarum Erosion and Sedimentation Table 6.4 presents the set of most efficient/promising measures to establish the target reduction; this consists of the proposed re-forestation for slope > 30%, which contributes about half of the target reduction, and 10 combinations of land-use and sub-basin areas. Table 6.2. Efficiency of sediment reduction measures for different land-uses in different sub-basins Efficiency of reduction to Saguling sedimentation (ton/ha/year) due to improved management DAS name Citarik Cikapundung Cihaur Ciminyak Citarum hulu Cisankuy Ciwidey Cikeruh Table 6.3. Potential sediment reduction for different land-uses in different sub-basins Reduction to Saguling sedimentation (ton/year) due to improved management DAS name Citarik , , ,152 13,054 2,287 Cikapundung , ,135, , ,532 3,649 3,175 Cihaur , , , , Ciminyak , , ,789 2, Citarum hulu , ,400, , ,762 39,044 10,631 Cisankuy , , , ,639 3,501 8,156 Ciwidey , , ,805 5,944 3,753 Cikeruh , , , ,674 2,418 2,008 Table 6.4. Best measures to realize the target reduction of sediment input to Saguling Rehabilitation measures Area Efficiency Reduction (ha) (ton/ha/year) (Mton/year) Land-use sub-basin Re-forestation >30% All sub-basins Improved management Plantation Citarik Plantation Cikapundung Dry land Citarum hulu Dry land Citarik Dry land Cikapundung Plantation Citarum hulu Plantation Cihaur Dry land Cihaur Plantation Cimunyak Plantation Cisangkuy Total The following can be concluded from the above analysis - Re-forestation spread over all of the sub-basins accounts for slightly less than half (5.2 Mton/year) of the target reduction; the other part (7 Mton/year) can be realized through improved management for dry land (3.3) and plantations (3.7) concentrated in 6 of the subbasins. - The total area to be improved is extensive : 69,310 ha ; this is about a third of the total upper Citarum basin (226,517 ha). - A less ambitious rehabilitation target could be to ignore component 7, 8, 9 and 10 (a reduction of 15,673 ha and thus resulting in an alternative rehabilitation of a fourth of the basin); this, according to the analysis above, would result in a reduction of only 10.4 Mton/year and thus result in a sediment inflow in Saguling of =3.5 Mton/year compared to 2.7 of the initial estimation for Saguling. The remaining time for filling dead storage and half storage life-time are presented for both cases in next section. page 28

40 6.2. Projection of future sedimentation based on the proposed catchment conservation program Below a projection is made of future sedimentation of Saguling based on implementation of the identified measures and considering the two alternative targets; a transition is assumed from the present to the target condition in 10 years: Sedimentation period : 6*48.3*0.28=81 Sedimentation in the transition period ( ): for target 1.7 Mton/year 10* (48.3* )*0.5*1.1*0.95/1.2 = 66.3 Mcm for target 3.3 Mton/year 10* (48.3* )*0.5*1.1*0.95/1.2 = 74.1 Mcm Remaining dead storage in 2011: =45 It follows that dead storage will become filled within the transition period Remaining half-life time: for target 1.7 Mton/year ( )/(1.7*1.1*0.95/1.2)= 99 years Remaining half-life time from now: 99+10=109 years for target 3.5 Mton/year ( )/(3.5*1.1*0.95/1.2)= 45 years Remaining half-life time from now: 45+10=55 years From the above it can be concluded that controlling sedimentation of Saguling, to maintain an acceptable future functioning, critically depends on a high standard of control as well as a speedy implementation (10 years is probably optimistic) Remark on the distribution of sediment in the reservoir: The reservoir has a very elongated shape which causes most sediment to settle in the upstream parts of the reservoir and leaving a deeper pool of water in front of the dam. It can be expected that, although the amount of sedimentation equals and exceeds the dead storage volume, there will a deeper pool of water in front of the dam for a considerable time to come. However the sediment content in the water will steadily increase, especially with large inflow, causing (corrosive) problems for the turbines. page 29

41 7. ASSESSMENT OF RUN-OFF SENSITIVITY AND RUNOFF PROTECTION 7.1. Runoff and land-use change Catchment degradation, in particular the loss of infiltration- and retention capacity, leads to a larger and faster surface runoff, increasing peak flows and reducing low flow in the dry period. This phenomenon occurs in rural as well as urbanized areas. In general runoff and its distribution will be influenced by a number of variables such as the magnitude of rainfall, land slope, land-use, and hydro-geology. The hydro-topography of the Upper Citarum basin has a pronounced shape as illustrated in Figure 7.1. This consists of an extensive plain with very low gradients and steep slopes on the side; reason why this region is commonly called the Bandung bathtub (Cekungan Bandung). Runoff and runoff related problems are obviously strongly different in these different parts. Flooding is caused in the bottom of the bathtub where runoff from upstream catchment and uncompensated urban runoff are confronted with limited drainage. River works to improve channel capacity and thus drainage capacity, have been carried out, however the effect has been counteracted by land consolidation and sedimentation of the river channel caused by a strong increase in sediment load over the last decade (reference: component C). In the series of parameters influencing run-off, land-use is the parameter which can be changed through an intervention in the catchment. Figure 7.1. Topographical profile of the Upper Citarum basin Quantitative information on the influence of land-use on runoff is very limited. The only available, empirically verified (for USA conditions), data on the relationship can be found in the SCS methodology (curve Nr). The SCS unit hydrograph approach uses physical parameters of the catchment and the curve Nr (representing the influence of land-use) to estimate a runoff hydrograph. In next section an approximate analysis of the runoff in the small and steep catchments in the Upper Citarum basin, is made using curve Nr and the SCS unit hydrograph method. page 30

42 7.2. SCS hydrographs Brief review of the method: The US Soil Conservation Service (SCS) dimensionless unit hydrograph procedure is one of the most well known methods for deriving synthetic unit hydrographs. References for this method can be found in most hydrology textbooks or handbooks. The dimensionless unit hydrograph used by the US SCS has been derived based on a large number of unit hydrographs from basins with varying characteristics. An empirically verified relationship was established between the ratios of q/qp (flow/peak flow per mm of excess rainfall) and t/tp (time/time to peak). Formulas have been derived to estimate qp and tp based on characteristics from the catchment, those are: t L L (min) *(2, * CN) ,104* CN * Y Where: t L = time lag (minutes) L = flow path (m) CN = SCS curve number Y = average basin slope (m/m) 0.7 The lag time is derived as a function of the basin length, slope and Curve Number (land-use). Then the time to peak (tp) and the peak flow follow from D t p t L (hours) 2 q A p Q t (m3/s) p With: q p = peak flow (m3/s) D = rainfall duration in the analysis (hr) t p = time to peak (hr) A = catchment area (km2) Q = excess rainfall (mm) Runoff hydrographs for a typical catchment in the upper parts of the Upper Citarum basin: Figure 7.2 illustrates the derivation of the SCS hydrograph for a typical sub-cathment in the steeper sections (average slope >20%) of the Upper Citarum basin. Typical characteristics Watershed area: 50 km2 Flow distance : 10 km Average slope : 20% Estimated curve Nr (present uncontrolled situation/after reforestation and settlement control) : 75/65 Rainfall storm event considered in the analysis: 10 mm during 1 hour The hydrographs in Figure 7.2 illustrate a fast runoff and a marked influence of land-use (curve numbers), viz a 30 % reduction in peak flow and a delayed peak (from 1.8 to 2.2 hours). page 31

43 Figure 7.2. Runoff pattern (SCS hydrographs) for typical watershed for different land-use (curve numbers) 7.3. Runoff protection The hydrograph analysis illustrates the very quick response of the relatively small/short catchments with a high slope; it also illustrates the effect of re-forestation: a substantial reduction of the peak flow A re-forestation for areas with slope > 30% is proposed for catchment protection, this will also contribute substantially to runoff protection. A further protection of the catchment below slope 30% is proposed as follows: - between 30 and 15 % : restriction on further settlement - below 15% : settlement allowed if the increased runoff is compensated (ΔQ=0 policy) page 32

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45 8. PROPOSED ZONING FOR EROSION- AND RUNOFF PROTECTION 8.1. Introduction In previous sections analyses were made of the sensitivity of the catchment for erosion and runoff, leading to rehabilitation measures to strongly reduce the sediment load on Saguling as well as reduce the sedimentation of the main Citarum river channel in the Bandung valley, and reduce flood peaks from the upstream parts of the sub-catchments. For the longer term, spatial zoning should be put in place in order to safeguard and maintain catchment quality after rehabilitation. Such zoning is derived/proposed below, the sensitivity of catchment areas for erosion and runoff form again the main input for such zoning Setting for water resource zoning Inventory of water zoning requirements Water resources put a considerable number of requirements on spatial development, ranging from reservations for future infrastructure facilities to conditions on spatial activities to facilitate a proper functioning of water resources systems. The following types of zoning can be differentiated: 1) Space required for WR infrastructure (rivers, canals, reservoirs, area for temporary storage) 2) Spatial requirements associated with vulnerability for erosion 3) Spatial requirements related to runoff protection 4) Spatial reservations required for food crop production (UU41/2009) 5) Spatial specifications for flood prone areas (flood risk, reduction of damage) 6) Other natural disaster prone areas (land slides, earthquake, tsunami) The present report 2 addresses elements 2) and 3) from this list Objectives for water zoning Excessive erosion and - runoff have strong negative consequences; the objective of zoning is to reduce these consequences to a minimum. The following objectives can be differentiated 1) reduction of erosion: 2) runoff reduction (in particular peak flow) 3) enhanced production 4) contribution to the minimum 30% forest objective for healthy watersheds Spatial planning process relationship with water resources Figure 18 presents a sketch of different steps in water resources and spatial planning, progressing from a phase of policy/strategy formulation towards a detailed planning for implementation. Of particular relevance is here the specification of requirements from the WR sector. Specification of such requirements are made on the basis of an analysis of the functioning of water systems, such analysis is typically part of a river basin planning study. Two types of information emerge from the analysis of water systems, viz 1) which criteria should be applied to the protection of water systems in the spatial context, and 2) establishment of the spatial requirements (which interventions where). 2 In the 6Ci s project two GIS based models have been developed to address these two zoning components, those are: modeling of the USLE method including the effect of catchment management measures (see Sections 1 and 2 of this report), and a peak runoff zoning model indicating the catchment area contributing most to flood peaks (methodology presented in an annex to the B2 report) page 33

46 Figure 8.1. Water zoning in spatial planning The criteria are similar in nature to other areas of protection such as safety from floods, or other natural hazards. The criteria basically result from an assessment of the magnitude of impacts and a cost-benefit analysis for protection. The criteria on spatial requirements for WR are added to the set of zoning requirements in the spatial planning policy phase. The specific spatial requirements for the water systems should be incorporated into the detailed spatial planning, down to the 1:5000 and 1:1000 level for implementation of regulations and permits for spatial management Land-use classification in spatial planning and relationship to water zoning A total of 19 land-uses (of which some are further detailed) are differentiated in the detailed spatial plans. Table 18 provides an overview. A main classification can be made according to conservation area (Kawasan Lindung) and production area (Kawasan Budidaya). Some of the major land-use types under each category relevant to water zoning are Kawasan Lindung (Conservation area): comprising forest and public green space Kawasan Budidaya (Production area) o Kawasan Budidaya Berfungsi Lindung (production areas with a conservation function) Hutan produksi (production forest) Perkebunan (gardens) o Kawasan Budidaya Pertanian (agricultural production area) o Kawasan Budidaya Non-pertanian (non-agricultural area With respect to water, the interest is in managing the erosion, infiltration and retention characteristics of the catchment, based in particular on the physical characteristics (slope, soil, rainfall intensity) of different areas in the catchment. For these physical processes land-use is important in terms of its cover of the soil and obstruction to runoff. Good management for the different land-uses can substantially improve erosion, infiltration and retention. Depending on the characteristics of the location from the water point of view, conditions may be imposed (management) on the particular land-use in order to create favorable conditions for the water systems. For very sensitive areas certain land-uses (or expansion of those) may be even prohibited (for example further settlement in areas which strongly contribute to flood waves). In the water zoning analysis first sensitive zones are identified based on the physical attributes of the areas and then pose conditions on the type of land-uses which can be allowed, or allowed under specified management conditions. For example dry-land agriculture on steeper slopes is particularly vulnerable to erosion and fast runoff from bare soils, a condition for maintaining existing or allowing further dry-land agriculture is such places is to impose a regulation stipulating a requirement of high management (permanent ground coverage, contouring/terracing, slope protection, gully plugging, ). page 34

47 HUT, PU, DAGRI, LH, ABRI HUT, TAN, DAGRI, PT BUMN-HL1 KAWASAN BUDIDAYA HUT (BBKSDA), DAGRI, LH PU, DAGRI, HUT, LH HUT (BBKSDA), DAGRI, LH KAWASAN LINDUNG HUT (Kab/Kot), PU, DAGRI, LH HUT (BBKSDA, Perhutani), DAGRI, LH Appendix 3 - Upper Citarum Erosion and Sedimentation Table 8.1. Classification of zoning in the New Spatial Law (UU Nr 26/2007 Kawasan Institusi (institution) (zone) HUT (Perhutani) ESDM, DAGRI, HUT Deskripsi Kawasan (area description) (1) Kawasan Perlindungan bagi Kawasan Bawahannya (Protection zone for protecting the downstream part) (2) Kawasan Perlindungan Setempat (Locally protected zone) (3) Kawasan Suaka Alam dan Cagar Budaya (Nature and Heritage Conservation) (4) Kawasan Bencana Alam (Nature distaster area) (5) Kawasan Lindung Lainnya (other protected zone) (1) Hutan Produksi (production forest) (2) Hutan Rakyat (people forest) Jenis Kawasan (a) Kws Hutan Lindung (protected forest) (b) Kws Bergambut (peat land) (c) Kws Resapan Air (recharge Area) (a) Sempadan Pantai (coastal border) (b) Sempadan Sungai (river border) (spesific zone) (c) Sempadan Waduk dan Situ (reservoir and lake border) (d) Sempadan Mata Air (spring border) (a) Kws Suaka Alam (nature conservation) (b) Kws Suaka Alam Laut dan Perairan Lainnya (c) Kws Pantai berhutan Bakau (mangrove in coastal) (d) Taman Nasional (national park) (e) Taman Hutan Raya (TAHURA) (f) Taman Wisata Alam (nature recreation park) (g) Cagar Alam (nature conservation) (h) Suaka Margasatwa (wild fauna conservation) (i) Kws Cagar Budaya dan Ilmu Pengetahuan (heritage and science) (a) Kws Rawan Letusan Gunung Berapi (vulcano disaster) (b) Kws Rawan Gempa Bumi (earth quake disaster) (c) Kws Rawan Tanah Longsor (landslide disaster) (d) Kws Rawan Gelombang Pasang (tsunami disaster) (e) Kws Rawan Banjir (flood disaster) (a) Kws Taman Buru (hunting recreation park) (b) Kws Cagar Biosfir (biosphere conservation) (c) Kws Perlindungan Plasma Nutfah (bio-diversity/genetic conservation) (d) Kws Pengungsian Satwa (wild animal evacuation) (e) Terumbu karang (coastal reef) (3) Pertanian, Perkebunan dan Peternakan (agriculture, plantation, animal husbandry) (4) Perikanan (fresh and saline water fishery ) (5) Pertambangan (mining) Hutan/ Non- Hutan (in or outside forest) H H/NH H/NH NH NH NH H/NH H/NH H/NH H/NH H/NH H/NH H/NH H H/NH H/NH H/NH H/NH H/NH H/NH H/NH H/NH H/NH H/NH H/NH H/NH H NH NH NH H/NH Tindakan Konservasi (conservation measures) Reboisasi (reforestation), Tanaman kehutanan (forest plant) Penghijauan, Agro-Forestry Agro-Forestry, Terasering (teraccering), Rorak (Parit Buntu), Strip Rumput (stripped grass), Mulsa vertikal (slot mulch), Tanaman penutup tanah (cover crops), Ternak (animal husbandry), Perikanan (fishery), Bio-Gas, Kompos (composting), Dam Penahan, Dam Pengendali, Pengendali erosi jurang (gully plug) Penghijauan dan Rehabilitasi Bekas Tambang (exmining regreening and rehabilitation), Kompos (composting) (6) Pemukiman (settlement) (7) Industri (industry) NH Penghijauan (regreening), Hutan/Taman-Kota (city park/forest), Turus Jalan (greening along highway), Sumur Resapan (recharging well or infiltration (8) Pariwisata (tourist resort) (9) Tempat Ibadah (religion) NH NH gallery), Bio-pori (bio-pore), Bio-Gas, Pengolahan Sampah rumah tangga (domestic waste processing/recycling), Kompos (composting), (10) Pendidikan (education) (11) Pertahanan Keamanan (defence and security) NH NH Pengolahan Limbah Industri (industrial waste processing) HUT Kementrian Kehutanan (Foresrty Department) LH Kementrian Lingkungan Hidup (Ministery of Environment) PU Kementrian Pekerjaan Umum (Public Work Department) DAGRI Kementrian Dalam Negeri TAN Kementrian Pertanian (Agriculture Department) ESDM Reboisasi/Penghijauan, Pengkayaan (enrichment), Vegetasi Asli (native vegetation) atau Tambahan dan Permanen, Tanaman Bakau (mangrove) di pantai, Embung (small dam), Dam pengendali (check dam), Dam penahan (sediment retention dam), Pengendali Tebing Sungai dengan tanaman bambu (bamboo) dan rumput gajah (river bank erosion control), Stabilitas Lereng (slope stability) Reboisasi/Penghijauan (reforestation/regreening), Pengkayaan (enrichment), Vegetasi asli (native vegetation), Permanen. Penanaman dan pemeliharaan terumbu karang (coastal reef plantation and maintenance) Kementrian Energi dan Sumberdaya Mineral (Department of Energy and Mineral Resources) BBKSDA Balai Besar Konservasi Sumber Daya Alam (Nature Conservation council) Perhutani Perusahaan Kehutanan Indonesia ABRI Angkatan Bersenjata Republik Indonesia PT BUMN HL PT Bakti Usaha Menanam Nusantara Hijau Lestari-1 page 35

48 To analyze the influence of land-use on water systems it is sufficient to consider a few major classes of land-use, such as for example represented in the Bakosurtanal 1:25,000 land-use map; this map does not distinguish the wider set (19) of socio economic functions associated with the use of land such as in spatial planning; the origin of information of the Bakosurtanal land-use map is an optical sensing (satellite) which does only allow to characterize the physical occupation of the land-use on the land. This is however sufficient to establish the influence on erosion and runoff. After identifying the sensitive zone the further details of the spatial plan should be filled in with the local (Kabupaten) plans. For example the bare soil sensitive areas can be identified based on the physical characteristics of the area and its function in the water systems; this can lead to the following detailing at the local level and the associated management action: for agricultural areas: a high management should be implemented for build-up areas in this zone: implementation of infiltration measures such as infiltration pits for runoff from rooftops, and prohibition of drainage of local depression areas which act as retention during high rainfall 8.3. Proposed water zoning related to erosion and runoff protection Considering, - the objectives for zoning, - the analysis of sensitivities for erosion and runoff and relationships with land-use in the previous sections, and - the relevant (major) land categories in the section above, the following zoning to protect water related interests is proposed: 1) An expanded conservation area (Kawasan Lindung) comprising the following: a. The current conservation area b. Re-forestation in areas with slope > 30% c. Protection of bush/scrub areas 2) Protection of dry-land agriculture and improvement of infiltration for a bare soil sensitive zone: 3) Special protection zone for flood peak runoff Ad 1): the measures to be taken for this expanded conservation zone include - Where possible (in particular on state owned lands) re-forestation, this includes reforestation of the recently deforested areas in the current conservation areas; - protection of current bush/scrub areas (usually state owned) against possible further degrading; upgrading of those areas to (production) forest in the future; they are not a priority for rehabilitation because they are not a serious problem for erosion and runoff. - Further settlement should be prevented Ad 2): measures to be taken for this zone: - High management for agricultural areas with main focus on permanent ground cover, mixed cropping, terracing, protection of slopes, - Measures to increase infiltration and reduce surface runoff in build-up areas (infiltration pits, retention ponds) Ad 3): special protection of particular parts of the catchment based on the hydrologic/hydraulic behavior of the catchment ; - re-forestation where possible, - high management for agricultural activities, - natural depression/retention areas need to preserved; creation of extra retention (this is the zone where retention has a maximum effect) ; - further settlement should be prevented unless in areas with a slope <15 % and with obligatory implementation of the ΔQ=0 policy. The proposed zones are elaborated for the Upper Citarum basin in next section page 36

49 8.4. Elaboration of the proposed zones for the Upper Citarum Conservation for highly sensitive areas Areas with a very high erosion sensitivity are difficult to control and generally located on high slopes at higher altitudes. A general approach is to conserve such areas with a forest cover and further allocate an ecological function (healthy watershed) to those areas. The re-forestation- and protection of dry agricultural areas, proposed in next sections already cover the very high erosion sensitivity areas by either considering re-forestation or high management. Figure 8.2 illustrates the effect of high management on the erosion sensitivity. Figure 8.2. Erosion sensitivity for low (map above)and high management (map below) page 37

50 Re-forestation In Section 5 re-forestation (production forest) is characterized as a highly efficient means for reducing the sediment load on Saguling. As indicated in Section 3 such re-forestation represents only a partly recovery of forest which has been lost over the last decade. Figure 8.3 presents the proposed reforestation areas. Figure 8.3. Areas (slope >30%) considered for re-forestation As elaborated in Section 5, due to increasing pressure on land in recent years, encroachment has taken place on previously forested areas with strong consequences for erosion and runoff. For a long term sustainable situation priority should be given to re-forestation of steeper sloped areas (>30%) which is most effective and desirable. Depending on the local situation (o.a. ownership) this can be combined with high management on patches of dry-land agriculture in those steep areas. Re-forestation will also have a considerable beneficial effect on runoff as elaborated in Section 7. In view of the importance of this forest zone, both for erosion and runoff, this zone should be strictly managed and this should be indicated in the spatial plan as such. In this zone further expansion of dry agriculture should not be allowed and a special effort should be put into reclaiming previous encroachment on the forested area and enforce a high management for the remaining agricultural areas Upgrading of bush/scrub areas expanded conservation zone It is observed that in land-use mapping the land-uses forest and bush/scrub are difficult to distinguish; also the bush/scrub areas are found adjacent to forest lands and current conservation areas. Most likely they were forest before and have degraded. Although they do not form a priority for rehabilitation of the catchment (see Section 6) aimed at reducing the sediment load, it is probably prudent to consider them for protection in the future and include them in the zoning. For zoning it is then proposed to add them to the re-forestation zone. page 38

51 As proposed in Section 8.3 an expanded conservation zone is considered which includes the current conservation zone, the proposed re-forestation and the bush/scrub areas. Such expanded conservation zone is indicated in Figure Protection of bare soil Low management of dry land agriculture has been indicated (Section 6) as a major source of sediment load on Saguling; some parts of the basin (based on their physical characteristics) make an exceptionally high contribution to the sediment load. A high proportion of bare soil, characteristic of low management, has also strong effects on runoff. A zone has been defined with a bare soil erosion potential of >500 ton/ha/year (bare soil erodibility is on average about 3 times as large as for other land-uses); establishing a high level of management for those areas will be important to bring the current sediment load under control and improve runoff. Figure 8.4 presents the combination of the proposed expanded conservation zone (dark green) and the dry land agricultural protection zone (light green). Maintaining a high level of management for those areas will be important for a long term sustainable situation. Such management should be secured by a zoning in the spatial plan. This consists of a delineation of the sensitive zones and specification of the regulation. Figure 8.4. Areas (slope >30%) considered for re-forestation page 39