Understanding intra catchment processes related to management of tropical headwater catchments

UNDERSTANDING INTRA-CATCHMENT PROCESSES RELATED TO MANAGEMENT OF TROPICAL HEADWATER CATCHMENTS BY JUNJIRO N. NEGISHI (M.Sc.) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF GEOGRAPHY NATIONAL UNIVERSITY OF SINGAPORE 2005 Acknowledgements I would like to sincerely and truly thank my primary supervisor Professor Roy C. Sidle for providing me a precious opportunity to conduct Ph.D. studies with him in the tropics, in particularly in the field of hydrogeomorphology. Without his frequent involvements in sometimes tedious fieldworks, inspiring, thoughtful, and constructive suggestions and comments, continuous support and encouragement, and patience, this dissertation would have never been put together in the present form. I also would like to express my sincere appreciation to Dr. Abdul Rahim Nik from Forest Research Institute Malaysia for supporting and allowing me to have an flexible access to the Bukit Tarek Experimental Watershed; also he helped me much in various logistical aspects including provision of some hydrological data and facilitation of equipment transportations between Singapore and Malaysia. Dr. Shoji Noguchi from Japan International Center for Agricultural Sciences provided invaluable help such as sharing his field laboratory and offering logistical help in the field, which were instrumental in continuation of this study. Associate Professor Robert Stanforth welcomingly and kindly arranged access without problems to the analytical equipments at the Department of Chemical and Biomolecular Engineering at NUS. My frequent visit and stay in the field site could not be more pleasant, relaxing, and exciting without the presence of my great neighbors in a small kampung of Kerling: the family of Mahmud Marzuki; I sincerely thank them all for taking care of the field station and myself largely by cleaning our field laboratory, providing various kinds of food and drinks (including amazingly addictive durians), and opportunity to join celebrative gatherings. Associate Professor Matthias Roth was very helpful and kind to me particularly by dealing with necessary paper works while I was away from Singapore to work closely with Professor Sidle in Japan. I not know how to thank Alan Ziegler for fueling my continuous motivation in field sciences and providing me valuable thoughts and insights related to this dissertation. Masanori Nunokawa, Shozo Sasaki, Takashi Gomi, Noriko Kodera, Peiwen Tham, Ruyan Siew, Josephene Then, and Mika Yamao provided me capable help in the field; their assistance was indispensable especially when working in a place far from home rather independently. My gratitude also must go to Professor Makoto Tani, Associate Professor Zulkifli Yusof, Associate Professor John S. Richardson, Associate Professor Hideaki Shibata, Takashi Gomi, and Shoji Yasushi for valuable and helpful suggestions and guidance when I was having hard time to get around some obstacles in pursuing Ph.D. program. Masahisa Nakamura, Yuko Nakamura, Rino Nakamura, Shogo Nakamura, Karin Laursen are all very much appreciated for their continuous support in various aspects during my academic journey so far. My parents Takeo Negishi, Yukiko Negishi, and brother Yoichiro Negishi have been always supportive and encouraging to me; their presence had meant so much to me throughout my academic training until today. Last but not least, Miho Negishi, Yutaka Negishi, and Suzu Negishi have been an fundamental and irreplaceable key ingredient in this great accomplishment and all the related dissemination made; thank you all for cheering up and supporting me all the way through. I Table of Contents ACKNOWLEDGEMENTS ··················································································· I TABLE OF CONTENTS ····················································································· II SUMMARY ································································································· VI LIST OF FIGURES ························································································· VII LIST OF TABLES ·························································································· XIII GLOSSARY ································································································ XV CHAPTER 1. INTRODUCTION ·········································································· 1.1. 1.2. 1.3. 1.4. BACKGROUND ·························································································· OBJECTIVES OF THE DISSERTATION ······························································ STUDY APPROACH ····················································································· OUTLINE OF THE DISSERTATION··································································· CHAPTER 2. SITE DESCRIPTIONS ··································································· 2.1. 2.2. STUDY SITE ····························································································10 MAJOR MONITORING LOCATIONS ·································································17 2.2.1 Sites within C1 ················································································17 2.2.2 Sites within C3 ················································································23 2.2.1.1 ZOBC1···························································································17 2.2.1.2 Floodplain and planer hillslope ·························································20 2.2.2.1 Experimental road section ································································23 2.2.2.2 Rainfall monitoring stations ·····························································28 CHAPTER 3. STORMFLOW GENERATION WITHIN C1 ZERO-ORDER BASIN ····· 30 3.1. 3.2. 3.3. CHAPTER ABSTRACT ·················································································31 CHAPTER INTRODUCTION ··········································································32 METHODOLOGY ·······················································································33 3.4. DATA ANALYSES ·······················································································40 3.5. RESULTS ································································································43 3.6. DISCUSSION ···························································································59 3.3.1 3.3.2 Hydrometric approaches····································································33 Hydrochemical approaches ································································38 3.4.1 3.4.2 3.4.3 ZOB flow separation ·········································································40 SOF estimation ················································································42 Pipe flow responses and contribution···················································43 3.5.1 3.5.2 3.5.3 3.5.4 3.5.5 3.5.6 ZOB flow responses ··········································································45 Contribution of SOF due to DPSA·······················································45 Pipe flow responses and contribution···················································47 Piezometric responses ·······································································55 Sporadic measurements of rainfall, runoff, and saturated soil water········55 Intensive event monitoring of rainfall, runoff, and saturated soil water····55 CHAPTER 4. INTRA-CATCHMENT HETEROGENEITY OF HYDROLOGICAL PROCESSES AND SOLUTE EXPORT WITHIN C1 ··············································· 66 4.1. 4.2. 4.3. CHAPTER ABSTRACT ·················································································67 CHAPTER INTRODUCTION ··········································································68 METHODOLOGY ·······················································································69 4.3.1 Hydrological monitoring ····································································69 II 4.3.2 4.3.3 Hydrochemical monitoring·································································73 Analytical approaches ·······································································77 4.4.1 4.4.2 4.4.3 Hydrological responses of floodplain, hillslope, and ZOBC1 ····················80 Variability of streamwater chemistry reflected in specific conductance·····87 Heterogeneity in solute concentration and export··································90 4.3.3.1 Stormflow separation ·······································································77 4.3.3.2 Characterizations of solutes from planar hillslope during storm events ···78 4.3.3.3 Statistical consideration ···································································79 4.4. RESULTS ································································································79 4.5. DISCUSSION ···························································································93 CHAPTER 5. ROAD INTERVENTION ON CATCHMENT PROCESSES WITHIN C3: SOURCE OF HORTONIAN OVERLAND RUNOFF··············································104 5.1. 5.2. 5.3. CHAPTER ABSTRACT ··············································································· 105 CHAPTER INTRODUCTION ········································································ 106 METHODOLOGY ····················································································· 107 5.4. ANALYTICAL APPROACHES ······································································· 113 5.5. RESULTS ······························································································ 119 5.6. DISCUSSION ························································································· 127 5.3.1 5.3.2 5.3.3 Hydrological Monitoring·································································· 107 Event-based Monitoring of Sediment and Specific Conductance ············ 110 Monitoring of water temperature, turbidity and specific conductance····· 112 5.4.1 outlet 5.4.2 5.4.3 Separation of event-based stormflow flux at the road section and catchment ···································································································· 113 Estimation of HOF on the road section ·············································· 113 Separation of HOF at the catchment outlet ········································ 117 5.5.1 5.5.2 5.5.3 5.5.4 Examples of road section response ···················································· 119 Examples of catchment outlet responses ············································ 121 Road HOF response and its contribution to catchment runoff ··············· 124 Estimation of contribution area of HOF ············································· 124 CHAPTER 6. PROCESSES RELATED TO INTERCEPTED SUBSURFACE FLOW (ISSF) WITHIN C3: HYDROLOGICAL RESPONSES AND ROAD EROSION ···········134 6.1. 6.2. 6.3. CHAPTER ABSTRACT ··············································································· 135 CHAPTER INTRODUCTION ········································································ 136 METHODOLOGY ····················································································· 137 6.3.1 6.3.2 6.3.3 6.3.4 Characterization of in-stream condition ············································· 138 Hydrological monitoring ·································································· 138 Event-based monitoring of sediment ················································· 140 Analytical approaches ····································································· 140 6.4.1 6.4.2 6.4.3 6.4.4 6.4.5 Catchment suspended sediment export·············································· 143 In-stream characteristics································································· 145 Relative contributions of HOF and ISSF to road runoff ························ 145 Characteristics of ISSFZOB and ISSFhillslope ········································· 151 Relative contributions of HOF and ISSF to road sediment export ·········· 151 6.5.1 6.5.2 Observation at catchment scale ························································ 156 Hydrologic control of ISSF ······························································· 158 6.3.4.1 Event-based separation of road-related HOF and ISSF ······················· 140 6.3.4.2 Estimation of sediment export························································· 142 6.3.4.3 Statistical analyses········································································ 143 6.4. RESULTS ······························································································ 143 6.5. DISCUSSION ························································································· 155 III 6.5.3 6.5.4 6.5.5 Geomorphic control of ISSF ····························································· 159 ISSF-driven sediment export···························································· 160 Occurrence of ISSF and road impacts ················································ 162 CHAPTER 7. DYNAMIC SOURCE AREAS OF SEDIMENT AND SOLUTE WITHIN C3 ································································································165 7.1. 7.2. 7.3. CHAPTER ABSTRACT ··············································································· 166 CHAPTER INTRODUCTION ········································································ 168 METHODOLOGY ····················································································· 169 7.4. RESULTS ······························································································ 176 7.5. DISCUSSION ························································································· 187 7.3.1 7.3.2 7.3.3 7.3.4 Hydrological monitoring and sporadic hydrochemical monitoring ·········· 169 Event-based monitoring of sediment and solute ·································· 172 Selected solutes examined ······························································· 172 Analytical approaches ····································································· 172 7.4.1 Sporadic characterization of stormflow components····························· 176 7.4.2 Typical characteristics of sediment and solute export from the experimental road section ······························································································· 176 7.4.3 Typical characteristics of sediment and solute export from the catchment outlet ···································································································· 180 7.4.4 Total export and contribution of HOF-induced sediment and solute export ·· ···································································································· 182 CHAPTER 8. ECOLOGICAL PROCESSES RELATED TO CATCHMENT RECOVERY OF C3 ································································································194 8.1. 8.2. 8.3. CHAPTER ABSTRACT ··············································································· 195 CHAPTER INTRODUCTION ········································································ 196 METHODOLOGY ····················································································· 197 8.4. ANALYSES ···························································································· 203 8.5. RESULTS ······························································································ 207 8.3.1 8.3.2 8.3.3 8.3.4 Precipitation and road runoff ··························································· 197 Interception loss and throughfall quality ··········································· 197 Sediment export ············································································· 201 Temperature ·················································································· 203 8.4.1 8.4.2 8.4.3 8.4.4 Road runoff separation ···································································· 203 Interception loss and element enrichment estimation ·························· 204 Sediment and air temperature data ·················································· 206 Further statistical considerations ····················································· 206 8.5.1 8.5.2 8.5.3 Road runoff estimation···································································· 207 Interception loss and element contents at road sites ···························· 208 Interception loss and element enrichment of fern cover and forest canopy ··· ···································································································· 211 Influences of fern cover on rainfall and elemental inputs on the road surface ···································································································· 211 Sediment export ············································································· 214 Air temperature ············································································· 214 8.5.4 8.5.5 8.5.6 8.6. DISCUSSION ························································································· 217 CHAPTER 9. CONCLUSIONS·········································································223 9.1. 9.2. CHAPTER INTRODUCTION ········································································ 224 SUB-OBJECTIVE 1: TO ELUCIDATE INTRA-CATCHMENT VARIABILITY RELATED TO STORMFLOW GENERATION AND SOLUTE EXPORT WITHIN A RELATIVELY UNDISTURBED IV TROPICAL HEADWATER CATCHMENT. ··································································· 224 9.3. SUB-OBJECTIVE 2: TO UNDERSTAND HOW LOGGING ROAD NETWORKS ALTER PROCESSES AND PATHWAYS RELATED TO STORMFLOW GENERATION AND EXPORT OF SEDIMENT AND SOLUTES WITHIN A SEVERELY DISTURBED TROPICAL HEADWATER CATCHMENT··································································································· 228 9.4. SUB-OBJECTIVE 3: TO DOCUMENT RECOVERY PROCESSES OF ROADS ASSOCIATED WITH VEGETATION REGROWTH AFTER CATCHMENT DISTURBANCE RELATED TO SEDIMENT, WATER, AND SOLUTE DYNAMIC ··········································································· 232 9.5. MANAGEMENT IMPLICATIONS··································································· 233 REFERENCES ·······························································································239 V Summary Various intra-catchment processes were studied in two neighboring tropical headwater catchments of Peninsular Malaysia: a relatively undisturbed catchment (C1, 33 ha) and a catchment severely disturbed by logging activities (C3, 14 ha). C1 remains undisturbed since selective harvesting in the 1960s whereas C3 was selectively harvested years ago with constructions of extensive road network. Hydrochemical monitoring of a zero-order basin (ZOB) within C1 indicated that subsurface flow accreted above the soil-saprolite interface provided a major stormflow component. Soil pipes at the channel head (i.e., profile at the basin outlet) contributed an approximately 50% of total ZOB flow during the study period, suggesting being as an important pathway for draining solute-rich stormflow to downstream systems In comparison with planer hillslope and riparian floodplain, ZOB was hydrologically the most dynamic and played a disproportionately important role in exporting solutes such as nitrate. The levels of selected solutes such as nitrate exported during events from a zero-order basin were higher compared with those from a planer hillslope, likely due to a greater contact of subsurface flow with shallow organic-rich soil horizons in the converging zero-order basin. Consequently, estimated export of selected solutes was 4- to 6-fold higher from a zero-order basin relative to a planer hillslope. Road surfaces in C3 altered catchment hydrology by extensively promoting overland flow. Contributing areas of HOF (Hortonian overland flow) to the outlet of C3 expanded from 0.1 to over 1.5 with increasing storm rainfall over a range from to 88 mm at least for events with wet antecedent condition. Such expansion of HOF contributing areas was partly attributed to variable connectivity between source areas (road surfaces) and stream channels related to event characteristics. In addition to generating HOF and associated surface erosion, road cuts intercepted subsurface flow (ISSF) during relatively large events, resulting in additional road surface erosion and bypassing of solute-rich flow downslope of the roads. Consequently, for the intensively monitored storms in which high ISSF inputs were observed, ISSF-related sediment accounted for 27% of the total sediment exported from the road section. Nearly all the sediment eroded from the road section was originated from the road prism (>90%). In contrast, source areas of solutes were highly variable; the major source of solutes was road surface for the events with road runoff dominated by HOF, whereas the majority of solute export from the road section (>60%) was accounted for by the inputs from upslope of the road prism when substantial ISSF drained from the cutslope. Absence of vegetation on the road surface likely caused continuous, excessive surface erosion. Growth of roadside fern (D. curranii) plays an important ecological role in road recovery through the following processes: (1) reduction of HOF (-4.8 mm); (2) reduction of sediment export rate (-84%); (3) enhanced fluxes of selected nutrients (K: +101%, Mg: +70%, Ca: +26%); and (4) suppression of maximum air temperature (-7 ºC). VI List of Figures Figure 2-1 Location of Bukit Tarek Experimental Watershed in Peninsular Malaysia 11 Figure 2-2 Topographic map of Bukit Tarek Experimental Catchments and 3. 12 Figure 2-3 View of a) skid trail and b) main logging road within C3 in October 2002 14 Figure 2-4 View of a) road cutslope and b) surface of main logging road; note that there is conspicuous soil saprolite interface at an approximate depth of m (shown by an arrow) (a) and exposed saprolite on the road surface (b) 15 Figure 2-5 Locations of monitoring sites within C1. .18 Figure 2-6 Details of zero-order basin (ZOBC1) within C1. Inset shows the cross-sectional view of the ZOBC1 channel head; inset illustrates the soil profile at the channel head with locations of soil pipes. 19 Figure 2-7 Details of floodplain and the foot of planar hillslope within C1. Note that dark gray area within the floodplain denotes a saturated soil surface; the extent of saturated surface area and subsurface water level for groundwater monitoring wells were both determined on December 2002. S-S interface refers to the soil-saprolite interface. 21 Figure 2-8 Location of monitoring sites within C3. .24 Figure 2-9 Details of the areas around the experimental road section. a) a view of ZOBC3; SB: slope boundary across which the road cut down to the saprolite layer; ZB: zero-order basin boundary, and b) a schematic diagram showing road runoff nodes, ZOBC3 outlet, and the directions of Hortonian road runoff; the shaded area on the road denotes noticeable rills where flow tended to concentrate; LB: logging road drainage boundary; A and B: gullies where road runoff drained to the downstream system. Note that the picture in panel a) was taken in January 2004 immediately after the catchment was clear-felled and burnt with little alteration of pre-disturbance surface topography .25 Figure 2-10 View of a) road surface with occurrence of Hortonian overland flow and b) road surface of the experimental road section with noticeable rills. .26 Figure 2-11 Locations of two rainfall monitoring sites within C3. Monitoring periods for stations A and B were 10 November 2002 - 22 November 2003, and 23 November 2003 23 November 2004, respectively .29 Figure 3-1 Instrumentations within the zero-order basin in C1 (ZOBC1). For the detailed information about the map, please refer to the section 2.2.1.1 .35 Figure 3-2 View of channel head areas of the zero-order basin within C1; a) ZOBC1 weir and soil profile, and b) soil pipes 2, 3, and on the soil profile. Details of the soil profile are provided in Figure 3-1 and text (see the section 2.2.1.1). 36 Figure 3-3 Schematic diagrams showing four cases of ZOB flow separation: (a) case 1, (b) case 2, (c) case 3, and (d) case 4. See the text for details about each of the cases. .41 Figure 3-4 Frequency distribution and runoff responses of storm events observed between November 2002 and November 2004. Open circles and bars denote storms with ARI7 < 30 mm; closed circles and bars corresponded to storms with ARI7 ≥ 30 mm. Numbered storms are those during which interception of subsurface flow was observed at the road runoff node; more detailed information on these events is shown in Table 3-2. Dotted lines indicate regression lines that significantly predicted runoff depth from incident precipitation; see the text for more details of hydrograph separation .44 Figure 3-5 a) precipitation, b) responses of total ZOB flow and combined pipe flow, c) responses of individual pipes, and d) the relative contribution of pipe flow during an event on 31 August 2004 (PRT=25.4 mm, ARI7=6.6 mm, Imax10=25.2 mm h-1). Note that the legend of Figure 3-5d corresponds to those of Figure 3-5c. 48 Figure 3-6 a) precipitation, b) responses of total ZOB flow and combined pipe flow, c) response of total head of Psat, d) responses of individual pipes, and e) the relative contribution of pipe flow during the event on July 2004 (PRT=76 mm, ARI7=0 mm, Imax10=104 mm h-1). Note that the legend of Figure 3-6e corresponds to those of Figure VII 3-6d. The inset in Figure 3-6d enlarged the initial flow response denoted by an arrow. 49 Figure 3-7 a) precipitation, b) responses of total ZOB flow and combined pipe flow, c) response of total head of Psat, d) responses of individual pipes, and e) the relative contribution of pipe flow during the event on Oct 2003 (PRT=86 mm, ARI7=32.3 mm, Imax10=110 mm h-1). Note that the legend of Figure 3-7e corresponds to those of Figure 3-7d. The inset in Figure 3-7d enlarged the initial flow response denoted by an arrow. 50 Figure 3-8 a) logarithmic models that relate total ZOB flow rate to flow rate of individual pipes, which were derived from monitoring of pipe flow rate during the study period; see Table 3-3 for the model details, and b) contribution of individual pipes against total ZOB flow rate. Note that x-axes on both panels and y-axis on panel a) are on logarithmic scales. .51 Figure 3-9 Event-based contributions of a) four pipes combined, b) pipe 1, c) pipe 2, d) pipe 3, and e) pipe 4. Note that relationships in panels a), b) and c) were polynomial models; relationships in panels d) and e) were exponential decay models. 54 Figure 3-10 A) responses of deep piezometers relative to total ZOB flow; dotted lines correspond to the depth of shallow piezometers (SP). B) responses of SP relative to deep piezometer (DP); dotted 1:1 lines predict the relationship between SP and DP when responses of SP is caused by rising of saturated zone detected by DP. 56 Figure 3-11 Silicon concentration and specific conductance of various sources measured in “non-event period” monitoring. P-1, P-2, P-3, and P-4 denote pipes 1, 2, 3, and 4, respectively. Numbers in brackets besides source ID denotes sample sizes. Letters above bars indicate the results of Tukey’s multiple comparison following one-way ANOVAs that were separately conducted for the two variables; data for specific sites accompanied with different letters were statistically different. .57 Figure 3-12 For three storms in November 2004, the following data are shown: a) precipitation, b) flow rate of the ZOB and pipe 1, c) flow rate of pipe 2, and BR, d) specific conductance, and e) silicon concentration from various sources: sources are zero-order basin (ZOB), soil pipes, and bedrock (BR). Note that data for the pipe is not shown because monitoring was terminated in May 2004. Missing flow response of pipe was caused by shortage of data storage in monitoring instruments. .58 Figure 4-1 Instrumentation within ZOBC1. 71 Figure 4-2 Instrumentation within the floodplain and near the foot of planar hillslope within C1. .72 Figure 4-3 Hydrological responses observed at the floodplain runoff weir for two events: a) total rainfall of 51 mm with ARI7 of mm; b) total rainfall of 78 mm with ARI7 of 130 mm. c) responses of overland flow caused by direct precipitation falling onto saturated floodplain against event-based precipitation; filled and open circles correspond to the events with ARI7 >30mm and 30 mm. Solid lines were fit using linear regression models. For ZOB, two different levels of antecedent moisture conditions were plotted separately. .95 Figure 5-1 The location of Bukit Tarek Experimental Watershed (BTEW) and experimental road section, zero-order basins, and catchment outlets; shaded areas along the stream channel denote the stream section where width of riparian floodplain was quantified at 10 m intervals. a) view of the ZOBC3; SB: slope boundary across which road cut down to the saprolite layer; ZB: zero-order basin boundary, and b) a schematic diagram of the runoff monitoring system showing locations of, piezometer (P-ZOBC3), road weirs, ZOBC3 weir, and the directions of Hortonian road runoff; the shaded area on the road denotes noticeable rills where flow tended to concentrate; LB: logging road drainage boundary; A and B: gullies where road runoff drained to the downstream system. Note that the picture in panel a was taken in January 2004 immediately after catchment was clear-felled and burnt with little alteration of pre-disturbance surface topography . 108 Figure 5-2 Map of the road monitoring area (a) (the arrow indicate the view direction in the panel c); ZOBC3 weir and road runoff weir A (b); views of the experimental road section (c); a close-up view of the road weir A with a WHR probe in PVC casing (d); legends in (a) are the same that were used in Figure 5-1 109 Figure 5-3 Relations between suspended sediment concentration measured by the gravimetric method and turbidity values measured by the YSI 6000 probe. The solid line denote the regression line described in the text (see the section 5.3.3.). 114 Figure 5-4 Schematic diagram that shows the modeling approach for Hortonian overland flow estimation for the road. RA-a t(i) denotes precipitation (R) input to a sub-block (a) within the contributing area to a weir (A) at time t(i) since the onset of precipitation events. TL refers to time lag (minute) assigned to each sub-block within the contributing areas to each weir. HOFA t(i) defines the rate of Hortonian overland runoff draining through a weir (A) at the time t(i) since the onset of precipitation. Refer to the see the text to ascertain how potential road Hortonian overland flow was estimated using this hypothetical procedure. 116 Figure 5-5 Storm response of the road section on December 2002 and October 2003: a) and b) precipitation; c) and d) total flow rate and potential HOF rate at the road weirs; e) response of piezometer (P-ZOBC3); f) and g) air temperature at the road surface, runoff at weir B, and subsurface zone or flow at P-ZOBC3; h) and i) specific conductance (SP) and total solid concentration (TS) in runoff. 118 Figure 5-6 Storm response of the C3 catchment outlet on December 2002 and October 2003: a) and b) precipitation; c) and d) flow rate at the road weirs; e) and f) temperature of runoff at the weir B and at the catchment outlet; g) and h) specific conductance (SP) and IX study design did not allow such testing of the effects of topography on ISSF responses due to the absence of multiple monitored road sections crossing various landforms, total contributing area to road cuts and gradient of areas upslope of road cuts also likely affect ISSF response (e.g., Wemple & Jones, 2003). Therefore, I emphasize that road management (i.e., location and construction methods) in areas conducive to interruption of subsurface flow should carefully consider these activities in the context of dominant flow pathways and topographic characteristics of the areas. Equally important, road systems should be laid out to minimize extensive direct connectivity of source areas of sediment as well as solutes to river channel systems to reduce excessive soil transport as well as loss of nutrients from the catchments that affect site productivity and downstream water quality and aquatic habitat. As an example of an important ecological process that potentially facilitates catchment recovery after road construction and heavy use, I preliminary demonstrated that recovery of roadside fern growth (D. curranii) plays an important role in recovery of road systems. D. curranii is often recognized as a ‘nuisance plant’ because it prevents other plants from establishing beneath it due to heavy shading and formation of thickets (e.g., Wee, 1984; Russel et al., 1998). Thus, the role of this fern needs to be carefully evaluated before consideration in forest management. In the study area, natural revegetation on the surface of logging roads cannot be expected until the severely eroded and compacted surface conditions are ameliorated. Without roadside shrub growth, such a stage will not be reached until roadside trees grow large enough to provide canopy cover that reduces raindrop impact, provides organic detritus to the ground, and ameliorates microclimate for biota. D. curranii likely facilitates this process by providing cover and conditioning soils prior to the establishment of trees along the road, which may replace these functional roles. 237 This fern species is intolerant of shading and dies off in light-limited conditions under forest canopy. I observed no growth of D. curranii along a 40-year old logging road in C1 where a well-developed forest canopy exists. Instead, various types of tree species are currently growing on the road surface. Therefore, I preliminarily argue that at least within an initial period of 40 years, road surface revegetation and recovery will likely benefit from roadside fern growth. Although the upscaling effects of road recovery related to fern regrowth on the road remains unknown, management practices that does not hinder regrowth of roadside fern along with road abandonment may serve as one feasible and economical means to reduce long-lasting influences of road networks, at least in the areas that I have examined in this work. Another important implication provided by my finding in Chapter that needs to be well realized is the difficulty of natural recovers of road surface when roads are constructed deeply into the subsoil to the extent that subsurface stormflow is intercepted. 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Journal of Tropical Forest Science, 7: 199-204 252 [...]... objective of this dissertation is: To identify important intra- catchment processes related to management of forested tropical headwater catchments Three specific sub-objectives are: 1 To elucidate intra- catchment variability related to stormflow generation and solute export within a relatively undisturbed tropical headwater catchment 2 To understand how logging road networks alter processes and pathways related. .. contribution) FPSTORM – total storm-induced additional runoff, primarily in the form of overland flow, measured at the outlet of the floodplain FPSTORM-SOF – storm-induced additional runoff, primarily in the form of overland flow, measured at the outlet of the floodplain; it refers to the portion of FPSTORM that is generated due to precipitation falling onto saturated floodplain surface FPSTORM-RF – storm-induced... drawback of catchment monitoring approach is its inherent feature that integrates variability of intra- catchment processes as a part of the black-box output, providing limited information on intra- catchment processes When spatially explicit land management practices are implemented in headwater areas, 4 understanding of the heterogeneity in processes within catchment, and thus, vulnerability of various... related to stormflow generation and export of sediment and solutes within a severely disturbed tropical headwater catchment 3 To document recovery processes of roads associated with vegetation regrowth after 5 catchment disturbance related to sediment, water, and solute dynamics 1.3 Study approach Due to time constraints and limited logistical controls of research sites abroad, I did not attempt to employ... logged tropical headwater catchment Chapter 7 illustrates spatially variable source areas and contributions of sediment and solutes in the context of export from the catchment outlet within a logged tropical 7 headwater catchment Chapter 8 examines the role of roadside fern growth on road recovery within a logged tropical headwater catchment Chapter 9 summarizes the findings and management implications related. .. undisturbed catchment that presumably share similar environments such as climate, original vegetation, lithology, and soils but differ in management history In other words, temporal extensiveness of long-term field sampling was sacrificed to attain spatially extensive data within catchments, which was instrumental to elucidate poorly understood intra- catchment variability of hydrological processes and... solute dynamics in tropical ecosystems Importantly, temporal intensity of short-term field sampling was rather high to capture detailed responses of catchments during several storm events In this approach, the relatively undisturbed catchment was considered as a control that provided information on the intra- catchment processes without extensive human interventions so that a variety of processes and mechanisms,... 1.4 Outline of the dissertation To address the questions related to the three sub-objectives, the following chapters deal with specific aspects of the study: Chapter 2 provides descriptions of the study site and monitoring sites within the study site Chapter 3 examines stormflow generation processes within a relatively undisturbed zero-order basin (geomorphic hollow) of a tropical headwater catchment. .. from FStotal, whereas CSroad was equivalent to CStotal HOF – Hortonian overland flow; infiltration excess overland flow; it occurs when rainfall intensity exceeds a infiltration capacity of ground surfaces HOFpotential – a total amount of Hortonian overland flow potentially expected from the experimental road section when assuming a 100% runoff coefficient HOFROAD – event-based unit area road runoff caused... surface FPSTORM-RF – storm-induced additional runoff, primarily in the form of overland flow, measured at the outlet of the floodplain; it refers to the portion of FPSTORM that is generated due to return flow emerging at the foot of planer hillslope FStotal and CStotal – those refer to fine and coarse sediment fluxes from the experimental road section, inclusive of sediment originating from upslope (i.e., . UNDERSTANDING INTRA-CATCHMENT PROCESSES RELATED TO MANAGEMENT OF TROPICAL HEADWATER CATCHMENTS BY JUNJIRO N. NEGISHI (M.Sc.) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF. contribution) FP STORM – total storm-induced additional runoff, primarily in the form of overland flow, measured at the outlet of the floodplain FP STORM-SOF – storm-induced additional runoff, primarily. flow. Contributing areas of HOF (Hortonian overland flow) to the outlet of C3 expanded from 0.1 to over 1.5 ha with increasing storm rainfall over a range from 5 to 88 mm at least for events