Steep Upland Research Articles

Interception performance of intake structures with a flow diversion barrier under supercritical flow conditions

Intake structures are commonly used in drainage systems to redirect surface rainfall runoff into underground tunnels. The Hong Kong West Drainage Tunnel (HKWDT) system is designed to capture stormwater from steep upland catchments during periods of heavy rainfall, concurrently maintaining a minimal environmental flow downstream during dry weather. However, during heavy rainfall events, excess rainfall water is often directed into the drainage system, presenting a significant challenge to the urban drainage system. Undistorted Froude scale physical models and computational fluid dynamics (CFD) models are developed to investigate the flow performance. In this study, effects of various design parameters on water diversion performance are examined across a wide range of inflow conditions. Steeper channel bottom slopes leading to a larger proportion of water being directed downstream. Extending the length of the bottom rack effectively reduces adhering flow. Introducing a transverse barrier generates a hydraulic jump, which increases flow diversion into the LFC. With higher barrier heights, the hydraulic jump becomes stronger, facilitating greater water diversion into the downstream sewage system. The results indicate potential solutions to these challenges and provide valuable insights into optimizing flow diversion performance in intake structures, particularly in areas characterized by steep terrains and varying flow conditions.

Coastal setting determines tidal marsh sustainability with accelerating sea-level rise

There is an increasing concern over how accelerated rates of sea-level rise (SLR) will impact tidal marsh ecosystems. The present study evaluates the potential impacts of SLR on marsh sustainability using the Tidal Marsh Model (TMM) with the addition of a new vegetation algorithm within the SCHISM (Semi-implicit Cross-scale Hydroscience Integrated System Model) framework. This new functionality contributes to an improved understanding of how vegetation affects the mean flow velocity and turbulence, and consequently, the sedimentation processes. Using two SLR scenarios (intermediate and extreme SLR rates), we projected the changes in marsh extent over the next 50 years in two representative marsh systems within a subestuary of Chesapeake Bay. Each study site has marshes associated with different physical settings and anthropogenic components: Carter Creek (developed, high topography) vs. Taskinas Creek (natural, low topography, steep banks). Carter Creek experienced a net marsh loss of 7.3% and 60% in the intermediate and extreme SLR scenario, respectively. In some places, due to the local geomorphic settings, marshes were able to migrate inland and offset part of the total loss, whereas marsh transgression was truncated near development and hardened shoreline structures. In Taskinas Creek, marshes are associated with natural lands with steep upland slopes (inhibitor for marsh transgression due to SLR). Marsh net decline was 23.1% (intermediate SLR scenario), and 89.6% (extreme SLR scenario). Marsh transgression was not substantial in this site, suggesting that marsh loss can be primarily attributed to upland bank conditions which prevented marsh migration with accelerated SLR rates. The enhanced TMM provides the highly-resolved simulations of multi-scale processes needed to inform restoration, strategic planning, and monitoring activities to support marsh sustainability in an evolving system.

Fluvial Channel Branching Enforces Threshold Relief

AbstractRelief within mountain belts appears to be limited to a threshold of 1,000–1,500 m. However, it remains unclear definitively where in the landscape this threshold is found. Here we use a new method of analysis, termed Progressive Hypsometry, to show that “threshold relief” is the typical relief of first‐order fluvial catchments. The method tracks changes in the elevation frequency distribution (hypsometry) across nested catchments of all sizes. We find that self‐similar nesting of fluvial catchments leads to quasi‐scale invariance in hypsometry, such that the relief between any catchment's modal and outlet elevation (RMo, mode relief) falls into three groups: the two lower associated with steep upland subcatchments (RMo = 250–1,000 m) and the other with fluvial catchments, which span orders of magnitude in area but maintain an RMo of 1,000–1,500 m. We conclude that threshold relief is the maximum relief a first‐order fluvial catchment can develop without branching.

Saltmarsh sustainability throughout the Holocene in Boston Harbor: A new sea-level curve for the lower Gulf of Maine and implications of recent anthropogenic alteration

Saltmarsh evolution is closely linked to sea-level rise (SLR) and sediment supply. In a regime of accelerating SLR, saltmarsh survival depends on the ability of the marsh platform to grow vertically through organic and inorganic accumulation, and laterally via transgression over adjacent uplands. In formerly glaciated settings, the formation and maintenance of a saltmarsh are complicated by steep uplands, low sediment availability, isostatic rebound, changes to tidal amplitudes, and anthropogenic alteration. While much work has examined the development of large saltmarshes in New England since the mid-Holocene and Anthropocene, little is known about the smaller isolated saltmarshes that form in pockets along the glaciated coastline. We use radiocarbon dates from newly uncovered index points (basal peat) within Boston Harbor to date one of the oldest saltmarshes in the region (∼4.2 ka), and calculate the polynomial relative sea-level curve (RSLR) for the lower Gulf of Maine taking into account tidal amplification throughout the Holocene. This study informs the historical persistence of isolated saltmarshes under varying rates of sea-level rise (magnitude as much as 2 mm yr−1). Additionally, we refine the timing and rates of the mid-Holocene sea-level deceleration in this region: between 2.8 and 3.3 ka, slowing from 2.1 mm yr−1 to 0.5 mm yr−1. RSLR determined from the past century of tide gauge data is 2.86 mm yr−1, five times greater than historic rates over the past 2000 years. Recent vertical accretion rates (determined from marker horizons and 210Pb data) indicate that portions of Boston Harbor’s saltmarshes are able to keep pace with current RSLR. However, historical diking and ditching practices appear to have resulted in elevation loss and conversion from high saltmarsh platforms to low saltmarsh platforms, largely influencing the amount of inorganic sediment needed to help maintain marsh surfaces. These results highlight that knowledge of historical anthropogenic modifications and changes in hydroperiod are critical when interpreting vertical accretion results. More importantly, anthropogenic modification within sediment starved saltmarshes may be the cause for cannibalization of marsh shorelines, whereby inorganic sediment eroded from marsh edges is recycled and delivered to the surface, facilitating vertical accretion that offsets RSLR. Under modern accelerated sea-level rise and decreased sediment supply, this cannibalization process may now be the only pathway for saltmarsh survival.

Modeling long‐term salt marsh response to sea level rise in the sediment‐deficient Plum Island Estuary, MA

AbstractAn accelerating global rate of sea level rise (SLR), coupled with direct human impacts to coastal watersheds and shorelines, threatens the continued survival of salt marshes. We developed a new landscape‐scale numerical model of salt marsh evolution and applied it to marshes in the Plum Island Estuary (Massachusetts, U.S.A.), a sediment‐deficient system bounded by steep uplands. To capture complexities of vertical accretion across the marsh platform, we employed a novel approach that incorporates spatially variable suspended sediment concentrations and biomass of multiple plant species as functions of elevation and distance from sediment sources. The model predicts a stable areal extent of Plum Island marshes for a variety of SLR scenarios through 2100, where limited marsh drowning is compensated by limited marsh migration into adjacent uplands. Nevertheless, the model predicts widespread conversion of high marsh vegetation to low marsh vegetation, and accretion deficits that indicate eventual marsh drowning. Although sediment‐deficient marshes bounded by steep uplands are considered extremely vulnerable to SLR, our results highlight that marshes with high elevation capital can maintain their areal extent for decades to centuries even under conditions in which they will inevitably drown.

Assessing the response of the Great Marsh to sea-level rise: Migration, submersion or survival

To survive rising sea level, salt marshes must accrete vertically, migrate laterally, or undergo a combination of the two. If sufficient sediment is available for marsh accretion, the slope of the surrounding area is relatively flat, and edge erosion is minimal, then a marsh can theoretically maintain its areal extent through a combination of vertical accretion and upland expansion. However, in cases where sediment supply is limited and the marsh is backed by steeper slopes, it is unclear whether accretion and inland migration will be sufficient to counteract the combined effects of rising sea level and edge erosion. Given these barriers to marsh expansion, inland migration may not be a viable solution to marsh vulnerability to sea-level rise. We quantify the potential changes in areal extent under future sea-level rise scenarios for the Great Marsh in northern Massachusetts, where the marsh has a limited suspended sediment supply and relatively steep upland topography. Salt marsh is identified and classified into low or high marsh using LiDAR elevation and validated using aerial photography and vegetation surveys. We generate a simple 1D-H model using locally-measured accretion rates and their relationship to marsh elevation, to determine change in elevation and dominant plant species over time. A maximum inorganic sediment available to the marsh is prescribed for certain model scenarios to test the impact of sediment limitation. This limit is calculated based on the volumetric contribution of mineral sediment to the present marsh accretion rates. Predicted changes in marsh area over a 100-year model period are determined using the surrounding elevation gradients, calculated sediment availability, projected edge erosion, and local rates of sea-level rise (SLR). The two Representative Concentration Pathway (RCP) SLR scenarios used are based on the most recent IPCC report and also include the latest information concerning responses to ice sheet melting in Greenland and Antarctica. We find that as the rate of sea-level rise increases, the areal extent of the marsh decreases due to a lack of the suspended sediment needed to maintain marsh surface elevation and the inability of the marsh to encroach upon steep upland slopes. By comparing a model assuming constant accretion rates to one with mineral sediment-limited accretion, we find that when sediment if limited, marsh habitat conversion and loss occur earlier and more rapidly.

Incorporating sedimentological data in UK flood frequency estimation

This study presents a new analytical framework for combining historical flood data derived from sedimentological records with instrumental river flow data to increase the reliability of flood risk assessments. Historical flood records were established for two catchments through re‐analysis of sedimentological records; the Nant Cwm‐du, a small, steep upland catchment in the Cambrian Mountains of Wales, and a piedmont reach of the River Severn in mid Wales. The proposed framework is based on maximum likelihood and least‐square estimation methods in combination with a Generalised Logistic distribution; this enables the sedimentological data to be combined effectively with existing instrumental river flow data. The results from this study are compared to results obtained using existing industry standard methods based solely on instrumental data. The comparison shows that inclusion of sedimentological data can have an important impact on flood risk estimates, and that the methods are sensitive to assumptions made in the conversion of the sedimentological records into flood flow data. As current industry standard methods for flood risk analysis are known to be highly uncertain, the ability to include additional evidence of past flood events derived from sedimentological records as demonstrated in this study can have a significant impact on flood risk assessments.

Storage and export of soil carbon and mineral surface area along an erosional gradient in the Sierra Nevada, California

Steep soil-mantled hillslopes are thought to be important sources of sediments and organic carbon (OC) to rivers. Minerals in these sediments may protect OC from decomposition, yet the significance of such interactions in steep upland soils remains poorly constrained particularly in relation to erosion rates. We examined a tributary basin draining to the Middle Folk Feather River in California, where knickpoint migration has created a series of hillslopes with erosion rates varying over an order of magnitude (35 to 250 mm kyr−1). This setting provides a unique opportunity to study soil OC pools and their erosional exports as a function of changes in erosion rates. Soil OC inventories were 37% lower at rapidly eroding sites relative to slowly eroding sites. This difference was driven by coarse rock contents as rapidly eroding soils had more rock fragments, limiting their capacities to store OC. Although clay contents in soils were negatively correlated with erosion rates, the total mineral specific surface area remained relatively invariant. Based on secondary phyllosilicate minerals present in the studied soils and our field observations of saprocks, we suggest that this discrepancy may have originated from different clay mineralogy (types and abundance) associated with different degrees of deep subsurface chemical weathering. Across the erosion gradient, the radiocarbon age of mineral associated organic matter (MOC) in saprock varied by a factor 2 (from 1045 to 2110 14C years), while soil turnover times estimated from soil thickness and erosion rates varied from 17 to 5.4 kyr. At the site eroding at the fastest rate, the soil turnover time approaches the 14C age of MOC, suggesting erosion can potentially limit the timescale over which MOC is replaced. We found that organic matter generally covered <50% of the total mineral surface. The remaining OC-free mineral surface area, once eroded, may thus have a significant, and to date unquantified, capacity to adsorb additional organic matter, which may act as a long-term atmospheric carbon sink.

English

A field experiment project was conducted in Karawang District, Indonesia from April&nbsp; to October, 2016 in the search of efforts to optimize degraded steep upland paddy field and paddy yield. The experinment was designed under no tillage practices and statistical randomized block were applied with two factors, that is, banana leaf mulch, and worms where each factor is varied into four levels of treatments with three times-replication, respectively. Results showed that both banana leaf mulch and worms significantly improved the soil physic properties of degraded land such as reduced soil bulk density by 28%; increased soil water capacity by 144%; increased total porosity by 24.5% ; and soil permeability from 1.12 to 29.34 cm/h. While, the regression/corelation of this improvement to the paddy (dry-land paddy rice) tiller and yield is strong at R2 = 0.54 and R2 = 0.72, respectively. Key words: Banana leaf, mulching, degraded upland paddy field, earth-worms, paddy.

CO2 evasion from a steep, high gradient stream network: importance of seasonal and diurnal variation in aquatic pCO2 and gas transfer

Surface waters contribute substantially to carbon dioxide (CO2) emissions to the atmosphere. However, global estimates remain uncertain due to methodological difficulties, such as in precisely estimating gas transfer in steep upland streams. Here, we addressed the question of what drives CO2 evasion from steep mountainous stream network of the European Alps by assessing the spatial and temporal variation of partial pressure of CO2 (pCO2) for 148 streams and the gas transfer coefficient for CO2 (kCO2) for 88 locations within this 254 km2 watershed. Results show that log kCO2 can be predicted reasonably well (r2 = 0.71, p<0.001, n = 88) using a statistical model based on slope, average width, flow velocity and stream discharge. Also, most sites were supersaturated in CO2 with significant variation in pCO2 due to season (September vs. December) and time of day (day vs. night), but not stream order. Resulting median CO2 evasion rates were 145, 119, 46, 43, and 50 mg C m−2 h−1 at 1st to 5th order streams, respectively. CO2 evasion was dependent on season and time of day, with the highest evasion (184.0 kg C h−1) during growing season at nighttime, followed by 124.6 kg C h−1 during daytime. Dormant season nighttime evasion was 30.9 kg C h−1 and daytime evasion only 17.1 kg C h−1. Overall we conclude that CO2 evasion of steep mountainous streams depends on seasonal and diurnal variation in pCO2 and reach-specific variability in kCO2. These controls strongly alter landscape-scale CO2 evasion estimates, with implications for regional to global carbon budgets.

Characterising flash flood response to intense rainfall and impacts using historical information and gauged data in Britain

AbstractWe analyse chronologies of historical flash floods derived from searches of newspaper archives and other sources commencing before 1800 and recent gauged rainfall and stream flow data. Five key examples are chosen to illustrate specific features of flash floods. Pluvial flash floods arise from rainfall before it reaches a watercourse and may cause severe flooding of land and properties far from rivers. River flash floods, like pluvial floods, have the characteristic of rapid speed of response, a principal source of risk to life. Intense rainfall can generate ‘walls of water’ in river courses which can propagate long distances downstream and steepen, without upstream structural failure. Steeply rising wavefronts more commonly occur on steep upland catchments but, where intensities of extreme short period rainfall are sufficient, such wavefronts can also occur on lowland catchments. A definition of flash floods from intense rainfall, relevant to British landscape and climate, is proposed.

Geomorphological records of extreme floods and their relationship to decadal-scale climate change

Extreme rainfall and flood events in steep upland catchments leave geomorphological traces of their occurrence in the form of boulder berms, debris cones, and alluvial fans. Constraining the age of these features is critical to understanding (i) landscape evolution in response to past, present, and future climate changes; and (ii) the magnitude–frequency of extreme, ungauged floods in small upland catchments. This research focuses on the Cambrian Mountains of Wales, UK, where lichenometric dating of geomorphological features and palaeohydrological reconstructions is combined with climatological data and documentary flood records. Our new data from Wales highlight a distinct flood-rich period between 1900 and 1960, similar to many other UK lichen-dated records. However, this study sheds new light on the underlying climatic controls on upland flooding in small catchments. Although floods can occur in any season, their timing is best explained by the Summer North Atlantic Oscillation (SNAO) and shifts between negative (wetter than average conditions with regular cyclonic flow and flooding) and positive phases (drier than average conditions with less frequent cyclonic flow and flooding), which vary from individual summers to decadal and multidecadal periods. Recent wet summer weather, flooding, and boulder-berm deposition in the UK (2007–2012) are related to a pronounced negative phase shift of the SNAO. There is also increasing evidence that recent summer weather extremes in the mid-latitudes may be related to Arctic amplification and rapid sea ice loss. If this is the case, continuing and future climate change is likely to mean that (i) unusual weather patterns become more frequent; and (ii) upland UK catchments will experience heightened flood risk and significant geomorphological changes.

Technical Note: A Low-Cost Pressure Regulator for Improving the Water Distribution Uniformity of a Microtube-Type Drip Irrigation System

<abstract><title><italic>Abstract.</italic></title> Irrigation application using a low-cost microtube-type drip irrigation system tends to be relatively non-uniform especially under steep slopes and low operating pressure heads. This study was conducted to evaluate the effect of using a simple and inexpensive adjustable valve (AV) pressure regulator on water distribution uniformity of the low-cost microtube-type drip system under sloping conditions at various operating pressure heads. A 100 m² microtube-type drip kit developed by the International Development Enterprises (IDE) was tested for water distribution uniformity with and without AVs under average operating pressure heads of 0.5, 1.0, and 1.5 m, submain slopes of 10%, 20%, and 30%, and lateral slope of 0%. Based on volumetric measurement of emitter discharge, the average Christiansen’s coefficient of uniformity (CU) and Merriam and Keller’s distribution uniformity (DU) values improved to a range of 76% to 94% and 64% to 91%, respectively, with AV adjustment. For all pressure heads and submain slope of 30%, CU and DU were increased by an average of 25% and 82%, respectively, with AV adjustment. Pair-wise t-test comparison (α=5%) of average CU and DU values for each setting showed significant improvement of water distribution uniformity except for a combination of a high pressure head of 1.5 m and steep slopes of 20% and 30%. These exceptional results suggest that at relatively steep slopes, the microtube-type drip system may be operated at relatively low pressure heads with proper AV adjustment to increase the water distribution uniformity. Results indicated that the use of AVs can significantly improve water distribution uniformity of the low-cost microtube-type drip irrigation system at low pressure heads even at slopes as steep as 30%, and offers the potential for maximizing crop yield in steep upland areas.

Forest cover change trajectories and their impact on landslide occurrence in the tropical Andes

Tropical mountain regions are prone to landslide hazards. Given the current land pressure with increasing occupation of steep uplands, landslide hazards are expected to increase in the near future. Understanding the factors that control landslide hazards is therefore essential. Rare event logistic regression allows us to perform a robust detection of landslide controlling factors. This technique is here applied to the tropical Andes to evaluate the impact of dynamic land cover changes on landslide occurrences. Land cover change trajectories (i.e. dynamic evolution of land cover through time) were specifically included in the probabilistic landslide analysis. While natural physical processes such as slope undercutting by rivers and failure of oversteepened slopes are important in this tropical mountainous site, landslides are increasingly associated with human activities. The data show that land cover trajectories are associated with landslide patterns. In this humid mountainous site, forest degradation does not lead to a measurable increase in landslide occurrence. However, few years after forests are converted to pastures, a rapid decline of slope stability is observed. Land cover conversion from forest to pasture permanently reduces slope stability. It is assumed that major changes in soil properties and hydrology induced by the vegetation conversion play a role in accelerating landslide hazards.

Landslide erosion coupled to tectonics and river incision

The steep topography of mountain landscapes arises from interactions between tectonic rock uplift, valley incision and landslide erosion on hillslopes. An analysis of more than 15,000 landslides in the eastern Himalaya, mapped from satellite images, shows that steep uplands primarily respond to uplift and river incision by increases in landslide erosion rates rather than by steepened hillslope angles.

Impact of stone content on water movement in water‐repellent sand

SummarySoils are commonly stony, especially in steep upland or heavily degraded sites. The hydrological effect of large stone contents has been previously investigated in wettable but not in water‐repellent soils. For the latter, the focus has instead been on the impact of other soil characteristics (e.g. cracks and macropores) likely to promote water percolation. This paper investigates stone effects on water flow in water‐repellent sand under laboratory conditions. Seventy‐five experiments were performed on a water‐repellent sand mixed with a range of quantities of different‐sized wettable and water‐repellent stones. The time taken for water to pass through each sand–stone mix, the percolated water volumes and numbers of dry and wet stones following each 60‐minute experiment were recorded. At large stone contents (&gt; 55% or &gt; 65% by weight, depending on stone wettability), percolation occurred relatively quickly and in comparatively large quantities. At intermediate stone contents (45–65%) percolation response was variable and at stone contents &lt; 45% for wettable and &lt; 55% for water‐repellent soils no water percolation occurred. We argue that with large stone contents flow pathways develop along sand–stone interfaces and a continuous preferential flow path can form provided there are sufficient stone‐to‐stone connections. The distribution and alignment of the stones, especially at intermediate stone contents, are important for promoting water movement. Water repellency determinations based only on the fine sediment component in stony soils could therefore be misleading as regards determining their hydrological response: the influence of the clastic component must also be considered.

Seasonal flooding, instream habitat structure and fish assemblages in the Mulgrave River, north-east Queensland: towards a new conceptual framework for understanding fish-habitat dynamics in small tropical rivers

Strong relationships between seasonal flooding, instream habitat structure and fish assemblages have been well documented in large tropical rivers (e.g. the flood pulse concept). However, the mechanics of these relationships are likely to differ substantially in smaller coastal rivers, such as those in Costa Rica, south-east Brazil and Australia’s Wet Tropics. These systems typically feature steep upland streams with short, deeply incised lowland channels and poorly connected floodplains. This hypothesis was investigated by documenting spatial and temporal variation in fish-habitat relationships in the Mulgrave River, north-east Queensland. Sampling was conducted at four lowland sites under a range of flow conditions, from dry-season baseflows to a one-in-ten-year flood. Longitudinal environmental gradients and fine-scale habitat patches were important in regulating fish assemblage structure during the dry season. However, high wet-season flows, constrained by the deep channel, acted as disturbances rather than gentle flood-pulses. In particular, the mobilisation of bed sediments led to scouring of aquatic vegetation and a dramatic reduction in habitat heterogeneity. Seasonal movements of fish led to significant changes in assemblage structure – from a community dominated by Neosilurus ater, Hypseleotris compressa, Awaous acritosus and Redigobius bikolanus during the dry season, to one dominated by Nematalosa erebi, Ambassis agrammus and Glossamia aprion during the wet season. Based on these observations, together with information from the literature, a conceptual model of fish-habitat dynamics is presented that is better suited to small tropical rivers than those developed in larger systems with expansive floodplains.

Abiotic controls on periphyton accrual and metabolism in streams: Scaling by dimensionless numbers

Increasingly available high‐resolution topographic data from remote sensing motivates the search for topographic features that predict abiotic controls on the distribution and performance of biota. We investigated the extent to which periphyton distribution and stream ecosystem metabolism in a steep upland river drainage network could be predicted from physical conditions that varied with local topography. During the summers of 2003 and 2004, we measured periphyton standing crops and gross primary production and ecosystem respiration rates along a 5 km reach of the South Fork Eel River and six of its tributaries in northern California (39°44′N, 123°39′W). We also measured wetted stream width (B), cross‐sectionally averaged stream velocity (U), and streambed photosynthetically active solar radiation (PAR) at each site to investigate the degree to which periphyton abundance and metabolism were related to these indicators, which in turn are partially predictable from models relating environmental parameters to the topographic settings. Dimensional analysis, a technique widely used in the field of fluid mechanics, was used to investigate how biotic and abiotic variables may be interconnected in stream environments. Nondimensional groups of variables were formulated on the basis of our field estimates of chosen biotic and abiotic variables. Periphyton biomass was controlled by B9/5, exposure to light PAR1/5, nutrient concentration N5/6, and inverse stream depth H−5/6 and U−1/2. The autotrophic‐heterotrophic balance, quantified by the gross primary production to ecosystem respiration rate, scaled with the stream aspect ratio (B/H) and Peclet number Pe = (UB/u*H), where u* is the shear stress velocity. The scaling relationships were validated against reported field measurements from other geographical areas. The results show nonlinear dependencies among periphyton biomass, stream metabolism, and abiotic variables. These nonlinear relationships point to a need for detailed quantification of biotic and abiotic variables over a range of scales.

Towards Sustainable Agricultural Development of Kotawaringin Barat Regency, Kalimantan, Indonesia

ABSTRACT A study was conducted to establish an approach to land development for sustainable agriculture of the Kotawaringin Barat Regency, Kalimantan, Indonesia. The study comprised three parts, namely, developing the agroecological zone (AEZ), establishing agricultural land regions, and determining land suitability of these regions for several existing crops. On the basis of land characteristics, climatic data, 4-slope classes, and the isohyperthermic temperature regime, Kota-waringin Barat Regency was divided into four main agroecological zones. The area covered by zone I, II, III, and IV were 12.45%, 33.4%, 10.89%, and 43.26%, respectively. The steep upland areas of zone I would be left undisturbed for native forest and wildlife reservation. The moderately steep areas of zone II would be suitable for hardy perennial crops. The gentle sloping areas of zone III would be suitable for agroforestry and annual crop cultivation. Depending upon the soil types, the lowland, and swampy areas of zone IV would either be left for mangrove forest production or for annual crop cultivation. Overlaying the AEZ map with the present land use map generated an agricultural land region map, creating areas known as extensification, intensification and conservation zones. These areas are biophysically determined and ecologically sustainable. More than 60% of the total land area of Kotawaringin is suitable for agriculture, leaving almost 40% for native forest conservation. The arable agricultural lands under the extensification and intensification zones were evaluated for their suitability to some existing perennial and annual crops cultivation. The lands were classified as highly suitable (S1) to marginally suitable (S3) for commercial crops such as rubber and oil palm, and staple food crops like upland rice and wetland rice.

Ravinement en montagne : processus, mesures, modélisation, régionalisation

Cemagref (Agricultural and Environmental Engineering Research Centre) in Grenoble and the Scientific Group "Draix, mountain erosion studies" held a conference in Digne, in the French Alps, from October 15 to 17, 2003, devoted to the theme of gully erosion in mountain areas. The aims of this international seminar were to evaluate the state of the art in research on erosion by water in uplands, to allow scientists to meet and exchange ideas on related topics, and to initiate further collaborations, with particular emphasis on field work in research basins. This meeting, which encompassed 32 oral presentations and 24 posters, was attended by 80 participants from 12 countries. A one-day scientific excursion to the Draix experimental site was dedicated to multidisciplinary researches on mountain erosion and upland floods. Gully erosion represents an important sediment source in river systems and accounts for as much as 70 to 90% of the overall sediment production of a catchment. In mountain areas, the steep slopes enhance gully processes, accelerate sediment transfer from uplands to valley bottoms and generate natural hazards: mudflows, overflowing of heavily loaded floods, silting up of reservoirs, for example. Therefore, there is a need for monitoring and for experimental and modelling studies in order to forecast the effects of climatic or land use changes on sediment dynamics in mountain catchments. In mountain environments, the development of appropriate measurement and observation techniques is quite difficult. Original devices were presented, operating from the small plot scale to the large gully and catchment scales. Several presentations focused on the processes and factors controlling erosion and gullying in mountain areas: these include mechanical breakdown and chemical weathering of rocks, bed load and suspension sediment transport, in which threshold effects have a determining influence. Mass movements are also a substantial source of sediments in steep upland basins. These may occur as superficial earth flows affecting the weathered layer, and as deep-seated landslides or rock-block slides. Several papers examined the susceptibility of the terrain to the mass movements, the conditions for landslide initiation, the relations between mass movements in black marls and rockfalls in the overlying limestone levels, and the formation and propagation of debris flows. The major role of a few paroxystic events in sediment production was pointed out by several authors. Particle detachment, mass movement initiation, and sediment transport are processes subjected to threshold effects. The connectivity in the basin network may vary from one event to the other. The studies on sediment load rates during floods showed that the availability and location of sediment stocks in the channel and gully bottoms play a greater role than the transport capacity of the flow The role of the vegetation cover in diminishing sediment yields is widely accepted. Therefore, it is still necessary to understand how the aerial parts and roots of vegetation interact with runoffand erosion in order to model the evolution of gully systems subject to climatic or land use changes. These studies show that erosion modelling becomes more complex as ole goes from the plot or slope scale to the catchment scale, which necessitates a transport-distance approach.